2012

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration

Geologic Map of the Snegurochka Planitia Quadrangle (V–1), Venus

By Debra M. Hurwitz and James W. Head

Pamphlet to accompany

Scientific Investigations Map 3178
This page intentionally left blank
i

Contents

The Magellan Mission ..................................................................................................................................1

Magellan Radar Data ..........................................................................................................................1

Introduction ....................................................................................................................................................1

Magellan SAR and Related Data ................................................................................................................2

General Geology ............................................................................................................................................3

Map Units ..............................................................................................................................................4

Heavily Deformed Units .............................................................................................................4

Tessera ................................................................................................................................4

Densely Lineated Plains Material ...................................................................................5

Ridged Belt Unit .................................................................................................................5

Annulus Unit .......................................................................................................................6

Fracture Belt Unit ...............................................................................................................6

Regional Plains Units .................................................................................................................6

Dark Deformed Plains Material .......................................................................................6

Bright Deformed Plains Material ....................................................................................6

Dark Smooth Plains Material ...........................................................................................6

Bright Smooth Plains Material ........................................................................................7

Local Plains Units ........................................................................................................................7

Shield Plains Units .............................................................................................................7

Bright Deformed Corona Plains Material ......................................................................7

Dark Smooth Corona Plains Material .............................................................................8

Bright Smooth Corona Plains Material ..........................................................................8

Lobate Plains Units ............................................................................................................8

Edifice Material ..................................................................................................................8

Craters ..........................................................................................................................................9

Undifferentiated Crater Material .....................................................................................9

Structures .....................................................................................................................................9

Wrinkle Ridges ...................................................................................................................9

Simple Ridges .....................................................................................................................9

Lineament Structures ........................................................................................................9

Central Peaks ...................................................................................................................10

Steep-sided Domes .........................................................................................................10

Stratigraphic Relations of Units ......................................................................................................10

Geologic History ..........................................................................................................................................13

References Cited .........................................................................................................................................14

Tables

1. Impact craters in V–1. ............................................................................................................................18

2. Area of units mapped in V–1. ................................................................................................................20

Figures

1. Magellan synthetic aperture radar (SAR) data for Snegurochka Planitia, V-1, Venus, from lat 

75° N. to 90° N., and geologic sketch of the V–1 region with major tectonic and volcanic 

features labeled ...........................................................................................................................21

2. Magellan altimetry data with 10–30 km horizontal resolution and 80–100 m vertical resolution 

(map sheet)
ii

3. A, Venera 15/16 data fill in gaps in Magellan data; B, Geologic map based on observations 

made using Venera 15/16 data (Venus Venera 15/16 atlas, Kotelnikov and others, 1989); 

C, Geologic map based on observations made using Magellan data (map sheet)

4. A representation of identified structures within Snegurochka Planitia, V–1, including 

lineaments, wrinkle ridges, simple ridges, and small shield volcanoes (map sheet)

5. Asymmetric lobate plains associated with Sarasvati Mons and Heloha Fluctus near the 

boundary between Snegurochka Planitia and Itzpapalotl Tessera (map sheet)

6. Impact craters found in Snegurochka Planitia, V–1 (map sheet)

7. Regional plains near Klenova crater that have been extensively deformed by wrinkle ridges 22

8. Spatial distributions of unit classes identified within V–1 (map sheet)

9. Examples of the heavily deformed units described in the text .......................................................23

10. Topographic profiles of three ridged belts observed in V–1, with the extent of each belt 

represented in bold on each profile .........................................................................................24

11. Topographic profiles of three fracture belts observed in V–1, with the extent of each belt 

represented in bold on each profile .........................................................................................25

12. Examples of regional plains units described in the text .................................................................26

13. Examples of localized plains units described in the text ...............................................................27

14. Examples of the stratigraphy of small shield volcanoes observed in V–1 (map sheet)

15. Examples of structures described in the text ..................................................................................28

16. Stratigraphic relations of tessera (map sheet)

17. Stratigraphic relations of densely lineated plains unit pdl (map sheet)

18. Stratigraphic relations of fractures associated with Anahit Corona (left of image) and 

Pomona Corona (lower right of image) (map sheet)

19. Stratigraphic relations of the ridged belt unit rb (map sheet)

20. Stratigraphic relations of regional plains units pdd, pbd, pds, and pbs (map sheet)

21. Stratigraphic relations of individual shield volcanoes and shield plains units psh1 and psh2

(map sheet)

22. Stratigraphic relations of fracture belts (unit fb) (map sheet)

23. Stratigraphic relations of lobate plains (unit pla) (map sheet)
1

The Magellan Mission

The Magellan spacecraft orbited Venus from August 10, 

1990, until it plunged into the Venusian atmosphere on October 

12, 1994. Magellan Mission objectives included (1) improving 

the knowledge of the geological processes, surface properties, 

and geologic history of Venus by analysis of surface radar characteristics, topography, and morphology and (2) improving the 

knowledge of the geophysics of Venus by analysis of Venusian 

gravity.

The Magellan spacecraft carried a 12.6-cm radar system to 

map the surface of Venus. The transmitter and receiver systems 

were used to collect three data sets: (1) synthetic aperture radar 

(SAR) images of the surface, (2) passive microwave thermal 

emission observations, and (3) measurements of the backscattered power at small angles of incidence, which were processed 

to yield altimetric data. Radar imaging and altimetric and radiometric mapping of the Venusian surface were accomplished in 

mission cycles 1, 2, and 3 from September 1990 until September 1992. Ninety-eight percent of the surface was mapped with 

radar resolution on the order of 120 m. The SAR observations 

were projected to a 75-m nominal horizontal resolution, and 

these full-resolution data compose the image base used in 

geologic mapping. The primary polarization mode was horizontal-transmit, horizontal-receive (HH), but additional data for 

selected areas were collected for the vertical polarization sense. 

Incidence angles varied between about 20° and 45°.

High-resolution Doppler tracking of the spacecraft took 

place from September 1992 through October 1994 (mission 

cycles 4, 5, 6). Approximately 950 orbits of high-resolution 

gravity observations were obtained between September 1992 

and May 1993 while Magellan was in an elliptical orbit with a 

periapsis near 175 km and an apoapsis near 8,000 km. An additional 1,500 orbits were obtained following orbit-circularization 

in mid-1993. These data exist as a 75° by 75° harmonic field.

Magellan Radar Data

Radar backscatter power is determined by (1) the morphology of the surface at a broad range of scales and (2) the intrinsic 

reflectivity, or dielectric constant, of the material. Topography at 

scales of several meters and larger can produce quasi-specular 

echoes, and the strength of the return is greatest when the local 

surface is perpendicular to the incident beam. This type of 

scattering is most important at very small angles of incidence, 

because natural surfaces generally have few large tilted facets 

at high angles. The exception is in areas of steep slopes, such as 

ridges or rift zones, where favorably tilted terrain can produce 

very bright signatures in the radar image. For most other areas, 

diffuse echoes from roughness at scales comparable to the radar 

wavelength are responsible for variations in the SAR return. In 

either case, the echo strength is also modulated by the reflectivity of the surface material. The density of the upper few wavelengths of the surface can have a significant effect. Low-density 

layers, such as crater ejecta or volcanic ash, can absorb the incident energy and produce a lower observed echo. On Venus, a 

rapid increase in reflectivity exists at a certain critical elevation 

above which high-dielectric minerals or coatings are thought to 

be present. This leads to very bright SAR echoes from virtually 

all areas above that critical elevation.

The measurements of passive thermal emission from 

Venus, though of much lower spatial resolution than the SAR 

data, are more sensitive to changes in the dielectric constant 

of the surface than to roughness. They can be used to augment 

studies of the surface and to discriminate between roughness 

and reflectivity effects. Observations of the near-nadir backscatter power, collected using a separate smaller antenna on 

the spacecraft, were modeled using the Hagfors expression 

for echoes from gently undulating surfaces to yield estimates 

of planetary radius, Fresnel reflectivity, and root-mean-square 

(rms) slope. The topographic data produced by this technique 

have horizontal footprint sizes of about 10 km near periapsis 

and a vertical resolution on the order of 100 m. The Fresnel 

reflectivity data provide a comparison to the emissivity maps, 

and the rms slope parameter is an indicator of the surface tilts, 

which contribute to the quasi-specular scattering component.

Introduction

The Snegurochka Planitia region (V–1 quadrant, fig. 1A) 

is a predominantly low-lying terrain that covers the north polar 

region of Venus, extending from lat 75° N. to 90° N. and from 

long 0° E. to 360° E. The plains associated with Snegurochka 

Planitia (fig. 1B) abut the highlands of Metis Mons to the south 

from approximately long 240° E. to 300° E. (V–6) and the highlands of Ishtar Terra to the south from approximately long 300° 

E. to 60° E. (Lakshmi Planum, V–7; Fortuna Tessera, V–2). 

The plains of Louhi Planitia also lie within the V–1 region and 

form the northern border with the highlands of Tethus Regio 

from approximately long 60° E. to 120° E. (V–3 Meskhent 

Tessera, Ivanov and Head, 2008) and with the lowlands of 

both Atalanta Planitia (V–4, Ivanov and Head, 2004b) and 

the nearby deformed region containing a series of ridged belts 

(V–5, Pandrosos Dorsa, Rosenberg and McGill, 2001) from 

approximately long 120° E. to 240° E. The plains generally 

lie between +500 m and -500 m of the mean planetary radius 

(MPR) of 6051.8 km (fig. 2, on map), with the highest terrain in 

the region, the northernmost extent of Ishtar Terra (Itzpapalotl 

Tessera, lat 75° N., long ~315° E.), rising more than 6.4 km 

above MPR.

Prior to the collection of Magellan radar data, the Soviet 

Venera 15 and 16 missions offered the only data of the north 

polar region of Venus (Basilevsky and others, 1986; Barsukov 

and others, 1986), a region that was not imaged by Earth-based 

radar studies (Campbell and Burns, 1980; Jurgens and others, 

1980; Arvidson and others, 1990; Jurgens and others, 1990; 

Plaut and Arvidson, 1992) or Pioneer-Venus imagery (Masursky and others, 1980; Pettengill and others, 1980). The data 

collected during the Venera missions (fig. 3, on map) indicated 

that the plains of the north polar region were often deformed 

by sub-parallel linear ridges organized either in ridged belts or 

in clusters within regional plains, by clusters of small domelike hills, and by impact craters (Barsukov and others, 1985). 
2

The most prominent ridged belt identified (Dennitsa Dorsa) 

was described as extending from Atalanta Planitia to the north 

pole (lat ~l60° N. to 90° N.) along the long 200° E. meridian 

before turning south along the long 80° E. meridian to abut the 

eastern edge of the Ishtar Terra highlands as Szél-anya Lineae. 

The dome-like hills identified ranged in diameter from 1–15 

km and were interpreted to be widely distributed or clustered 

volcanic domes or cones. Impact craters were observed to have 

a range in morphologies, including simple bowl-shaped craters, 

the more common flat-bottomed crater with central peaks and 

prominent rims, and one multi-ringed crater, Klenova (lat 78.2° 

N., long 104.7° E.). Klenova crater, with a diameter of 140 km, 

represents one of the largest impact craters identified on Venus 

(Barsukov and others, 1985). Analyses of data collected during 

the Venera 15 and 16 missions (Kotelnikov and others, 1989; 

fig. 3B, on map) indicated a surface that was subjected to vast 

volcanism and a tectonic style unique from terrestrial-style plate 

tectonics but with exhibitions of horizontal tectonic deformation 

not seen on the Moon, Mercury, or Mars (Basilevsky and others, 

1986).

The Magellan mission returned higher resolution radar and 

altimetry data that has facilitated a more detailed analysis of the 

geologic history of Venus (for example, Ford and others, 1989; 

Arvidson and others, 1991; Phillips and others, 1991; Baker 

and others, 1992; Campbell and others, 1992; Head and others, 

1992; Saunders and others, 1992; Schultz, 1992; Solomon and 

others, 1992; Tyler and others, 1992; Bindschadler, 1995; Greeley and others, 1995). The north polar region of Venus offers a 

unique opportunity to observe (1) tectonic interactions between 

the highest topography in the region, Itzpapalotl Tessera, and 

the low-lying plains of Snegurochka and Louhi Planitiae to 

the north, as well as, (2) major volcanic processes that provide 

insight into the geologic evolution of the planet. Analysis of 

tectonic interactions between Itzpapalotl Tessera and Snegurochka Planitia conducted from the perspective of Lakshmi 

Planum (V–7) suggests that the high terrain of Lakshmi Planum 

formed due to large-scale contraction and underthrusting of 

plains units from the north beneath the ancient crustal block of 

Lakshmi Planum to the south (Ivanov and Head, 2009). Further 

analysis of Snegurochka Planitia (V–1) can further constrain 

this interpretation.

The spatial and temporal relations between contractional 

and extensional features such as ridged belts and fracture belts 

can refine constraints on theories of the timing and nature of the 

decline of tectonic activity interpreted from the surface geology suggested previously (for example, Herrick, 1994; Kaula 

and others, 1994; Kaula, 1995; Simons and others, 1997; Head 

and Basilevsky, 1998; Basilevsky and Head, 1998; Nimmo 

and McKenzie, 1998; Phillips and Hansen, 1998; Basilevsky 

and Head, 2000). Similarly, relations between various forms 

of volcanism observed in this region, including distributed and 

clustered small shield volcanoes, regional volcanic plains, and 

isolated large shield and steep-sided volcanoes, can provide 

insight into the evolution of the crust and mantle of Venus. 

These issues provide a framework for analysis of our geologic 

map of Snegurochka Planitia (V–1).

Traditional methods of geologic unit definition and characterization for the planets (for example, Wilhelms, 1990) are 

modified for the radar dataset available for Venus (for example, 

Tanaka, 1994; Ivanov and Head, 2001; Basilevsky and Head, 

2000; Ivanov and Head, 2009). Geologic units and boundary 

relations are mapped using mosaics of full-resolution Magellan 

synthetic aperture radar (SAR) F-MIDR, F-Map, and C1-MIDR 

data loaded into ArcGIS mapping software at a scale of 1:5 million. Digital versions of Magellan altimetry data are also used to 

analyze the geology within Snegurochka Planitia (V–1). Venera 

15/16 data was not used to supplement the current mapping 

effort for two reasons: (1) the difference between the resolutions of the two data sets is significant and thus makes mapping 

on a consistent scale throughout the region impossible, and 

(2) the region has already been mapped at a larger scale using 

the Venera 15/16 data (Kotelnikov and others, 1989; fig. 3, on 

map), and these results yield similar interpretations of regional 

geologic units and stratigraphy. Several differences can be identified between the two interpretations, however. For example, 

Szél-anya Lineae was identified as a distinct geologic unit (specifically, a fracture belt, unit fb) from the ridged belt (unit rb) of 

Dennitsa Dorsa using Magellan data whereas it was identified 

as the same geologic unit (specifically, a ridged belt, unit rb) 

using Venera data. Also, additional lobate plains units (units pla

and plb) and regional plains subunits (units pbs, pds, pbd, and 

pdd) were identified using Magellan data. These differences 

in identification can be attributed to the significant increase in 

resolution of Magellan data relative to Venera data.

Magellan SAR and Related Data

Mapping was completed using data collected by the synthetic aperture radar (SAR) aboard the Magellan spacecraft. The 

Magellan SAR instrument operated at a wavelength of 12.6 cm 

(S-band) with horizontal and parallel transmit/receive polarization that allowed for cloud penetration and for discrimination of 

wavelength-scale surface roughness. The data has an effective 

slant-range resolution of 88 m and an along-track resolution of 

120 m for each orbital swath of 20 km x 17,000 km. The majority of the SAR images of the north-polar region (lat 75° N.–90° 

N.) were collected during Cycle 1 of the mission (September 15, 

1990–September 15, 1991) at incidence angles i of 16.5°–22.0°, 

with some overlap occurring at lat 75° N. in Cycle 2 (through 

September 15, 1992, i = 24.4°), Cycle 3 (through September 14, 

1992, i = 27.1°), and Cycle 3 stereo (i = 13.4°, Ford and others, 

1993).

The images returned by the Magellan SAR instrument have 

a maximum resolution of 75 m/pixel and reveal variations in 

surface brightness that reflect surface characteristics including 

roughness, composition, and slope. Relatively bright surfaces 

indicate a rougher surface texture whereas relatively dark 

surfaces represent smoother surface texture at available radar 

wavelengths, and features oriented perpendicular to the illumination direction appear more prominent than features oriented parallel to the illumination direction. More specific guidelines for 

geologic mapping using this data and interpreting the data can be 

found in Saunders and others (1992), Ford and Pettengill (1992), 

Tyler and others (1992), Ford and others (1993), and Tanaka 
3

(1994). In addition to radar data, altimetry data, with a footprint 

of 27 km (E-W) by 15 km (N-S) and a vertical resolution of 

80–100 m in the vicinity of lat 80° N., was used in conjunction 

with stereo data (left- and right-look C1-MIDR images combined into a single three-dimensional image) to establish spatial 

and stratigraphic relations between units (Ford and others, 1993). 

Data sets associated with emissivity (passive thermal radiation), 

reflectivity (surface electrical properties), and rms slope (distribution of radar wavelength scale slopes) were also used to a 

lesser extent to aid in interpretations of unit boundaries.

General Geology

The geologic record of Snegurochka Planitia (V–1) 

includes features formed from three fundamental geologic processes: tectonism, volcanism, and impact cratering. The tectonic 

features generally appear bright in the radar backscatter data and 

can be confined in belts or distributed in asymmetrical patches 

within surrounding plains. Topography and morphology of these 

features vary across the region, indicating that several modes of 

tectonic activity influenced the geology we currently observe on 

the surface. The features with the highest elevation observed in 

the region are the northernmost extent of Ishtar Terra, Itzpapalotl 

Tessera (lat ~75° N., long 300° E.–330° E.), and the northernmost extent of Fortuna Tessera (lat ~75° N., long ~10° E.–30° 

E.). Other identified units of tessera lie near lat 87° N., long 11° 

E. and lat 81.6° N., long 87.9° E. These mountain-like regions 

range in elevation from 1.6 to 6.4 km above mean planetary 

radius (MPR = 6051.8 km, fig. 2, on map) and represent some of 

the most heavily deformed terrains on the planet.

Other tectonically deformed terrains are concentrated into 

belts 35–200 km wide and thousands of kilometers long and 

consist of either contractional or extensional features that are 

characterized by ranges in elevation from 1.5 km below MPR 

to 1.5 km above MPR. The most prominent deformation belt, 

Dennitsa Dorsa, is a positive-relief feature in the low-lying 

plains region that crosses the region at long ~200° E., extending 

to lat 90° N. before turning and continuing as Szél-anya Lineae 

south along long ~80° E. (see fig. 1). Dennitsa Dorsa is characterized by clusters of parallel-striking ridges suggestive of a 

contractional origin (Frank and Head, 1990), whereas Szél-anya 

Lineae is characterized by clusters of parallel-striking fissures 

suggestive of an extensional origin. Other ridged belts with 

similar morphology to Dennitsa Dorsa include Lukelong Dorsa, 

a negative-relief feature in the intermediately elevated plains 

near lat 76° N., long 170° E., and Fulgora Dorsa, a moderately 

positive-relief feature near the topographic boundary between 

the high terrains of Iztpapalotl Tessera and the low plains of 

Snegurochka Planitia near lat 78° N., long 340° E. Other fracture belts with similar morphology to Szél-anya Lineae include 

Tezan Lineae (lat ~84.8° N., long 17.5° E.), a negative-relief 

feature in low-lying plains, and a positive-relief fracture belt 

associated with Laka Mons, a large shield volcano near lat 80° 

N., long 265° E.

Other regions of contractional and extensional deformation 

not confined to belts are scattered throughout the region and are 

characterized by generally jagged wrinkle ridges and relatively 

straight grabens, respectively (fig. 4, on map). The plains unit 

located between latitudes <75° N. and 82° N. and longitudes 

82° E. and 172° E., for example, contains a high concentration 

of wrinkle ridges, suggesting these plains underwent significant 

contraction after emplacement. More recent extensional activity is also indicated in concentrations of grabens cutting plains 

between latitudes 75° N. and 77° N. and longitudes 180° E. and 

190° E., for example, as well as near the Anahit and Pomona 

Coronae features (see fig. 1) between latitudes 75° N. and 81° 

N. and longitudes 270° E. and 330° E.

Volcanism represents the second fundamental process 

observed in the geologic record of V–1. Volcanism is expressed 

in the region through three main classes of features, including regional volcanic plains, large volcanic features (including 

shield volcanoes and coronae), and small edifices (including 

steep edifices, steep-sided domes, and small shield volcanoes). 

Regional plains materials generally are located at low elevations 

(within 500 m of MPR) and vary in radar brightness with darker 

units forming smoother terrain. Similar units investigated elsewhere on Venus are interpreted to be vast fields of potassiumrich mafic lava flows (for example, Surkov and others, 1986; 

Kargel and others, 1993) that formed either during one catastrophic episode of volcanic activity (Herrick, 1994; Strom and 

others, 1994; Basilevsky and Head, 1995), during many brief 

but major episodes of volcanic activity (for example, Phillips 

and others, 1992), or due to a combination of catastrophic and 

episodic tectonic events (for example, Solomon, 1993) between 

0.3–1.0 Ga (Schaber and others, 1992; Phillips and others, 

1992; Solomon, 1993; Herrick, 1994; Strom and others, 1994). 

The two major plains regions in V–1 include Snegurochka 

Planitia and Louhi Planitia, and the plains are separated by the 

major deformation belts Dennitsa Dorsa and Szél-anya Lineae 

that extend through the region.

The large volcanic features of the region are generally 

located within the regional plains units and include large shield 

volcanoes (>100 kilometers in diameter) and coronae. The large 

shield volcanoes are characterized by significant central topographic highs that rise 0.5–2.0 km above the surrounding plains 

and act as sources of lava flows that can extend for more than 

250 km across surrounding units (that is, Renpet Mons, lat 77° 

N., long 235° E.). Laka Mons, a slightly smaller shield volcano 

located at lat 80° N., long ~265° E. with lava flows extending less than 140 km across surrounding units, appears to be 

associated with fractured material that may have influenced the 

emplacement of the volcano. Sarasvati Mons located at lat 75.5° 

N., long ~353° E. has lava flows that extend more than 170 km 

across surrounding units and formed near the boundary between 

the elevated Ishtar Terra terrain and the low-lying Snegurochka 

Planitia regional plains. The associated asymmetric flows appear 

to be influenced by local slopes (see fig. 5, on map). These large 

volcanoes are generally isolated from major tectonic features and 

appear to be randomly distributed within Snegurochka Planitia.

Similar to the large volcanic features, coronae are characterized by early uplift and volcanism and are thus interpreted to 

form over sites of mantle upwelling (for example, Pronin and 

Stofan, 1990; Stofan and Head, 1990; Stofan and others, 1992). 

However, in contrast to large shield volcanoes, coronae are 
4

subsequently modified by gravitational relaxation, leading to the 

formation of a raised, tectonically deformed plateau with a sagging central low surrounded by a trough (for example, Pronin 

and Stofan, 1990; Janes and others, 1992; Squyres and others, 

1992b; Roberts and Head, 1993; Smrekar and Stofan, 1997). 

Observations of crater frequencies and stratigraphic relations 

of radial tensile grabens with surrounding units suggest that 

coronae may have been active within the last 500 Ma (Namiki 

and Solomon, 1994), though areas used in these analyses might 

be too small to be statistically significant (Guest and Stofan, 

1999). Snegurochka Planitia (V–1) includes three full coronae 

and one partial corona (Bachue Corona in V–6, Metis Mons; lat 

75° N., long 261° E.), with Anahit Corona (lat 77° N., long 280° 

E., 400 km diameter) and Pomona Corona (lat 79° N., long 300° 

E., 350 km diameter) located completely within the plains of 

Snegurochka Planitia and Maslenitsa Corona (lat 77° N., long 

205° E., 200 km diameter) located on Dennitsa Dorsa, between 

Snegurochka Planitia and Louhi Planitia. When considered with 

the large shield volcanoes, there is a noticeable concentration of 

large-scale volcanic activity within Snegurochka Planitia relative to Louhi Planitia.

Other features associated with volcanic activity observed 

within V–1 are lava channels. There are two channels observed 

within dark smooth regional plains material, one located in 

Snegurochka Planitia (188.3 km long; lat 82° N., long 266° E.) 

and one in Itzpapalotl Tessera (216.8 km long; lat 76.5° N., long 

338° E.), and several channels associated with lobate plains 

materials on the northern flanks of Renpet Mons (75 km, 25.2 

km, 30.5 km, and 39.1 km long; lat 76° N., long 236° E.). The 

channels in the dark smooth regional plains units appear to be 

sinuous and to cut through the plains units as well as through and 

around structures that deform the plains units. These observations indicate that the channels formed after the majority of the 

plains were emplaced rather than at the same time. In contrast, 

the four smaller channels observed on the flanks of Renpet Mons 

appear to have transported material downslope, and some have 

deposits along the margins of the channel. The morphology and 

location of these channels indicates that the channels formed at 

the same time as the lobate flows associated with the volcano.

Twenty-three impact craters were identified in the quadrangle (table 1, fig. 6, on map), ranging in diameter from 2.9 

km (unnamed crater: lat 80.9° N., long 226.4° E.) to 143.5 km 

(Klenova crater: lat 78.2° N., long 104.7° E.). The majority of 

the craters (19) mapped are characterized by a flat floor, and 14 

have central peaks. Three of the remaining craters have been 

deformed by subsequent tectonic activity, and one crater, Klenova, is a large multi-ring basin surrounded by secondary craters. All but six of the craters identified are filled with radar dark 

material, with the remaining six craters filled with radar bright 

material; the infilled material may represent volcanic deposits 

or impact melt and breccia deposits. Some of the smaller craters 

(Eugenia: 6 km; Tunde: 15.0 km; unnamed cluster: 5.7 km, 7.5 

km, 5.0 km) appear to be part of small clusters of impacts, suggesting that the dense atmosphere of Venus breaks smaller projectiles apart prior to impact (for example, Phillips and others, 

1991; Schultz, 1992). A similar phenomenon might explain 

the formation of a diffuse ring of material surrounding a small 

central peak southeast of Klenova crater (lat 77.4° N., long 

109° E.), where the diffuse material might represent windblown 

material radiating away from a shock wave that originated from 

an impacting bolide that exploded above the surface.

Snegurochka Planitia (V–1) does not show significant 

evidence for aeolian activity in wind streaks or deposits piled 

against topographic highs, suggesting either that surface deposits are resistant to erosion or that surface winds are not significant in this region. One possible exception to this might lie in 

radar dark plains heavily deformed by wrinkle ridges between 

latitudes <75° N. and 82° N. and between longitudes 82° E. and 

172° E. (see fig. 7A). Many of the ridges in this area have radar 

bright deposits, generally along one side of the ridge, that may 

be consistent with redistributed ejecta material or reworked 

mass-wasted debris (for example, Greeley and others, 1995). 

However, the radar bright deposits do not consistently lie on the 

same side of all the ridges, a trend that would be expected in the 

presence of a prevailing wind direction, and some deposits lie 

on both sides of the same ridge. While a prevailing wind direction is not required, the disorganized distribution of the radar 

bright material in this area suggests that aeolian reworking is an 

unlikely phenomenon, though aeolian reworking may still occur 

in isolated areas (see fig. 7B). A possible alternative theory to 

the formation of these bright deposits is that older radar bright 

plains were first deformed by wrinkle ridges, generating uneven 

topography consistent with ridged terrain, and then these radar 

bright plains were subsequently embayed by younger radar dark 

lava flows (Ivanov, M., 2008, oral commun.).

Map Units

The surface of Snegurochka Planitia (V–1) exhibits 

complex interactions between different materials and structural 

units. Geologic mapping facilitates the generation and interpretation of a sequence of geologic activity that can provide 

insight into the history of this region of Venus. Units are generally mapped based on variations in surface roughness or radar 

brightness; these variations are interpreted to indicate the presence or lack of resolvable deformation that can be associated 

with observed geologic regions and features. Unit boundaries 

are distinguished where surface textures observed in the primary 

surface material change across a visible boundary. There are 

several areas dominated by structural deformation that masks 

underlying material properties, and thus these areas are defined 

according to convention as distinct units because identification of the primary material is no longer possible (for example, 

Tanaka, 1994; Ivanov and Head, 2009). Spatial distributions of 

heavily deformed units, regional plains units, and local plains 

units are shown in figure 8, and descriptions of regional plains 

units, local plains units, and structures follow descriptions of the 

heavily deformed units identified within V–1.

Heavily Deformed Units

Tessera

Tessera (units ta, tb, fig. 9A) are radar bright materials that 

are generally elevated and are characterized by significant deformation of precursor terrain and high densities of deformation 
5

structures (for example, Barsukov and others, 1985; Basilevsky 

and others, 1986; Bindschadler and Head, 1991; Sukhanov, 

1992; Solomon and others, 1992; Hansen and Willis, 1998; 

Hansen and others, 2000; Ivanov and Head, 1996, 2009). Unit ta

exhibits a high density of two intersecting orientations of deformation and occupies 290 x 103 km2 or 4.4% of the total area of 

V–1 (table 2), and unit tb, which occupies 17 x 103 km2 or 0.2% 

of the total area, appears to be an elevated and deformed terrain 

with evidence of significant folding. Although unit tb has a more 

subdued characteristic deformation pattern, it still displays evidence of extensive deformation in its radar bright, heavily folded 

texture, leading to its classification as a subunit of tessera.

The tessera material unit ta associated with the northern 

boundary of Itzpapalotl Tessera (lat ~75° N., long 300° E.–330° 

E.) generally has an elevation of ~3 km above MPR and represents the highest topography in the V–1 region. The other major 

outcrops of tessera, located near lat 87° N., long 1° E. and near 

lat 81.6° N., long 87.9° E., lie in regions that lack topography 

data, but they appear similar in morphology to the other locations, suggesting that tessera also lie at higher elevations than 

the surrounding terrain though at significantly lower elevations 

than Itzpapalotl Tessera. In all cases observed in this region, tessera units are embayed or modified by adjacent material units, 

as is evident in the discontinuation of deformation lineaments 

at these boundaries. Multiple theories have been proposed for 

the origin of tessera terrain (Bindschadler and Head, 1991, and 

references therein), including deformation driven by asthenospheric flow (Basilevsky, 1986), gravity sliding above either 

asthenospheric upwellings (Sukhanov, 1986; Smrekar and Phillips, 1988) or mantle upwellings (Pronin, 1986), gravity sliding 

driven by topographic gradients (Kozak and Schaber, 1986), 

and convergence of large lithospheric plates or downwelling 

mantle flow (Bindschadler and Parmentier, 1990). However, 

the deformation and topography associated with the tessera terrains juxtaposed to Snegurochka Planitia, western Ishtar Terra 

and Lakshmi Planum, have been interpreted as most consistent 

with mantle downwelling (Bindschadler and Parmentier, 1990; 

Bindschadler and others, 1990; Bindschadler and Head, 1991). 

Specifically, within V–1, observed trends of raised topography 

and of terrain consistently embayed or deformed by surrounding 

units are consistent with the idea that tessera formed initially 

due to substantial contraction and subsequent uplift and crustal 

thickening early in the geologic history of the region (Phase I, 

Ivanov and Head, 1996), followed by the formation of secondary deformational lineaments within exposed units, consistent 

with a later episode of tension (Phase II).

Densely Lineated Plains Material

Densely lineated plains material (unit pdl, fig. 9B) is radar 

bright material that is characterized by significant deformation 

in generally one orientation (for example, McGill, 2000; Rosenberg and McGill, 2001; Campbell and Campbell, 2002; Stofan 

and Guest, 2003; Basilevsky, 2008; Ivanov and Head, 2009). 

This deformation is expressed in parallel ridges and grooves 

that are typically spaced less than 1 km apart. The mapped unit 

pdl outcrops in V–1 are generally concentrated in Snegurochka 

Planitia (fig. 1) with few outcrops in Louhi Planitia, and the 

unit covers 950 x 103 km2, or 14% of the region. Most deposits 

of unit pdl are small (<100–200 km across), though the largest 

deposits mapped have dimensions of ~100 km by ~400 km and 

are located between latitudes 80° N. and 82° N. and between 

longitudes 230° E. and 250° E. These larger unit pdl deposits 

lie ~200 m above MPR. Like tessera, the densely lineated plains 

materials are consistently embayed by surrounding plains units, 

indicating that they formed during an early stage of intense 

tectonic deformation.

Ridged Belt Unit

Ridged belt materials (unit rb, fig. 9C) form radar bright 

deposits and is characterized by belts of single-orientation 

deformation ridges. Similar features have been identified in 

other regions of Venus, and ridged belt properties and theories 

of origin are discussed at length in the literature (for example, 

Kryuchkov, 1990; Frank and Head, 1990; Squyres and others, 

1992b; Rosenberg and McGill, 2001; Bridges and McGill, 

2002). Ridged belts range in width from ~10 km to >200 km 

and span tens of kilometers to ~2000 km in length, covering 

440 x 103 km2 or 6.6% of the V–1 region. The largest ridged 

belt in the region, Dennitsa Dorsa, ~200 km wide by ~2000 

km long, forms a topographic boundary that separates the two 

major regional plains units, Snegurochka Planitia and Louhi 

Planitia (fig. 1). The topographic signature of Dennitsa Dorsa 

is complex (fig. 10A), with a trough on each side that dips 

~600 m below MPR and the neighboring plains and a ridge in 

the center that rises nearly 700 m above MPR. This trend is 

not always observed in ridged belts, however (fig. 10B,C); the 

smaller ridged belts in the region exhibit a negative topography 

of ~800 m below the surrounding plains (~200 m below MPR, 

Lukelong Dorsa, lat 76° N., long 170° E.) or a positive topography of ~600 m above the surrounding plains (~1.4 km above 

MPR, Fulgora Dorsa, lat 78° N., long 340° E.). The observation 

of ridged belts with positive topography and ridged belts with 

depressed topography may indicate that these features represent 

a continuum of deformation, from broad arches (Fulgora Dorsa) 

representing small amounts of shortening, through asymmetric 

ridge belts (Dennitsa Dorsa) to ridge belts with troughs (Lukelong Dorsa) that may represent underthrusting (Frank and Head, 

1990).

Ridged belts appear to have a more complex stratigraphy 

than the previous two heavily deformed units. Dennitsa Dorsa 

appears to be consistently embayed by surrounding regional 

plains at all shared boundaries, as plains units cover deformation structures associated with the ridged belt. Smaller ridges 

possibly associated with flexure along the margins of the ridged 

belt may prevent these embaying plains from flooding the lowlying areas of Dennitsa Dorsa. This observation of embayment 

suggests that Dennitsa Dorsa likely formed early in the geologic 

history of this region, possibly at a time similar to the formation 

time of tessera and the majority of the densely lineated plains 

deposits. Similarly, the boundaries of the main belt of Lukelong 

Dorsa also appear to be embayed by regional plains units (fig. 

10B). However, the high concentration of wrinkle ridges that 

runs roughly parallel to Lukelong Dorsa in the surrounding 

regional plains indicates a continued compressive stress regime 
6

in this area, possibly indicating that the formation of Lukelong 

Dorsa has been reactivated more recently in the geologic history 

of this region.

Annulus Unit

Annulus materials (unit an, fig. 9D) are also radar 

bright features that are characterized by significant deformation in generally one orientation, but unlike unit pdl, unit an

is characterized by broadly concentric deformation patterns. 

Four outcrops of unit an are observed in V–1, associated with 

Maslenitsa Corona (lat 76° N., long 201° E.), Bachue Corona 

(in V–6, Metis Mons; lat 75° N., long 261° E.), Anahit Corona 

(lat 77° N., long 277° E.), and Pomona Corona (lat 79° N., long 

296° E.), occupying 100 x 103 km2, or 1.5% of the region. Unit 

an typically lies approximately 0.8 km–1.5 km above MPR 

and is associated with deformation caused by the formation of 

coronae. Some instances of tessera also appear to be associated 

with coronae annuli, particularly with Maslenitsa Corona and 

Pomona Corona, indicating that the deformation that occurs 

during corona formation can produce heavily folded terrain 

(subunit ta) as well as concentrically deformed terrain (unit an). 

The annuli of the coronae are typically embayed by surrounding regional plains materials, indicating that these features also 

formed during an early period in the geologic history of V–1.

Fracture Belt Unit

Fracture belt materials (unit fb, fig. 9E) consist of tectonic 

features characterized by radar bright terrain and typically parallel fractures confined to a belt of deformed material. Similar 

features have been identified and discussed previously in the 

literature as linear ridge terrain (Solomon and others, 1992), as 

fracture belts (Squyres and others, 1992a; Basilevsky and Head, 

2000), and, for some locales identified within V–1, as rift zones 

(Stofan and others, 1989). In V–1, these belts occupy 200 x 103

km2 or 3.1% of the total area and range from tens of kilometers to ~100 km in width and from ~200 km to more than 1200 

km in length, with the largest fracture belt, Szél-anya Lineae, 

extending ~1200 km south along a longitude of 80o with an 

average width of ~70 km. The topographic signature of fracture 

belts varies across the region (fig. 11); portions of Tezan Lineae 

(fig. 11A, lat 84.8° N., long 17.5° E.) are ~1 km below the surrounding plains (~1.6 km below MPR), portions of Szél-anya 

Lineae (fig. 11B) are ~700 m below neighboring plains (~1.2 

km below MPR), and portions of the fracture belt associated 

with Laka Mons (fig. 11C, lat 80° N., long 259.4° E.) are ~200 

m above the surrounding plains (~400 m above MPR). These 

topographic characteristics might indicate multiple modes of 

origin for fracture belts as well and thus must be accounted for 

in hypotheses of origin for fracture belts.

Like ridged belts, fracture belts also have a complex 

stratigraphy as observed in the north-polar region of Venus. The 

largest fracture belt in the region, Szél-anya Lineae, appears to 

be embayed by various plains units at its southern end, but the 

fractures associated with the northern portion of the belt deform 

all surrounding units. If the plains in this region were emplaced 

during a similar time period, the differing interactions with surrounding units suggest that Szél-anya Lineae was active over an 

extended period of time. The younger, northern portion of Szélanya Lineae interpreted under this assumption is associated with 

localized, small-scale volcanism that embays local fractures, 

suggesting that the tensile stresses in the region may have led to 

volcanism relatively recently in the history of the area. Even if 

the regional plains units formed at different times, with the more 

southerly plains deposits representing younger material and the 

more northerly plains deposits representing older material, leading to the alternative interpretation that the extension associated 

with the formation of the fracture belt occurred during a single 

event, the younger, small-scale volcanism observed at the northern extent of the fracture belt suggests that the northern extent 

of Szél-anya Lineae was active more recently than the southern 

extent.

Regional Plains Units

Dark Deformed Plains Material

Dark deformed plains material (unit pdd, fig. 12A) forms 

relatively smooth, radar dark deposits that exhibit evidence 

of subsequent deformation, generally in the form of polygonal cracking or localized, small-scale wrinkles in the terrain. 

Isolated small mounds interpreted to be shield volcanoes are 

often observed within unit pdd, and clusters of these shield 

volcanoes (mapped as unit psh1) can be seen to superpose 

many of the dark deformed plains materials they border. The 

dark plains unit likely represents a deformed subunit of the dark 

smooth plains unit discussed below, but stratigraphic relations 

between these two units clearly indicate that the latter unit at 

least partially covers the small-scale cracks or wrinkles associated with the deformed plains units, leading to the distinction of 

dark deformed plains unit as a separate, generally older unit. As 

a distinct unit, unit pdd makes up 910 x 103 km2 or 14% of the 

total area of V–1 and appears to be widely distributed throughout V–1, with higher concentrations clustered near the tectonic 

units described above (fig. 1).

Bright Deformed Plains Material

Bright deformed plains material (unit pbd, fig. 12B) is 

generally rougher than unit pdd at a 12.6 cm wavelength scale, 

yielding the observed higher radar backscatter. Like the dark 

deformed plains unit pdd, unit pbd deposits are often characterized by small-scale polygonal cracking or wrinkling of underlying terrain and could represent a deformed subunit of the bright 

smooth plains unit pbs discussed below. Isolated small shield 

volcanoes are also found within these deformed plains units, 

though fewer are observed in unit pbd than in the other plains 

units. Unit pbd covers 780 x 103 km2 or 12% of the total area 

of V–1 and tends to cluster near the dark deformed plains and 

the tectonic units described above.

Dark Smooth Plains Material

Dark smooth plains material (unit pds, fig. 12C) is among 

the smoothest material in the V–1 region at the 12.6-cm wavelength scale and is distinguished by regions of uniformly low 

radar backscatter. Some portions of the dark smooth plains unit 
7

have been deformed by regional tectonic stresses that generated large wrinkle ridges in some locations and grabens in other 

locations that can be traced across the plains, leading previous 

examples of these plains to be defined as part of a wrinkle ridge 

plains unit (unit pwr, Ivanov and Head, 2009), a dark plains unit 

(Squyres and others, 1992a), a smooth plains unit or a plains 

with wrinkle ridges unit (unit pwr Basilevsky and Head, 2000), 

and as the lower unit pwr1 of regional plains (Ivanov and Head, 

2009). However, because the tectonic deformation does not 

obscure the original radar dark material, this unit is mapped as a 

dark smooth plains unit that has been subjected to later tectonic 

activity. The dark smooth plains are concentrated in Snegurochka Planitia (long 200° E.–70° E.) and Louhi Planitia (long 

80° E.–190° E., fig. 1) and make up the most spatially abundant 

unit in V–1, covering 1.5 x 106 km2 or 23% of the total area. 

Some more localized deposits are observed around Klenova 

crater (lat 78.2° N., long 104.7° E.), and while these deposits 

may be linked to the formation of Klenova crater (for example, 

radar-dark parabolas, Campbell and others, 1992; Basilevsky 

and Head, 2000), they are not observed to be a texturally 

distinct unit and are thus not mapped as separate units. Isolated 

shield volcanoes are observed within unit pds, and the greatest 

concentrations of volcanoes are located near the boundaries of 

the smooth plains unit where they generally appear to have been 

covered by dark smooth regional plains deposits.

The dark smooth plains material (unit pds) generally 

superposes all units described thus far. Deformation lineaments 

associated with tessera, ridged belt, densely lineated plains, and, 

on a smaller scale, deformed plains units, tend to be truncated at 

boundaries shared with the dark smooth plains unit, suggesting 

that the smooth plains unit (unit pbs) was emplaced after units 

ta, tb, pdl, pdb, and pbd. Some lineaments associated with fracture belts also are truncated by the dark smooth plains unit, specifically the southern extent of Szél-anya Lineae, though other 

fracture belt lineaments, such as in the northern extent of Szélanya Lineae, cut through nearby deposits of the dark smooth 

plains unit. This observation, in conjunction with observations 

of other deformation structures (specifically, wrinkle ridges and 

lineaments) within dark smooth plains deposits, indicates that 

this region of Venus has continued to be tectonically active after 

the emplacement of the dark smooth plains unit.

Bright Smooth Plains Material

Bright smooth plains material (unit pbs, fig. 12D) has a 

higher radar backscatter suggesting that it has a greater surface 

roughness than the dark smooth plains unit. Similar plains have 

been identified previously as part of the upper unit of regional 

plains with wrinkle ridges (unit pwr2 in Basilevsky and Head, 

2000), but the current characterization describes the original 

unit and interprets superposed features such as wrinkle ridges as 

subsequent tectonic deformation. Bright smooth plains deposits cover 480 x 103 km2 or 7.2% of the total area, and they are 

typically located near boundaries between deformed units and 

stratigraphically younger regional plains units and have outer 

boundaries that are generally characterized by lobate geometries 

(for example, fig. 12D, at the boundary between Fortuna Tessera 

and Snegurochka Planitia, lat 78° N., long 10° E.). Observations 

generally indicate that the bright smooth plains unit superposes 

surrounding materials including the dark smooth plains unit, 

indicating that bright smooth plains deposits comprise the 

youngest regional plains unit observed in the region.

Local Plains Units

Shield Plains Units

Shield plains (units psh1, psh2, fig. 13A) are characterized 

by clusters of small shield-like mounds (1–20 km in diameter) that generally have a radar bright center surrounded by a 

more subdued radar bright apron. Each mound is mapped as 

an individual structure (see fig. 4C, on map), and shield plains 

are mapped as a unit when the aprons, interpreted to be volcanic flows associated with the mounds, overlap or lie in close 

proximity to other aprons (in other words, when they cluster), 

forming a somewhat radar-mottled appearance. Mounds may be 

randomly distributed in a cluster (fig. 14A, on map) or they may 

be aligned along a fracture (fig. 14B, on map). Similar features 

have been identified previously and are mapped as distinct 

units in many other areas on Venus (for example, Basilevsky 

and Head, 1988, 1995; Crumpler and Aubele, 2000; Ivanov and 

Head, 2001, 2009). Outcrops of shield plains units cover 270 

x 103 km2, or 4.1% of the total area within V–1 at generally 

intermediate elevations between deformed materials such as 

the densely lineated plains unit (pdl), ridged belt unit (rb), and 

fracture belt unit (fb) and plains materials such as radar dark 

and bright deformed units and the radar dark smooth plains unit 

(pbd, pdd, pbs, pds; fig. 14A,B, on map). The aprons, or flows, 

appear to cover the more deformed materials such as units t and 

rb and the deformed plains materials such as unit pdl, but the 

aprons appear to be covered by the smoother regional plains 

units pds and pbs in most cases. This indicates that, in general, 

the lower shield plains unit (psh1) formed between episodes 

of deformed regional plains unit emplacement and episodes of 

smooth regional plains emplacement. Shield plains unit psh1

covers 264.6 x 103 km2 or 4.0% of the total area. Two exceptions to this trend in the stratigraphy of shield plains have been 

identified within the region, with one cluster partially covering 

the central caldera of the large shield volcano Renpet Mons (fig. 

14C, lat 77° N., long 235° E., on map) and with the second covering the young fractures observed at the center of the northern 

extent of the fracture belt Szél-anya Lineae (see fig. 21B, on 

map). These two exceptions (unit psh2) indicate that locally, 

conditions required to produce small shield volcanism existed 

relatively recently in the history of this region. This upper shield 

plains unit covers 2.9 x 103 km2 or 0.04% of the total area.

Bright Deformed Corona Plains Material

Bright deformed corona plains material (unit pcbd, fig. 

13B, white arrow) is similar in texture and appearance to bright 

deformed regional plains, with a generally high backscatter 

and small-scale polygonal cracking or wrinkling of underlying terrain observed. Similar units have been identified in 

other regions of Venus and have been mapped, for example, 

as “corona material a” unit coa (V–5, Rosenberg and McGill, 

2001). Deposits of this local bright deformed plains unit in 
8

V–1 are observed to be spatially associated with the exterior 

of coronae in the region and cover 56 x 103 km2 or 0.85% of 

the total area of V–1. These deposits are typically younger than 

annulus unit an and tessera unit ta materials, at least partially 

covering deformation associated with these units. In contrast, 

these deformed coronae plains are generally embayed by 

smooth regional plains materials (units pds, pbs), as the smallscale wrinkles associated with these locally deformed plains 

are truncated at boundaries with these smoother regional plains 

materials.

Dark Smooth Corona Plains Material

Dark smooth corona plains material (unit pcds, fig. 13C) 

is similar in texture and appearance to the dark smooth regional 

plains unit, with uniformly low radar backscatter at the 12.6-cm 

wavelength scale. Deposits of this local dark smooth plains unit 

are observed to be spatially associated with the interior of coronae in the region and occupy 41 x 103 km2 or 0.60% of the total 

area of V–1. The dark smooth plains unit generally superposes 

most of the adjacent units, including annulus unit an, densely 

lineated plains unit pdl, and shield plains unit psh1. Deformation lineaments associated with annulus and densely lineated 

plains units tend to be truncated at boundaries shared with the 

dark smooth plains unit, suggesting that the smooth plains unit 

was emplaced after these other units. Similar units have been 

identified in other regions of Venus and have been mapped, for 

example, as “corona material b” unit cob (V–5, Rosenberg and 

McGill, 2001).

Bright Smooth Corona Plains Material

Bright smooth corona plains material (unit pcbs, fig. 13B, 

black arrow) is similar in texture and appearance to the bright 

smooth regional plains unit, with a higher radar backscatter at 

the 12.6-cm wavelength scale. Similar plains material has been 

identified in other regions of Venus and have been mapped, for 

example, as “corona material c” unit coc (V–5, Rosenberg and 

McGill, 2001). These deposits are generally observed in association with the exterior of coronae in V–1, though at least one 

deposit of unit pcbs flows into the interior of Pomona Corona. 

These deposits cover 190 x 103 km2 or 2.8% of the total area 

in V–1, and observations generally indicate that bright smooth 

plains superpose all surrounding materials including annulus 

unit an materials, densely lineated plains unit pdl, shield plains 

unit psh1, dark smooth regional plains unit pds, and dark 

smooth corona plains unit pcds, indicating that these deposits 

comprise the youngest subunit observed in the region.

Lobate Plains Units

Lobate plains units (pla and plb, fig. 13D,E) have a 

distinctive radial or lateral texture and a radar bright, digitate 

morphology at the outer extents of the deposits. These deposits 

are almost uniformly undeformed by wrinkle ridges and extensional lineaments and are similarly identified in previous mapping efforts as a digitate plains unit (Squyres and others, 1992a) 

and a lobate plains unit (Head and others, 1992). These lobate 

deposits nearly uniformly cover or surround all adjacent units, 

indicating that the lobate plains unit is among the youngest 

units observed in the region. Margins of lobate deposits occur 

within the boundaries of the mapped units, indicating sequential 

episodes of emplacement. These internal margins have been 

designated as flow fronts but not unit boundaries, as the deposits 

in the unit extend beyond the internal flow fronts. There are 

four occurrences of the lobate plains unit within V–1, with three 

locations characterized by material distributed radially around 

a centrally elevated region (covering a total area of 240 x 103

km2 or 3.6% of the region), apparently originating from a point 

source (unit pla), and one location characterized by material 

distributed linearly across surrounding plains (covering a total 

area of 21 x 103 km2 or 0.3% of the region), apparently originating from tensile structural features that deform surrounding 

regional plains materials (unit plb). The radial lobate plains 

deposits tend to be associated with a centralized topographically 

elevated region, including plains associated with Renpet Mons 

(fig. 13D, lat 77° N., long 235° E.), Laka Mons (lat 80° N., long 

265° E.), and Sarasvati Mons (lat 75.5° N., long 353° E.). The 

distribution of the deposits associated with Renpet Mons and 

Laka Mons appear to be nearly radially symmetric, extending 

>250 km and <140 km from the central region, respectively. 

In contrast, the deposits associated with Sarasvati Mons and 

Heloha Fluctus are not radially symmetric, extending almost 

500 km to the northwest but only ~100 km to the southeast 

and northeast and not at all to the southwest. These trends are 

dependent on the topography in the area (see fig. 5, on map). 

The regional plains in the vicinity of Renpet Mons and Laka 

Mons lie at a generally constant elevation of ~500 m and ~200 

m above MPR (6051.8 km), respectively, while the regional 

plains in the vicinity of Sarasvati Mons are confined to a trough 

along the base of a cliff associated with the boundary between 

Iztpapalotl Tessera and Snegurochka Planitia, and these deposits 

follow a regional downward slope of ~0.1% to the northeast. 

These topographic trends are consistent with the observed 

distributions of the lobate plains units. In contrast to these pointsource lobate plains unit materials, the linear lobate plains unit 

materials observed in V–1 (fig. 13E, lat 78° N., long 286° E.) 

appear to be associated with the outer extent of tensile structural 

features that extend from Pomona Corona (lat 79° N., long 300° 

E.), suggesting that these deposits were emplaced by surface 

eruptions from laterally propagating dikes. These deposits of 

lobate plains (unit plb) superpose all surrounding units, indicating that activity related to the development of Pomona Corona 

is younger than activity associated with the development of 

Anahit Corona and with local emplacement of the regional 

plains units.

Edifice Material

Edifice material (unit ed, fig. 13F) consists of distinct 

features characterized by radar bright lines emanating from a 

central high and by radial radar bright, hummocky material at 

larger distances of up to 30–50 km from the feature centers. 

The distinct radar bright lines have been identified previously 

as an effect of radar data of steep slopes, termed layover, in 

which the top of a feature is imaged before the bottom of the 

near-range slope (Ford and others, 1989; Farr, 1993). The 
9

hummocky deposits located on the flanks of the edifice are 

related to flank failure processes, where material deposited 

on the steep edifice slopes collapses and is deposited on the 

surrounding plains materials (Bulmer and Guest, 1996). The 

presence of this effect indicates that these edifices have much 

steeper slopes than typical volcanoes observed on Venus. Three 

edifices were identified on the flanks of Renpet Mons within 

V–1, including Eirene (lat 75.5° N., long 230° E.), Yansa (lat 

76.1° N., long 232.2° E.), and Akka (lat 75.1° N., long 233° 

E.) Tholi, covering a total of 7.6 x 103 km2, or 0.11% of the 

total area. While their spatial extent is limited, edifices have a 

distinct placement in the stratigraphy of the region, apparently 

forming contemporaneously with Renpet Mons as deposits 

associated with the edifices both lie above Renpet Mons flows 

and deflect subsequent flows.

Craters

Undifferentiated Crater Material

Undifferentiated crater material (unit c, see fig. 6, on map, 

table 1) is a unit generally characterized by radar bright material at least partially surrounding a deformed ring that encloses 

a generally radar dark circle and in many cases a central radar 

bright peak. Dark material identified around craters in other 

regions of Venus (for example, Campbell and others, 1992; 

Ivanov and others, 1992; Schultz, 1992; Basilevsky and Head, 

2000; Ivanov and Head, 2009) may surround Klenova crater 

(lat 78.2° N., long 104.7° E.) but is generally not observed or 

mapped in V–1. Details of the morphologies of the twenty-three 

craters identified in V–1 are summarized in table 1 and are 

described in more detail in the General Geology section. Undifferentiated crater material occupies 120 x 103 km2, or 1.7% of 

the total area within V–1.

Structures

Wrinkle Ridges

Wrinkle ridges (fig. 15A) are generally characterized by 

sharp ridges with sharp radar bright peaks that deform underlying terrain and range in length from 0.7 km to 320 km (from 

over 6800 wrinkle ridges mapped). Lengths were measured by 

applying the ArcGIS length calculator to each mapped wrinkle 

ridge, and they represent the complete length of each observed 

wrinkle ridge. Ridges are distinguished from wrinkle ridges 

in that ridges have broader crests rather than sharp peaks, and 

ridges are generally found in isolation, embayed by surrounding 

regional plains units, or in small ridged belts.

There are four main clusters of wrinkle ridges in V–1 (see 

fig. 4, on map): (1) in the dark smooth regional plains surrounding Klenova crater (lat 78.2° N., long 104.7° E.), (2) near 

Lukelong Dorsa (lat 76° N., long 170° E.), (3) on Snegurochka 

Planitia just north of its boundary with Fortuna Tessera (near 

lat 79° N., long 11° E.), and (4) in the regional plains deposits 

surrounding Anahit Corona (lat 77° N., long 280° E.). Upon 

further investigation of Venera 15/16 data in the Magellan data 

gap (long 115° E.–156° E., see fig. 3, on map), the first two sets 

of wrinkle ridges listed appear to be related to each other and 

possibly also to the northernmost extent of Lukelong Dorsa 

(latitudes 76° N. to 77.6° N., longitudes 156° E. to 171° E., continued to the south in V–5, Rosenberg and McGill, 2001) nearly 

due east across the dark smooth regional plains. The wrinkle 

ridges near the topographic boundary between Fortuna Tessera 

and Snegurochka Planitia appear to extend perpendicular to the 

~2.5 km change in elevation, extending to the north and northwest, deforming only the surrounding regional plains units. The 

final set of wrinkle ridges identified appears to radiate to the 

east, northeast, and southwest of Anahit Corona, though they 

are partially embayed by predominantly dark smooth regional 

plains material to the east of the feature. There are also a significant number of wrinkle ridges associated with ridged belts, 

but because these features are contained within the tectonic unit 

rb, they are not mapped as distinct features. Wrinkle ridges in 

general indicate regions of localized compression, and clusters 

of these structures can thus be used to identify temporal and 

spatial episodes of compression within V–1. The distribution of 

these features within V–1 is consistent with global observations, 

with the highest density of wrinkle ridges concentrated in topographically low regional plains units (Bilotti and Suppe, 1999). 

Also, there is not a ring of compressive deformation observed 

along the north boundary of the high elevation regions of Ishtar 

Terra and Itzpapalotl Tessera, consistent with the idea that not 

all major topographic swells formed at the time of wrinkle ridge 

formation (Bilotti and Suppe, 1999).

Simple Ridges

Simple ridges (fig. 15B) are characterized by more prominent, rounded ridge crests. Simple ridges can be clustered, often 

with smaller scale wrinkle ridges, to form distinct geologic units 

such as the ridged belts unit rb. The ridges mapped in the V–1 

region range in length from 2 km to 235 km (from over 400 

mapped ridges) and are typically associated with geologic units 

rb, pdl, and an. Ridges appear to be clustered predominantly 

along the northern and eastern boundaries of the regional plains 

units that form Snegurochka Planitia, in the ridged belt units 

associated with Dennitsa Dorsa, with the annuli units associated with the coronae, and with the densely lineated plains unit 

associated with the northern boundaries of Itzpapalotl Tessera 

(see figs. 1B and 4B).

Lineament Structures

Lineament structures (fig. 15B) are characterized by long, 

linear fractures or fracture segments that cut underlying terrain 

and range in length from 0.4 km to 165.2 km (from nearly 

11,000 fractures mapped). Again, lengths are measured by 

applying the ArcGIS length calculator to each mapped lineament. Fractures can appear as single straight lines or as double 

lines with a radar shadow juxtaposed to a radar bright wall, 

indicating the presence of a trough or graben (for example, 

Head and others, 1991; Solomon and others, 1992; Grosfils and 

Head, 1994; Ernst and others, 2001, 2003). The radar shadow 

lies on the side of the trough that is hidden from incoming radar 

and thus points in the direction from which the incident waves 

arrive.
10

The three most prominent clusters of lineaments are located 

near long 80° E. from lat 75° N. to 85° N. and from long 285° 

E. to 320° E., where lineaments radiate from two central points 

near lat 77° N., long 280° E. and lat 79° N., long 300° E. (see 

fig. 4, on map). The first cluster is closely associated with the 

fracture belt Szél-anya Lineae, and the concentration of fractures 

near lat 84° N., long 95° E. represents the interaction of the 

northern extent of this fracture belt with the surrounding plains 

as the fractures deform underlying material. The second cluster 

of lineaments is associated with Anahit Corona, with the most 

prominent fractures lying to the northwest of the feature, and 

the third, much denser cluster of fractures is associated with the 

nearby Pomona Corona, with fractures lying in every direction 

except to the southeast, where the prominent Itzpapalotl Tessera, where thicker crust likely inhibits the formation of these 

features. The fractures that lie to the west of Pomona Corona are 

covered by radar bright and lobate plains at their outer extents, 

and the presence of these plains units indicate that the fractures 

at this location are likely to be dikes that radiate from Pomona 

Corona. A fourth, more minor cluster of lineaments that is also 

interpreted to be dikes is located near lat 76.7° N., long 181° E., 

where mounds interpreted to be small shield volcanoes form in 

line with fractures that extend into the shield plains unit (psh1) 

from the neighboring densely lineated plains unit (pdl). We interpret that these fissures, identified to be dikes, fed the eruptions 

that formed the small shield volcanoes observed.

Central Peaks

Central peaks (see fig. 6 (on map) and table 1, craters 

9, 15, 19, for example) are typically characterized by a steep 

dome-like structure observed near the center of an impact crater. 

Of the 23 impact craters observed within the V–1 region, 15 

have mapped central peaks; the smallest crater with an identified central peak is Janice (fig. 6 (on map), crater 5, lat 87.3° N., 

long 261.9° E., diameter 11.9 km), and the largest crater with a 

mostly embayed cluster of central peaks is Lagerlof (fig. 6 (on 

map), crater 22, lat 81.2° N., long 285.1° E., diameter 59.8 km).

Steep-sided Domes

Steep-sided domes (fig. 15C) are domes characterized by 

steep edges bounding broad, flat plateaus. Eight steep-sided 

domes have been identified in the V–1 area, all clustered near 

the northern extent of Szél-anya Lineae (lat 84.6° N., long 88.4° 

E.). These domes may represent eruptions of highly viscous 

material (Pavri and others, 1992) and are informally referred 

to as “pancake domes” in the literature (for example, Bridges, 

1995; Stofan and others, 2000). These steep-sided domes are 

observed in deformed regional plains units pdd and pbd that are 

significantly cut by lineaments, and these lineaments alternatively cut and are covered by the steep-sided domes, suggesting 

a concurrent formation for the lineaments and dome structures.

Stratigraphic Relations of Units

The identification and separation of Snegurochka Planitia (V–1) into different units and structures facilitate further 

analysis as to the timing and evolution of geologic activity in 

this north polar region of Venus. The geologic history of this 

region can be constructed by focusing on stratigraphic relations between neighboring units, with specific emphasis placed 

on superposition and crosscutting relations between material 

and structural units (see Correlation of Map Units). Unfortunately, absolute ages cannot be assigned to these stratigraphically mapped material units because of a nearly random spatial 

distribution of impact craters across the surface of Venus (for 

example, Phillips and others, 1992; Campbell, 1999), though 

some suggested localized crater concentrations may support 

several episodes of regional plains emplacement (for example, 

Hauck and others, 1998).

The oldest unit that has consistently been identified in V–1 

as well as the rest of the surface of Venus is tessera, a unit that 

is interpreted to be somewhat analogous to terrestrial mountainous terrain with thickened crust (for example, Bindschadler 

and Head, 1991; Ivanov and Head, 1996; Head and Basilevsky, 

1998; Basilevsky and Head, 2000; Hansen and others, 2000). 

Direct interactions between tessera outcrops and units such 

as dark deformed, dark smooth, and bright smooth regional 

plains, shield plains, and fracture belts indicate that these latter 

units formed after the tessera unit, with plains units covering 

and fractures deforming the heavily deformed tessera unit (for 

example, fig. 16A, on map). Grabens that subsequently deform 

the tessera unit are observed in portions of tessera units within 

V–1, though the more narrow and longer troughs and ridges 

associated with ribbon terrain that is identified elsewhere on 

the planet (for example, Phillips and Hansen, 1998; Hansen 

and Willis, 1998; Hansen and others, 2000) is not observed in 

V–1. These features indicate that tensile stresses resulted in the 

deformation of tessera materials after the initial compressive 

stresses responsible for the formation of these units ceased. 

Other lineaments associated with the densely lineated plains 

unit in Itzpapalotl Tessera appear to have been deformed by 

tessera-associated deformation, possibly indicating a concurrent 

formation (fig. 16B, on map).

The densely lineated plains unit is interpreted to have 

formed next in the sequence observed in V–1. These older 

plains materials are interpreted to be modified by either localized tensile or compressive stresses, depending on whether 

fractures or ridges make up the deformation of the unit, though 

the majority of the densely lineated plains unit appears to have 

formed as the result of compressive stresses. Outcrops of the 

densely lineated plains unit are generally modified by younger 

fractures and embayed by the shield plains, smooth regional 

plains, and lobate plains units, relations that are interpreted 

from observations of fractures cutting across the deformed unit 

pdl and by the smoother units psh1, pds, pbs, pla, and plb

that cover lineaments associated with unit pdl (for example, 

fig. 17, on map). In some isolated locations such as lat 76.8° 

N., long 180° E. (see fig. 14B, on map), the shield plains unit 

appears to form concurrently with the densely lineated plains 

unit, as mounds interpreted to be shield volcanoes form in line 

with fractures that extend from the deformed plains unit into the 

shield plains unit. This relation suggests that these fractures may 

be expressions of subsurface dikes that breached the surface to 

feed localized eruptions and the formation of these shield volca-
11

noes (for example, Head and others, 1996; Jonsson and others, 

1999; Wilson, 2001).

Annulus unit an is also interpreted to form during an 

early geologic period associated with the three coronae features located within V–1 (for example, see fig. 9C). Coronae 

are interpreted to form as a thermal plume ascends, uplifting 

the crust and inducing surface volcanism before collapsing, 

resulting in gravitational relaxation of the crust (for example, 

Pronin and Stofan, 1990; Janes and others, 1992; Squyres and 

others, 1992b; Roberts and Head, 1993; Smrekar and Stofan, 

1997). As the crust is uplifted, the terrain that is pushed outward 

forms concentric ridges that are mapped as the corona annulus 

as well as outcrops of isolated tessera unit ta (lat 79.9° N., long 

292° E.). In the case of Maslenitsa Corona (lat 76.8° N., long 

202.3° E.), the associated annulus unit an and surrounding 

plains units pcbd and pcbs lie adjacent to the ridged belt Dennitsa Dorsa. While the unit rb associated with Dennitsa Dorsa 

appears to be embayed by the northernmost corona plains unit 

pcbs associated with Maslenitsa Corona, the unit rb appears 

to curve around the westernmost unit an of the corona. These 

observations support the theory of extended corona evolution, 

as the annulus unit of Maslenitsa Corona may have formed 

either before or concurrently with Dennitsa Dorsa, forming a 

topographic barrier that diverted the formation of the ridged 

belt unit, and subsequent emplacement of the corona plains 

units covered the older ridged belt. These relations indicate that 

volcanism and extension occurred in multiple episodes over 

extended periods of time to form the feature observed today.

This trend of extended corona formation is also evident in 

Pomona Corona. Localized volcanism occurred early in the evolution of the corona outside the annulus, with the emplacement 

of both regional plains units (pdd, pbd) and the local plains unit 

pcbd. These plains units were subsequently deformed by the 

formation of grabens radiating away from the corona annulus 

(lat 80.4° N., long 303.4° E.) or by the formation of wrinkle 

ridges associated with the continued formation of the corona 

annulus (lat 77.4° N., long 280.5° E.). Subsequent emplacement 

of regional plains units as well as more local plains units surround (pbd, pdd, pbs, pds, pcbs) and fill (unit pcds) the central plateau of the coronae. Materials associated with unit pcbs

associated with Pomona Corona, for example, both cover older 

fractures and are cut by younger fractures that radiate from the 

nearby corona (fig. 18, on map). In the case of Pomona Corona, 

these fractures appear to be the source of the nearby volcanic 

unit plb (see fig. 13C). The volcanic flows postdate features 

associated with the neighboring Anahit Corona, indicating that 

Pomona Corona was active more recently than Anahit Corona 

in this area. Additionally, materials associated with the younger 

local plains units pcbs and pcds are observed in association 

with each corona observed in V–1, with radar bright material 

(unit pcbs) typically covering other regional plains units as well 

as structures that radiate from the coronae, and with radar dark 

material (unit pcds) covering the interior of the corona plateaus. 

Contacts between units pcbs and pcds are rare, but where the 

two units interact in the plateau of Pomona Corona (lat 78.6° 

N., long 299° E.), unit pcbs appears to embay unit pcds. These 

embayment relations support the theory that volcanic activity is 

consistent with late-stage coronae evolution, with the formation 

of units pcbs and plb representing the youngest activity associated with coronae.

Structures within ridged belts appear to deform densely 

lineated plains when these units interact, indicating in general 

a more recent formation age for the ridged belt unit. The ridged 

belt unit is then typically embayed by regional plains units 

pds and pbs and shield plains unit psh1 (for example, fig. 

19A, on map). Prior to analysis of Magellan data, ridged belts 

were interpreted to form due to either regional extension (for 

example, Sukhanov and Schubert, 1989) or regional contraction (for example, Frank and Head, 1990; Kryuchkov, 1990, 

and references therein). Observations of the Magellan data in 

Snegurochka Planitia (V–1) support a contractional origin, as 

the ridged belts appear to be clusters of ridges that have been 

compressed into a belt of deformed material. Topographic 

observations of troughs at the edge of the raised belts of Dennitsa Dorsa and Lukelong Dorsa indicate that contraction and 

even possible underthrusting may occur during the formation of 

these ridged belts (fig. 10; fig. 18 (on map) in Frank and Head, 

1990). Wrinkle ridges parallel to Lukelong Dorsa and fractures 

perpendicular to the wrinkle ridges appear to be associated with 

the formation of ridged belts such as Lukelong Dorsa (fig. 19B, 

on map), with wrinkle ridges trending perpendicular to the most 

compressive stress and fractures propagating parallel to the 

most compressive stress. While similar features near Dennitsa 

Dorsa have possibly been covered by regional plains material, 

the presence of these younger structural lineaments in the vicinity of Lukelong Dorsa might indicate that subsequent regional 

volcanic activity has not yet concealed these tectonic imprints, 

suggesting that several episodes of ridged belt formation might 

be evident in this part of the north polar region of Venus.

These early episodes of intense tectonic activity responsible 

for the deformation of precursor material into tessera, densely 

lineated plains, annuli, and at least some ridged belts, were followed by several episodes of volcanic plains emplacement. Multiple episodes of plains emplacement are evident in the complex 

stratigraphic relations between the four identified regional plains 

units, though absolute time differences cannot be distinguished 

based on these observations. The first episode of regional plains 

emplacement resulted in the deposition of extensive lava flows 

currently observed and mapped as dark and bright deformed 

regional plains units pdd and pbd. These material units are 

defined by small-scale deformation features such as polygonal 

cracks that generally are truncated at boundaries shared with 

other smoother plains units. These stratigraphically younger, 

smoother regional plains units pds and pbs are interpreted to 

be associated with a second episode of regional plains emplacement that occurred later, forming the dark smooth plains unit 

that covers most of the north polar region of Venus (fig. 20A, on 

map). Source vents for these regional plains have not yet been 

identified, and they may be covered by the plains themselves or 

the vents may be below the resolution of the data (75 m/pix). 

The most recent observed episode of regional plains emplacement resulted in the deposition of the bright smooth regional unit 

pbs. Generally, these youngest plains are observed to superpose 

surrounding plains units pdd, pbd, and pds close to topographic 

boundaries such as the boundaries between Fortuna Tessera and 

Snegurochka Planitia and the areas surrounding Tezan Lineae 
12

(lat 84.7° N., long 19.4° E.). Some unit pbs materials may have 

originated from more local point sources along these topographic 

boundaries (fig. 20B, on map), indicating possible late-stage 

volcanism associated with these features, but their consistently 

bright morphology and their lack of a clear central source leads 

to their classification as a regional plains unit.

While observations of these plains unit boundaries indicate 

that several episodes of emplacement are required to yield the 

stratigraphy seen between the different regional plains units, 

these observations cannot be used to assign an absolute time 

elapsed between episodes. In fact, little or no time might have 

elapsed between emplacement events; the stratigraphy may 

indicate different magma or vent sources rather than different 

times. However, the overall trend of emplacement and subsequent modification of the older deformed plains units pdd and 

pbd followed by emplacement of the younger radar dark plains 

unit pds, then the emplacement of radar bright smooth plains 

unit pbs, is observed throughout the region and is thus incorporated into the stratigraphic column.

The lower shield plains unit psh1 was observed to form 

mostly between episodes of emplacement of the deformed and 

smooth regional plains units, with evidence of interactions with 

units of various ages preserved in the V–1 region. These relations were interpreted based on criteria for the stratigraphy of 

the shield plains unit presented by Ivanov and Head (2004a). 

Their stratigraphy with older units is preserved locally, with 

individual shields or shield plains forming on or adjacent to 

previously emplaced tessera, ridged belt, and densely lineated 

plains units (see fig. 17, on map), as well as deformed regional 

plains units (for example, fig. 21A, on map). Lower shield 

plains materials (unit psh1) tend to be preserved at intermediate 

elevations where they generally have been embayed by younger, 

lower lying regional plains units. In some cases, regional plains 

units conceal the radar bright aprons associated with the small 

shields, leaving behind a cluster of peaks that appear to increase 

in size as the embaying plains units decrease in thickness 

with increasing topography (for example, Head and others, 

1992; Kreslavsky and Head, 1999; Ivanov and Head, 2004a). 

The majority of the lower shield plains materials (unit psh1) 

observed in V–1 follow this trend, suggesting that the most 

active time of lower shield plains unit formation occurred after 

the emplacement and subsequent modification of the deformed 

regional plains units but before the emplacement of the smooth 

regional plains units pds and pbs (for example, figs. 14B, 22A, 

on map). In contrast, observations of upper shield plains unit 

psh2 materials cover some of the youngest units in the region, 

including the fracture belt unit associated with Szél-anya Lineae 

(fig. 21B, on map) and the lobate plains unit associated with 

Renpet Mons (see fig. 14C, on map), indicating that younger 

episodes of shield plains formation has occurred. The observations of the two instances of shield plains, (1) unit psh1

deposits that are partially embayed by younger smooth plains 

materials at intermediate elevations and (2) unit psh2 deposits 

that embay relatively young features such as lobate flows and 

fracture belts that embay and deform surrounding deposits, 

respectively, indicate that shield plains formed in at least two 

stratigraphically distinct episodes in the geologic history of this 

region.

The youngest units mapped in the north polar region of 

Venus include some fracture belts (unit fb), lobate plains (unit 

pl), edifices (unit ed), and local smooth radar dark and bright 

plains units associated with late-stage coronae development 

(units pcds, pcbs). Fracture belts such as Szél-anya Lineae 

appear to have formed over extended periods of time, with some 

areas showing evidence of embayment of regional plains units 

(fig. 22A, on map) while others clearly cut through the surrounding plains unit material (see fig. 21B, on map). The outcrops 

of the fracture belt unit that have been embayed appear to be 

tectonically stable, as subsequent fracturing associated with the 

fracture belt unit has not continued after the emplacement of surrounding material. In contrast, the areas that appear younger than 

the surrounding plains units appear to have been active more 

recently than surrounding units, with associated fracturing and 

local volcanism cutting and covering all adjacent materials. A 

local concentration of volcanism occurs in the form of a cluster 

of small shield volcanoes near the center of the more recently 

active northern portion of Szél-anya Lineae. Because Szél-anya 

Lineae extends well beyond the region of more recent volcanic 

activity, the shield plains unit may represent passive magmatic 

activity where magma ascends through pre-fractured terrain 

created by the fracture belt unit. In contrast, the fracture belt 

unit associated with Laka Mons (lat 80° N., long 265° E., fig. 

22B, on map) is a more local feature, extending only ~200 km 

as compared to the >1200 km length of Szél-anya Lineae, and it 

has a large shield volcano situated near the center of the belt. In 

this case, the fracture belt unit may have formed as a result of an 

actively ascending magma plume that also acted as the source 

for the eruptions that resulted in the formation of Laka Mons. 

The lobate plains unit associated with this volcano extends over 

the surrounding plains units, completely covering wrinkle ridges 

that deform the plains immediately adjacent to Laka Mons where 

the lava flows are interpreted to be thicker, and at least partially 

covering wrinkle ridges that deform the plains near the distal 

extent of the lobate plains where the flows are interpreted to be 

thinner. The stratigraphic trend that the observed lobate flows 

unit is stratigraphically the youngest feature observed is also 

consistent with observations of unit pla associated with Renpet 

Mons and Sarasvati Mons overlying other adjacent units.

While the lobate plains unit associated with Renpet Mons 

also covers surrounding plains units, unit pla has a somewhat 

more complex interaction with other volcanic units that lie on 

the flanks of this large volcano, including the edifice and shield 

plains units ed and psh2 (fig. 23, on map). Three outcrops 

of the edifice unit are observed within V–1, including Eirene, 

Yansa, and Akka Tholi (as well as Thallo Mons that lies in the 

neighboring V–5 quadrangle, Rosenberg and McGill, 2001), 

and these features lie on the western side of Renpet Mons and 

appear to have formed concurrently with the unit pla materials 

from the larger shield volcano. Flows associated with Renpet 

Mons apparently form the foundation upon which the three 

smaller edifices lie, but later flows from Renpet Mons clearly 

are diverted by these smaller volcanoes. These observations 

indicate that Renpet Mons erupted several times, forming 

its present structure before the smaller edifices formed on its 

flanks. After the edifices formed, Renpet Mons continued to 

erupt, feeding flows that flowed around the newer volcanoes. 
13

The youngest volcanism in this area appears to be a cluster 

of small shields near the caldera of the large shield volcano, 

shields that fed flows covering the southeast section of the 

caldera.

An outcrop of lobate plains material, unit plb, is observed 

between Anahit Corona and Pomona Corona (fig. 18, on map). 

This unit appears to originate from linear fissure sources associated with Pomona Corona as opposed to a central source such 

as that observed with Renpet Mons, for example. These local 

flows superpose the surrounding regional plains units as well 

as the deformed materials associated with the corona annulus 

unit. Other plains units associated with all coronae observed 

in V–1 include smooth, radar dark and radar bright coronae 

units (pcds, pcbs). These units are interpreted to form towards 

the final stages of coronae evolution, with the dark plains unit 

forming in the center of the raised corona plateau and the bright 

plains unit forming at the outer edges of the corona annulus 

unit. The deposition of the radar bright smooth coronae plains 

unit may be coeval with and (or) postdate the lobate plains unit 

associated with dikes that radiate from Pomona Corona (fig. 18, 

on map), though adjacent boundaries between these two units 

are not prevalent and thus these interpretations are not conclusive. The deposition of the radar dark smooth coronae plains 

unit occurred after the formation of the annulus and densely 

lineated plains units associated with the coronae, a trend that is 

apparent where deformation associated with these latter units 

is truncated at boundaries with the radar dark coronae plains 

unit. The superposition of these young flows over older coronae 

materials (for example, units an, pdl, ta) observed in the region 

indicates that the coronae formed over extended periods of time, 

consistent with other observations of coronae evolution (that is, 

Pronin and Stofan, 1990; Roberts and Head, 1993). The relatively young age of these flows indicates that coronae represent 

some of the most recently active features within V–1.

Geologic History

The stratigraphy described above indicates that the observable geologic history of the north polar region of Venus can 

be characterized by a sequence of stress states that alternates 

between compressive and tensile. This sequence is consistent 

with interpretations for the most recent 10-20% of the geologic 

history of Venus in general, over which time deformation associated with the formation of tessera, followed by dense fracturing, 

then broad wrinkle ridging, and, finally, localized fracturing 

indicates a series of successive tectonic episodes consistent 

with first compressive, then tensile, then again compressive, 

and, finally, tensile stresses (for example, Basilevsky and Head, 

1998; Head and Basilevsky, 1998; Basilevsky and Head, 2000). 

Overall activity and intensity of these tectonic episodes appears 

to decline over time as deformation resulting from each episode 

becomes more localized. The earliest activity observed in the 

Snegurochka Planitia (V–1) region consisted of the formation of 

tessera, a feature that is generally considered to have formed by 

early stages of compression-induced deformation such as folds 

and raised topography, followed by tension-induced deformation such as grabens and ribbons within the now folded terrain 

(for example, Bindschadler and Head, 1991; Ivanov and Head, 

1996; Hansen and Willis, 1998). This early compressive environment may have been the result of a combination of many factors 

including, for example, mantle overturn (for example, Parmentier and Hess, 1992), mantle convection (for example, ArkaniHamed, 1993; Phillips and Hansen, 1994), or episodic plate 

tectonics (for example, Turcotte, 1993). Alternative hypotheses 

for tessera formation include crustal thickening as the result of 

upwelling in a mantle plume (Hansen and others, 1997; Hansen 

and Willis, 1998), possibly resulting in the formation of a lava 

pond on the surface that cooled to form the observed tessera 

terrain (Hansen, 2006), though proposed evidence for these 

hypotheses is observed in Lakshmi Planitia (V–7), outside the 

Snegurochka Planitia (V–1) region. Also forming during an early 

stage of compression are densely lineated plains and ridged belts. 

Ridged belts in particular have been identified as compressional 

features that formed in response to the shortening of terrain due 

to regional stresses. In some locations, such as Lukelong Dorsa, 

crustal shortening leads to flexure and possible under-thrusting 

of plains and to the formation of a trough that runs parallel to the 

folded ridged belt (for example, Frank and Head, 1990). Observations indicate that ridged belt formation primarily occurred 

during this earlier period of regional compression, though some 

features such as Lukelong Dorsa may have been reactivated in a 

later episode of regional compression.

The next period of geologic activity involves the emplacement of the various episodes of regional and shield plains 

materials and is thus interpreted to represent a broad tensile 

stress field. While the regional deformed and radar dark smooth 

plains units are likely similar to flood basalts, individual source 

vents for the more localized radar bright smooth plains units 

have yet to be identified. We observe that these vents will take 

on the form of small vents and fissures that were either subsequently covered by the volcanic plains or are too small to be 

identified with available data. These interpreted fissures would 

have resulted from regional tensile stresses, feeding widespread 

volcanism at rates on the order of a few km3 y-1 (for example, 

Basilevsky and Head, 1996). These episodes of regional plains 

emplacement are stratigraphically distinct, but with such high 

extrusion rates they may have been emplaced within a relatively 

short period of time (10–100 m.y.) in the geologic history of 

Venus (that is, Herrick, 1994; Strom and others, 1994; Basilevsky and Head, 1996).

Additional evidence for extension during this period is 

observed in fissures associated with coronae. Many fissures 

associated with Anahit Corona and Maslenitsa Corona have 

been at least partially covered by subsequent regional plains 

emplacement, indicating that these fissures formed throughout 

this earlier period of regional volcanic activity. Corona annuli 

may also have formed during this time in the history of V–1 

before being subsequently embayed by continued emplacement 

of regional plains. The end of this period marks the end of widespread regional volcanism observed in this region of Venus, an 

observation that is consistent with interpretations of volcanism 

for the rest of the planet (for example, Basilevsky and Head, 

1998), indicating a broad shift in volcanic activity at this time in 

the geologic history of Venus.
14

The plains emplaced during this time were subsequently 

subjected to compressive tectonic deformation during the next 

period of geologic activity. The stresses that characterize this 

compressive period are thought to have been more localized, 

as the wrinkle ridges that are interpreted to have formed during 

this period are concentrated primarily within Louhi Planitia 

and possibly coincide with a reactivation of ridged belt formation in Lukelong Dorsa. This period is interpreted to have been 

relatively brief or of low intensity, as the wrinkle ridges locally 

deform a single unit (dark smooth regional plains), suggesting 

that the stress field was not strong enough to deform older, more 

stable material such as tessera or ridged belts, nor was it present 

for enough time to deform younger material such as fracture 

belts, lobate plains, or the youngest shield plains that were 

emplaced later.

The most recent observed period of geologic activity shifts 

to a tensile stress regime and is characterized by fracture belt 

formation and volcanism associated with large shield volcanoes and coronae, with localized extension occurring both in 

Louhi Planitia with the formation of Szél-anya Lineae and in 

Snegurochka Planitia with the formation of Renpet Mons, Laka 

Mons, and the continued formation of Pomona Corona. While 

some volcanism may have resulted from passive ascent through 

pre-fractured terrain (for example, the shield plains present 

at the northern extent of Szél-anya Lineae), other volcanism 

likely occurred due to the active ascent of a magma plume (for 

example, Renpet Mons, Laka Mons, and fissures associated 

with Pomona Corona). These observations and interpretations indicate that magma plumes and rifting were active more 

recently than other processes observed in this region.

The geologic history described above closely mirrors 

many interpretations for the geologic history of Venus as a 

whole (Basilevsky and Head, 1995; Basilevsky and others, 

1997). Observations made in this quadrangle do not support an 

alternative interpretation of the geologic history of Venus that 

involves a more random temporal distribution of feature formation, with features such as coronae, rifts, large and small shield 

volcanoes, and regional volcanic plains forming throughout the 

history of the region (that is, Guest and Stofan, 1999). While 

the periods of compressive and tensile activity are not correlated to terrestrial events, they appear to have occurred globally 

on Venus as well as on the Moon, Mercury, and Mars (Head 

and Solomon, 1981). Further investigations and modeling may 

indicate that early Earth underwent similar periods of activity, 

but as Earth developed plate tectonics and an oxygen-enriched 

atmosphere, the geologic history of the Earth diverged from 

that of Venus. By continuing to study the stratigraphy of Venus, 

we may be better equipped to understand the early evolution 

of the Earth and why the later geologic histories of the two 

planets differ.

References Cited

Arkani-Hamed, J., 1993, On the thermal evolution of Venus: 

Journal of Geophysical Research, v. 99, no. E1, p. 2019–

2033.

Arvidson, R.E., Plaut, J.J., Jurgens, R.F., and 2 others, 1990, 

Geology of Southern Guinevere Planitia, Venus, Based on 

analysis of Goldstone radar data: 20th Lunar and Planetary 

Science Conference, p. 557–572.

Arvidson, R.E., Baker, V.R., Elachi, C., and 2 others, 1991, 

Magellan: Initial analysis of Venus surface modification: 

Science, v. 252, p. 270–275.

Baker, V.R., Komatsu, G., Parker, T.J., Gulick, and 3 others, 

1992, Channels and valleys on Venus—Preliminary analysis of Magellan data: Journal of Geophysical Research, v. 

97, no. E8, p. 13,421–13,444.

Barsukov, V.L., 1986, Basilevsky, A.T., Burba, G.A., Bobina, 

N.N., and 29 others, The geology and geomorphology of 

the Venus surface as revealed by the radar images obtained 

by Veneras 15 and 16: 16th Lunar and Planetary Science 

Conference, p. 378–398.

Basilevsky, A.T., 1986, Structure of central and eastern areas 

of Ishtar Terra and some problems of Venusian tectonics: 

NASA Tech. Memo., TM-88508, translated from Geotektonika, 1986, v. 20, p. 282–288.

Basilevsky, A.T., 2008, Geologic map of the Beta Regio Quadrangle (V–17), Venus: U.S. Geological Survey Geologic 

Investigations Series Map I–3023, scale 1:5,000,000.

Basilevsky, A.T., and Head, J.W., 1988, The geology of Venus: 

Annual Review of Earth and Planetary Sciences, v. 16, p. 

295–317.

Basilevsky, A.T., and Head, J.W., 1995, Regional and global 

stratigraphy of Venus—A preliminary assessment and 

implications for the geological history of Venus: Planetary 

and Space Science, v. 43, p. 1523–1553.

Basilevsky, A.T., and Head, J.W., 1996, Evidence for rapid and 

widespread emplacement of volcanic plains on Venus—

Stratigraphic studies in the Baltis Vallis Region: Geophysical Research Letters, v. 23, no. 12, p. 1497-1500.

Basilevsky, A.T., and Head, J.W., 1998, The geologic history 

of Venus—A stratigraphic view: Journal of Geophysical 

Research, v. 103, no. E4, 8531–8544.

Basilevsky, A.T., and Head, J.W., 2000, Geologic units on 

Venus—Evidence for their global correlation: Planetary 

and Space Science, v. 48, no. 1, p. 75–111.

Basilevsky, A.T., Head, J.W., Schaber, G.G., and Strom, R.G., 

1997, The resurfacing history of Venus, in Bougher, S.W., 

Hunten, D.M., and Philips, R.J., eds., Venus II: Geology, 

Geophysics, Atmosphere, and Solar Wind Environment: 

University of Arizona Press, p. 1047.

Basilevsky, A.T., Pronin, A.A., Ronca, L.B., and 3 others, 1986, 

Styles of tectonic deformations on Venus—Analysis of 

Venera 15 and 16 data: 16th Lunar and Planetary Science 

Conference, 399–411.

Bilotti, F., and Suppe, J., 1999, The global distribution of 

wrinkle ridges on Venus: Icarus, v. 139, p. 137–157.

Bindschadler, D.L., 1995, Magellan—A new view of Venus’ 

geology and geophysics: Reviews of Geophysics, v. 33, p. 

459-468.

Bindschadler, D.L., and Head, J.W., 1991, Tessera terrain, 

Venus—Characterization and models for origin and evolution: Journal of Geophysical Research, v. 96, no. B4, p. 

5889–5907.
15

Bindschadler, D.L., and Parmentier, E.M., 1990, Mantle flow 

tectonics: The influence of a ductile lower crust and implications for the formation of topographic uplands on Venus: 

Journal of Geophysical Research, v. 95, p. 21,329–21,344.

Bindschadler, D.L., Schubert, G., and Kaula, W.M., 1990, 

Mantle flow tectonics and the origin of Ishtar Terra, Venus: 

Geophysical Research Letters, v. 17, p. 1345–1348.

Bridges, N.T., 1995, Submarine analogs to Venusian pancake 

domes: Geophysical Research Letters, v. 22, no. 20, p. 

2781-2784.

Bridges, N.T., and McGill, G.E., 2002, Geologic map of the 

Kaiwan Fluctus Quadrangle (V–44), Venus: U.S. Geological Survey Geologic Investigations Series Map I–2747, 

scale 1:5,000,000.

Bulmer, M.H., and Guest, J.E., 1996, Modified domes and 

associated debris apron on Venus, in McGuire, J.W., Jones, 

A.P., and Neuberg, J., eds., Volcano instability on the Earth 

and other planets: Geological Society Special Publication, 

v. 110, p. 349–371.

Campbell, B.A., 1999, Surface formation rates and impact 

crater densities on Venus: Journal of Geophysical 

Research, v. 104, no. E9, p. 21,951–21,956.

Campbell, B.A., and Campbell, P.G., 2002, Geologic map of 

the Bell Regio Quadrangle (V–9), Venus: U.S. Geological 

Survey Geologic Investigations Series Map I–2743, scale 

1:5,000,000.

Campbell, D.B., and Burns, B.A., 1980, Earth-based radar 

imagery of Venus: Journal of Geophysical Research, v. 85, 

p. 8271–8281.

Campbell, D.B., Stacy, N.J.S., Newman, W.I., and 5 others, 

1992, Magellan observations of extended impact crater 

related features on the surface of Venus: Journal of Geophysical Research, v. 97, no. E10, p. 16,249–16,277.

Crumpler, L.S., and Aubele, J.C., 2000, Volcanism on Venus, 

in Sigurdsson, H., (ed.), Encyclopedia of volcanoes: San 

Diego, Academic Press, p. 727–769.

Ernst, R.E., Desnoyers, D.W., Head, J.W., and Grosfils, E.B., 

2003, Graben-fissure systems in Guinevere Planitia and 

Beta Regio (264°–312° E., 24°–60° N.), Venus, and 

implications for regional stratigraphy and mantle plumes: 

Icarus, v. 164, p. 282–316.

Ernst, R.E., Grosfils, E.B., and Mége, D., 2001, Giant dike 

swarms—Earth, Venus, and Mars: Annual Review of Earth 

and Planetary Sciences, v. 29, p. 489.

Farr, T.G., 1993, Radar interactions with geologic surfaces, in

Ford, J.P., and 7 others, (eds.), Guide to Magellan Image 

Interpretation: Pasadena, Calif., JPL and California Institute of Technology Publication 93-24, p. 45–56.

Frank, S.L., and Head, J.W., 1990, Ridge belts on Venus—Morphology and origin: Earth, Moon, and Planets, v. 50–51, 

no. 1, p. 421–470.

Ford, J.P., Blom, R.G., Crisp, J.A., and 6 others, 1989, Spaceborne radar observations—A guide for Magellan radarimage analysis: Pasadena, Calif., JPL and California 

Institute of Technology Publication 89–41.

Ford, J.P., Plaut, J.J., Weitz, C.M., and 5 others, 1993, Guide to 

Magellan image interpretation: Pasadena, Calif., JPL and 

California Institute of Technology Publication 93–24.

Ford, P.G., and Pettengill, G.H., 1992, Venus topography and 

kilometer-scale slopes: Journal of Geophysical Research, v. 

97, E8, p. 13,103–13,114.

Greeley, R., Bender, K., Thomas, P.E., and 3 others, 1995, 

Wind-related features and processes on Venus—Summary 

of Magellan results: Icarus, v. 115, no. 2, p. 399–420.

Grosfils, E.B., and Head, J.W., 1994, Emplacement of a radiating dike swarm in western Vinmara Planitia, Venus—

interpretation of the regional stress field orientation and 

subsurface magmatic configuration: Earth, Moon, and 

Planets, v. 66, p. 153–171.

Guest, J.E., and Stofan, E.R., 1999, A new view of the stratigraphic history of Venus: Icarus, v. 139, no. 1, p. 55–66.

Hansen, V.L., 2006, Geologic constraints on crustal plateau 

surface histories, Venus—The lava pond and bolide impact 

hypotheses: Journal of Geophysical Research—Planets, v. 

111, doi:10.1029/2006JE002714.

Hansen, V.L., Phillips, R.J., Willis, J.J., and Ghent, R.R., 2000, 

Structures in tessera terrain, Venus—Issues and answers: 

Journal of Geophysical Research, v. 105, no. E2, p. 

4135–4152.

Hansen, V.L., and Willis, J.J., 1998, Ribbon terrain formation, 

southwestern Fortuna Tessera, Venus—Implications for 

lithosphere evolution: Icarus, v. 132, no. 2, p. 321–343.

Hansen, V.L., Willis, J.J., and Banerdt, W.B., 1997, Tectonic 

overview and synthesis, in Bougher, S.W., Hunten, D.M., 

and Phillips, R.J., eds., Venus II—Geology, Geophysics, 

Atmosphere, and Solar Wind Environment: University of 

Arizona Press, p. 797–844.

Hauck, S.A., II, Phillips, R.J., and Price, M.H., 1998, Venus—

Crater distribution and plains resurfacing models: Journal 

of Geophysical Research, v. 103, no. E6, p. 13,635–13,642.

Head, J.W., and Basilevsky, A.T., 1998, Sequence of tectonic 

deformation in the history of Venus—Evidence from 

global stratigraphic relationships: Geology, v. 26, no. 1, p. 

35–38.

Head, J.W., Campbell, D.B., Elachi, C.H.A.R., and 5 others, 

1991, Venus volcanism—Initial analysis from Magellan 

Data: Science, v. 252, p. 276–288.

Head, J.W., Crumpler, L., Aubele, J., and 2 others, 1992, Venus 

volcanism—Classification of volcanic features and structures, associations, and global distribution from Magellan 

data: Journal of Geophysical Research, v. 97, no. E8, p. 

13,153–13,197.

Head, J.W., and Solomon, S.C., 1981, Tectonic evolution of the 

terrestrial planets: Science, v. 213, p. 62–76.

Head, J.W., Wilson, L., and Smith, D.K., 1996, Mid-ocean ridge 

eruptive vent morphology and substructure—Evidence for 

dike widths, eruption rates, and evolution of eruptions and 

axial volcanic ridges: Journal of Geophysical Research, v. 

101, no. B12, p. 28,265–28,280.

Herrick, R.R., 1994, Resurfacing history of Venus: Geology, v. 

22, no. 8, p. 703–706.

Ivanov, M.A., and Head, J.W., 1996, Tessera terrain on Venus—

A survey of the global distribution, characteristics, and 

relation to surrounding units from Magellan data: Journal 

of Geophysical Research, v. 101, no. E6, p. 14,861–14,908.

Ivanov, M.A., and Head, J.W., 2001, Geology of Venus—Map-
16

ping of a global geotraverse at 30oN latitude: Journal of 

Geophysical Research, v. 106, no. E8, p. 17,515–17,566.

Ivanov, M.A., and Head, J.W., 2004a, Stratigraphy of small 

shield volcanoes on Venus—Criteria for determining stratigraphic relationships and assessment of relative age and 

temporal abundance: Journal of Geophysical Research, v. 

109, doi: 10.1029/2004JE002252.

Ivanov, M.A., and Head, J.W., 2004b, Geologic map of the 

Atalanta Planitia Quadrangle (V–4), Venus: U.S. Geological Survey Geologic Investigations Map I–2792, scale 

1:5,000,000.

Ivanov, M.A., and Head, J.W., 2008, Geologic map of the 

Meskhent Tessera Quadrangle (V–3), Venus: U.S. Geological Survey Scientific Investigations Map 3018, scale 

1:5,000,000.

Ivanov, M.A., and Head, J.W., 2009, Geologic map of the Lakshmi Planum Quadrangle (V–7), Venus: U.S. Geological 

Survey USGS Scientific Investigations Map 3116.

Ivanov, B.A., Nemchinov, I.V., Svetsov, V.A., and 3 others, 

1992, Impact cratering on Venus—Physical and mechanical models: Journal of Geophysical Research, v. 97, no. 

E10, p. 16,167–16,181.

Janes, D.M., Squyres, S.W., Bindschadler, D.L., and 4 others, 

1992, Geophysical models for the formation and evolution 

of coronae on Venus: Journal of Geophysical Research, v. 

97, no. E10, p. 16,055–16,067.

Jonsson, S., Zebker, H., Cervelli, P., and 4 others, 1999, A 

shallow-dipping dike fed the 1995 flank eruption at Fernandina volcano, Galapagos, observed by satellite radar 

interferometry: Geophysical Research Letters, v. 26, no. 8, 

p. 1077–1080.

Jurgens, R.F., Franck, C., Greiner, W., and 6 others, 1990, Radar 

observations of Tinatin Planitia—Goldstone 1988 observations of Venus: 21st Lunar and Planetary Science Conference, p. 593.

Jurgens, R.F., Goldstein, R.M., Rumsey, H.R., and Green, R.R., 

1980, Images of Venus by three-station radar interferometry, 1977 results: Journal of Geophysical Research, v. 85, 

no. A13, p. 8282–8294.

Kargel, J.S., Komatsu, G., Baker, V.R., and Strom, R.G., 1993, 

The volcanology of Venera and VEGA landing sites 

and the geochemistry of Venus: Icarus, v. 103, no. 2, p. 

253–275.

Kaula, W.M., 1995, Venus reconsidered: Science, v. 270, p. 

1460–1464.

Kaula, W.M., Owen, T., Runcorn, S.K., and Tozer, D.C., 1994, 

The tectonics of Venus [and discussion]: Philosophical 

Transactions: Physical Sciences and Engineering, v. 349, p. 

345–355.

Kotelnikov, V.A. and 15 others, 1989, Atlas of Venus: Moscow, 

former Soviet Union (in Russian).

Kozak, R.C., and Schaber, G.G., 1986, Gravity-spreading origin 

of the Venusian tessera: 17th Lunar and Planetary Science 

Conference, p. 444–445.

Kreslavsky, M.A., and Head, J.W., 1999, Morphometry of small 

shield volcanoes on Venus—Implications for the thickness 

of regional plains: Journal of Geophysical Research, v. 

104, p. 18,925–18,932.

Kryuchkov, V.P., 1990, Ridge belts—Are they compressional or 

extensional structures?: Earth Moon and Planets, v. 50-51, 

p. 471–491.

Masursky, H., Eliason, E., Ford, P.G., and 4 others, 1980, 

Pioneer Venus radar results—Geology from images and 

altimetry: Journal of Geophysical Research, v. 85, no. A13, 

p. 8232–8260.

McGill, G.E., 2000, Geologic map of the Sappho Patera Quadrangle (V–20), Venus: U.S. Geological Survey Geologic 

Investigations Series Map I–2637, scale 1:5,000,000.

Namiki, N., and Solomon, S.C., 1994, Impact crater densities on 

volcanoes and coronae on Venus—Implications for volcanic resurfacing: Science, v. 265, p. 929–933.

Nimmo, F., and McKenzie, D., 1998, Volcanism and tectonics 

on Venus: Annual Review of Earth and Planetary Sciences, 

v. 26, no. 1, p. 23.

Parmentier, E.M., and Hess, P.C., 1992, Chemical differentiation of a convecting planetary interior—Consequences for 

a one plate planet such as Venus: Geophysical Research 

Letters, v. 19 no. 20, p. 2015–2018.

Pavri, B., Head, J.W. III, Klose, K.B., and Wilson, L., 1992, 

Steep-sided domes on Venus—Characteristics, geologic 

setting, and eruption conditions from Magellan data: 

Journal of Geophysical Research, v. 97, no. E8, p. 13,445–

13,478.

Pettengill, G.H., Eliason, E., Ford, P.G., and 3 others, 1980, 

Pioneer Venus radar results, altimetry, and surface properties: Journal of Geophysical Research, v. 85, no. A13, p. 

8261–8270.

Phillips, R.J., Arvidson, R.E., Boyce, J.M., and 4 others, 1991, 

Impact craters on Venus—Initial analysis from Magellan: 

Science, v. 252, p. 288–297.

Phillips, R.J., and Hansen, V.L., 1994, Tectonic and magmatic 

evolution of Venus: Annual Review of Earth and Planetary 

Sciences, v. 22, no. 1, p. 597–656.

Phillips, R.J., and Hansen, V.L., 1998, Geological evolution of 

Venus—Rises, plains, plumes, and plateaus: Science, v. 

279, p. 1492–1497.

Phillips, R.J., Raubertas, R.F., Arvidson, R.E., and 4 others, 

1992, Impact craters and Venus resurfacing history: Journal 

of Geophysical Research, v. 97, no. E10, p. 15,923–15,948.

Plaut, J.J., and Arvidson, R.E., 1992, Comparison of Goldstone 

and Magellan radar data in the equatorial plains of Venus: 

Journal of Geophysical Research, v. 97, p. 16,279–16,291.

Pronin, A.A., 1986, The structure of Lakshmi Planum, an 

indication of horizontal asthenospheric flows on Venus: 

Geotectonics, v. 20, p. 271–281.

Pronin, A.A., and Stofan, E.R., 1990, Coronae on Venus—Morphology, classification, and distribution: Icarus, v. 87, no. 

2, p. 452–474.

Roberts, K.M., and Head, J.W., 1993, Large-scale volcanism 

associated with coronae on Venus—Implications for formation and evolution: Geophysical Research Letters, v. 20, 

no. 12, p. 1111–1114.

Rosenberg, E., and McGill, G.E., 2001, Geologic map of the 

Pandrosos Dorsa Quadrangle (V–5), Venus: U.S. Geological Survey Geologic Investigations Series Map I–2721, 

scale 1:5,000,000.
17

Saunders, R.S., Spear, A.J., Allin, P.C., and 24 others, 1992, 

Magellan mission summary: Journal of Geophysical 

Research, v. 97, no. E8, p. 13,067–13,090.

Schaber, G.G., Strom, R.G., Moore, H.J., and 7 others, 1992, 

Geology and distribution of impact craters on Venus—

What are they telling us?: Journal of Geophysical 

Research, v. 97, no. E8, p. 13,257–13,301.

Schultz, P.H., 1992, Atmospheric effects on ejecta emplacement 

and crater formation on Venus from Magellan: Journal of 

Geophysical Research, v. 97, no. E10, p. 16,183–16,248.

Simons, M., Solomon, S.C., and Hager, B.H., 1997, Localization of gravity and topography—Constraints on the tectonics and mantle dynamics of Venus: Geophysical Journal 

International, v. 131, p. 24–31.

Smerkar, S.E., and Phillips, R.J., 1988, Gravity-driven deformation of the crust of Venus: Geophysical Research Letters, v. 

15, p. 693–696.

Smrekar, S.E., and Stofan, E.R., 1997, Corona formation and 

heat loss on Venus by coupled upwelling and delamination: 

Science, v. 277, p. 1289–1294.

Solomon, S.C., 1993, A tectonic resurfacing model for Venus: 

24th Lunar and Planetary Science Conference, p. 1331–

1332.

Solomon, S.C., Smrekar, S.E., Bindschadler, D.L., and 8 others, 

1992, Venus tectonics—An overview of Magellan observations: Journal of Geophysical Research, v. 97, no. E8, p. 

13,199–13,255.

Squyres, S.W., Janes, D.M., Baer, G., and 4 others, 1992b, The 

morphology and evolution of coronae on Venus: Journal of 

Geophysical Research, v. 97, no. E8, p. 13,611–13,634.

Squyres, S.W., Jankowski, D.G., Simons, M., and 3 others, 

1992a, Plains tectonism on Venus—The deformation belts 

of Lavinia Planitia: Journal of Geophysical Research, v. 

97, no. E8, p. 13,579–13,599.

Stofan, E.R., and Guest, E.G., 2003, Geologic map of the Aino 

Planitia Quadrangle (V–46), Venus: U.S. Geological 

Survey Geologic Investigations Series Map I–2779, scale 

1:5,000,000.

Stofan, E.R., and Head, J.W., 1990, Coronae of Mnemosyne 

Regio—Morphology and origin: Icarus, v. 83, no. 1, p. 

216–243.

Stofan, E.R., Head, J.W., Campbell, D.B., and 5 others, 1989, 

Geology of a rift zone on Venus—Beta Regio and Devana 

Chasma: Geological Society of America Bulletin, v. 101, 

no. 1, p. 143–156.

Stofan, E.R., Anderson, S.W., Crown, D.A., and Plaut, J.J., 

2000, Emplacement and composition of steep-sided domes 

on Venus: Journal of Geophysical Research, v. 105, no. 

E11, p. 26,757–26,771.

Stofan, E.R., Sharpton, V.L., Schubert, G., and 4 others, 1992, 

Global distribution and characteristics of coronae and 

related features on Venus—Implications for origin and 

relation to mantle processes: Journal of Geophysical 

Research, v. 97, no. E8, p. 13,347–13,378.

Strom, R.G., Schaber, G.G., and Dawson, D.D., 1994, The 

global resurfacing of Venus: Journal of Geophysical 

Research, v. 99, no. E5, p. 13,899–13,926.

Sukhanov, A.L., 1986, Parquet—Regions of areal plastic dislocations: Geotectonics, v. 20, p. 294–305.

Sukhanov, A.L., 1992, Tesserae, in Venus geology, geochemistry, and geophysics—Research results from the USSR: 

Tucson, Ariz., University of Arizona Press, p. 82–95.

Sukhanov, A.L., and Schubert, G., 1989, Ridged belts on Venus 

as extensional features: 19th Lunar and Planetary Science 

Conference, p. 335–348.

Surkov, Y., Moskalyova, L.P., Kharyukova, V.P., and 3 others, 

1986, Venus rock composition at the Vega 2 landing 

site: Journal of Geophysical Research, v. 91, no. B13, p. 

215–218.

Tanaka, K.L., 1994, Venus geologic mappers’ handbook, 2d ed.: 

U.S. Geological Survey Open-File Report 94–438, p. 50.

Turcotte, D.L., 1993, An episodic hypothesis for Venusian 

tectonics: Journal of Geophysical Research, v. 98, no. E9, 

p. 17,061–17,068.

Tyler, G.L., Simpson, R.A., Maurer, M.J., and Holmann, E., 

1992, Scattering properties of the Venusian surface—Preliminary results from Magellan: Journal of Geophysical 

Research, v. 97, no. E8, p. 13,115–13,139.

Wilhelms, D.E., 1990, Geologic mapping, in Planetary mapping: Cambridge, GB, Cambridge University Press, p. 

208.

Wilson, L., 2001, Evidence for episodicity in the magma supply 

to the large Tharsis volcanoes: Journal of Geophysical 

Research, v. 106, no. E1, p. 1423–1434.
18

Table 1. Impact craters in V–1.

Crater

ID

Crater

Name

Latitude Longitude Diameter

(km)

Crater

Type1

Degradation2 Superposed

by

Superposing Central peak

present?

Infill material 

1 unnamed 80.9 226.4 2.9 Simple Degraded pdd - no Radar dark 

material

2 Tursunoy 80.9 229.3 4.5 Simple Degraded pbd - no Radar dark 

material

3 unnamed 

cluster

80 229.7 5.7, 7.5, 

5.0

Simple Degraded pdd/pdl - no Radar dark 

material

4 Eugenia 80.6 105.5 6 Simple Somewhat 

fresh

- pdd/wr no Radar dark 

material

5 Janice 87.3 262.4 11.9 Transition Somewhat 

degraded

- pbd/pdd/fb yes, small Radar dark 

material

6 Radka 75.6 96.3 13.1 Transition Somewhat 

degraded

lin pdd/pbs yes, small Not significantly infilled 

7 Gina 78.1 76.5 14.7 Transition Somewhat 

degraded

- fb/pds/pbs maybe Radar bright 

material

8 Tunde 76.8 792.9 ~15.0 Transition? Degraded lin pds/pdl no Radar dark 

material

9 Valborg 75.5 272.1 19.2 Complex Degraded - pbs yes Radar dark 

material

10 Ulrique 75.9 55.6 19.3 Complex Fresh - pdd yes Partly infilled 

with radar dark material

11 Fernandez 76.2 17.2 20.4 Complex? Somewhat 

fresh

- pds/pdl/ta no Radar dark 

material

12 Odilia 81.2 200.3 21.6 Complex Heavily 

degraded

rb/pbs/pds - no Partly infilled 

with radar bright material

13 Tatyana 85.4 214.6 21.8 Simple Somewhat 

degraded

rb/pds/wr - yes Radar bright 

material

14 Sveta 82.5 273.2 22.3 Simple? Fresh - pbs/pdd/pbs/lin yes, small Partly infilled 

with radar dark material

15 Efimova 81 223.3 26 Complex Fresh lin pdl/pbs yes Radar dark 

material

16 Hua Mulan 86.8 337.5 27.5 Complex Degraded pdd/psh1/lin - maybe Radar dark 

material

17 Rudneva 78.4 174.7 31.3 Complex Fresh - pds yes Radar dark 

material
19

Table 1. Impact craters in V–1—continued.

Crater

ID

Crater

Name

Latitude Longitude Diameter

(km)

Crater

Type1

Degradation2 Superposed

by

Superposing Central peak

present?

Infill material 

18 Landowska 84.6 76.9 ~37.6 Complex Degraded rb/pdd/pds - yes Radar bright 

material

19 Ruslanova 84 16.5 ~43.0 Complex Fresh - fb/pdl/pds yes Radar bright 

material

20 Volkova 75.2 242.2 46.9 Complex Fresh - pla/pdl/pbs yes Radar dark 

material superposed by radar bright material

21 Dashkova 78.2 306.5 52.3 Complex Heavily 

degraded

- an/pds/pbs/ta Yes Radar bright 

material

22 Lagerlof 81.2 285.1 59.8 Complex Degraded pdd/pds - Minor 

central peak cluster

Radar dark material

23 Klenova 78.2 104.7 143.5 Compound 

complex

Fresh - pds/pbs/wr Multi-ring 

basin

Radar dark material in interior, surrounded by multiple basin rings

1Crater types: simple craters are bowl-shaped, typically smaller diameter craters; transition craters have a small central peak; complex craters have 

prominent central peaks or central peak clusters; compound complex craters have concentric rings, largest diameter craters.

2Degradation of craters include 1) fresh craters, where ejecta deposits are observed to cover surrounding units and structures, 2) somewhat fresh 

craters, where the majority of the ejecta deposits overly surrounding units but might be partially embayed, 3) somewhat degraded craters, where ejecta deposits are visible but are deformed by surrounding structures, 4) degraded craters, where ejecta deposits are significantly embayed or modified by surrounding units and structures, and 5) heavily degraded, where ejecta deposits are completely embayed or crater rims are modified by surrounding structures.
20

Table 2. Area of units mapped in V–1.

Unit Label Percent Area*

Undifferentiated crater material c 1.7

Edifice unit ed 0.11

Lobate plains unit a, point source pla 3.6

Lobate plains unit b, linear source plb 0.3

Dark smooth corona plains material pcds 0.6

Bright smooth corona plains material pcbs 2.8

Fracture belt material fb 3.1

Bright smooth regional plains material pbs 7.2

Dark smooth regional plains material pds 23

Bright deformed corona plains material pcbd 0.85

Upper shield plains material psh2 0.04

Lower shield plains material psh1 4.0

Bright deformed regional plains material pbd 12

Dark deformed regional plains material pdd 14

Annulus unit an 1.5

Ridged belt unit rb 6.6

Densely lineated plains material pdl 14

Tessera unit a ta 4.4

Tessera unit b tb 0.2

*Total area in V–1: 6.6 x 106 km2
21

180°

270°

90°

270°

0°

75°

80°

85°

85°

80°

75°

180°

0°

75°

80°

85°

85°

80°

75°

A B

0 500 1000 KILOMETERS

Ridged beltsFracture beltsLobate plainsCraterTeserraCorona

Itzpapalotl Tessera Fulgora Dorsa Heloha Fluctus

SNEGUROCHKA

PLANITIA

LOUH

Laka Mons

Pomona

Corona

Anahit

Corona

Renpet

Mons

MaslenitsaCorona Lukelon

Dennitsa Dorsa

SarasvatiMons

fracture belt

lobate plains

Fortu

Figure 1. A, Magellan synthetic aperture radar (SAR) data for Snegurochka Planitia, V–1, Venus, from la

75° N. to 90° N.; B, Geologic sketch of the V–1 region with major tectonic and volcanic features labeled.
22

0 100 200 KILOMETERS

0 10 20 KILOMETERS

A

B

Figure 7. Regional plains near Klenova crater that have been extensively deformed by wrinkle ridges. 

A, This Magellan image, spanning from latitude 75° N. to 80° N. and from longitude 85° E. to 109° E., 

shows Klenova crater superposed on both radar dark plains and radar bright smooth plains units that are 

apparently associated with wrinkle ridges. Origin hypotheses for this radar bright material are discussed 

in the text. B, Detail of area in figure 7A. Evidence for local aeolian processes is seen in streaks on the 

edges of these radar bright deposits, but these streaks are not commonly seen in V–1.
23

0 20 40 KILOMETERS

0 40 80 KILOMETERS 0 20 40 KILOMETERS

A B 0 30 60 KILOMETERS 0 40 

D E

C

tatb

Figure 9. Examples of the heavily deformed units described in the text. A, 

Tessera unit ta clearly exhibits the two-directional deformation features that characterize tessera, while unit tb exhibits a slightly more subdued but still 

heavily folded deformation pattern. B, Densely lineated plains unit pdl exhibits 

the single direction of deformation, and the observed deposits generally have irregular boundaries with surrounding material. C, The ridged belt unit has a 

similar unidirectional deformation trend to the densely lineated plains unit, but 

material in this unit appears as ridges confined to 

entire region of V–1. D, In some cases, the direct

curved, leading to the formation of nearly conce

annulus unit an. The latter deposits are common 

coronae such as Anahit Corona shown in figure 9

with the fracture belt unit fb also appears confined appears to produce fractures and grabens rather th
24

B′

B

A′

A

C

A

A A′

B B′

C 

0 40 80 KILOMETERS B C 0 40 80 KILOMETERS 0 

0.80.60.40.2

–0.2

0

–0.4

–0.6

–0.8–1.0

Elevation (km)

0 50 100 150 200 300250 350

Distance (km)

Topographic Profile for Dennitsa Dorsa

0.80.60.40.2

0

–0.2–0.4–0.6

Elevation (km)

0 20 40 8060 100 120 160 180 140 200

Distance (km)

Topographic Profile for Lukelong Dorsa

1.61.41.21.00.80.60.40.2

0

Elevation (km)

0 20 40 

Topograp

Figure 10. Topographic profiles of three ridged belts observed in V–1, with the 

extent of each belt represented in bold on each profile. A, Dennitsa Dorsa 

appears to have troughs that parallel each side of the ridged belt. These troughs lie approximately 400 m–700 m below the adjacent plains while the ridged belt lies approximately 900 m above the plains. The plains appear to embay the 

ridged belt, at least partially covering the majority of the ridges that might splay 

into the surrounding areas. B, Lukelong Dorsa has a unique topographic profile, with the center of the belt forming a trough that lies 800 m below the 

surrounding plains. These relatively young dark 

been substantially deformed by wrinkle ridges tha

Dorsa, possibly indicating a continuing compres

perpendicular to the ridged belt. C, Fulgora 

boundary between Itzpapalotl Tessera and Snegutopographic signature, rising 600 m above the surplains materials in this area appear to have emb

evidence for significant deformation after emplac
25

A′

A

B′

B

C′

A 0 60 B C 0 100 200 KILOMETERS 0 

0

0.60.40.2

–0.2–0.2

0

–0.4

–0.6

–0.8–1.0

Elevation (km)

Distance (km)

Topographic Profile for Tezan Lineae

0.2

–0.2

0

–0.4–0.6–0.8

–1

–1.2–1.4–1.6

Elevation (km)

0 50 150100 200 300250 350

Distance (km)

Topographic Profile for Szel-anya Lineae

0.5

0

Elevation (km)

0 20 40 

Topographic P

Figure 11. Topographic profiles of three fracture belts observed in V–1, with the 

extent of each belt represented in bold on each profile. A, Tezan Lineae lies approximately 1 km below the adjacent plains units pdd, pbd, pds, and pbs (~1.4 km 

below MPR). These plains units appear to embay the belt of deformed material, and 

the relatively undeformed nature of the plains suggests that they are relatively 

young deposits. B, Szél-anya Lineae also is characterized by a trough that lies ~700 

m below the surrounding plains (~1.3 km below MPR), and the terrain on the 

opposite side of the fracture belt is elevated ~500–900 m above the surrounding 

plains (~100 m above MPR). This elevated terrai

terrain that is apparently cut by fractures associa

indicating that the fracture belt is the younger feanear the large shield volcano Laka Mons has a ra

200 m above the surrounding plains (400 m ab

plains unit pla in this area appear not only to have 

to be centered on the fracture belt, indicating th

formed as a result of the formation of the fracture 

120 KILOMETERS

0 20 40 8060 100 120 160 180 140 200

0.45

0.4

0.35

0.2

0.25

0.3

0.15

0.1

0.05

0

A A′

B B′

C 
26

0 20 40 KILOMETERS

0 40 20 KILOMETERS 0 20 40 KILOMETERS

0 30 60 KILOMETERS

A B

C D

Figure 12. Examples of regional plains units described in the text. A, Dark deformed plains unit pdd has 

small-scale deformation in the form of polygonal cracks or ridges deforming radar dark plains; B, bright 

deformed plains unit pbd generally has a rougher texture with a hummocky or deformed appearance; C, dark 

smooth plains unit pds is the darkest unit in mapped in the region and are generally characterized by a very 

smooth, undeformed morphology, though subsequent regional tectonism does superpose these deposits with 

wrinkle ridges and grabens; and D, bright smooth plains unit pbs is generally observed in association with 

either a topographic barrier or a fissure, and this unit typically covers surrounding material in deposits of a 

relatively undeformed radar bright texture.
27

0 30 60 KILOMETERS 0 40 80 KILOMETERS 0 10 20 KILOMETERS

A 0 20 40 KILOMETERS B C 0 20 40 KILOMETERS 0 20 40 KILOMETERS

D E F

Figure 13. Examples of localized plains units described in the 

text. A, Both shield plains units psh1 and psh2 are characterized by clusters of radar bright aprons that surround bright 

central peaks and, in some cases, overlap. In this case, the 

aprons of the shields in the lower shield plains unit psh1 appear 

to embay the nearby deformed material but are partially 

covered by the adjacent regional plains units, a stratigraphic 

sequence that is generally observed throughout Venus. B, 

Radar bright deformed and smooth corona plains units (pcbd, 

left white arrow and pcbs, right black arrow, respectively) have 

relatively high radar backscatter, and the deformed plains have 

small-scale deformation in the form of local wrinkles and 

cracks while the smooth plains generally lack significant 

tectonic deformation at the available data resolution. C, The 

radar dark smooth corona plains unit (pcds) has relatively low 

radar backscatter and is typically made up of undeformed 

materials that embay more heavily deformed materials in the 

interior of the corona plateau (for example, units pdl, an, ta). 

The more local distribution of units pcbd, pcbs, and pcds in 

association with coronae distinguish these materials from the 

morphologically similar regional plains units (fig. 12). D, and 

E, Lobate plains units pla (D) and plb (E) have distinctive 

patterns of material that ends in a digitate morphology with 

radar bright edges. Unit pla, shown in D, generally extends 

down slope from a central peak or source region such as the 

circular depression shown (Renpet Mons), and unit plb, shown 

in E, generally extends from lineaments likely associated with 

propagating dikes that feed local surface eruptions. F, Edifices 

(unit ed) have extremely high radar backscatter characteristic 

of layover caused by steep slopes, and some edifices are also 

associated with bright hummocky material that appears to 

originate from the flanks of the edifice itself.
28

D 0 40 80 KILOMETERS E F 0 40 80 KILOMETERS 0 

Figure 15. Examples of structures described in the text. A, Wrinkle ridges appear as radar bright ridge

that generally deform underlying regional plains units in the presence of compressive stresses. B, Simpl

ridges (black arrows) are distinct from wrinkle ridges in that they have broader ridge crests and ofte

cluster to form more heavily deformed geologic units. In contrast, lineaments (white arrows) appear arelatively straight features that cut across more tectonically deformed materials as well as regional plain

features, though some lineaments are embayed by other regional plains deposits. C, Steep-sided dome

also referred to as “pancake domes” (black arrows), are characterized by steep edges bounding a broad, fla

plateau, and they are commonly believed to form as the result of eruptions of viscous lavas.