Geologic Map of the Bereghinya Planitia Quadrangle (V–8), Venus 

By George E. McGill

Pamphlet to accompany

Geologic Investigations Series I–2794

2004

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration
BLANK
THE MAGELLAN MISSION

The Magellan spacecraft orbited Venus from August 

10, 1990, until it plunged into the Venusian atmosphere 

on October 12, 1994. Magellan had the objectives of (1) 

improving knowledge of the geologic processes, surface 

properties, and geologic history of Venus by analysis of 

surface radar characteristics, topography, and morphology and (2) improving 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 datasets: 

synthetic aperture radar (SAR) images of the surface, 

passive microwave thermal emission observations, and 

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 done in mission 

cycles 1, 2, and 3, from September 1990 until September 

1992. Ninety-eight percent of the surface was mapped 

with radar resolution of approximately 120 m. The SAR 

observations were projected to a 75-m nominal horizontal 

resolution; 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 

from about 20° to 45°.

High-resolution Doppler tracking of the spacecraft 

was done from September 1992 through October 1994 

(mission cycles 4, 5, 6). High-resolution gravity observations from about 950 orbits 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. Observations from 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 the morphology of the surface at a broad range of scales and 

by the intrinsic reflectivity, or dielectric constant, of 

the material. Topography at scales of several meters 

and larger can produce quasi-specular echoes, with the 

strength of the return 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 highdielectric minerals or coatings are thermodynamically 

stable. This effect 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. As such, 

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-meansquare (rms) slope. The topography data produced by this 

technique have horizontal footprint sizes of about 10 km 

near periapsis and a vertical resolution of approximately 

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 Bereghinya Planitia quadrangle (V–8) of Venus 

is bounded by 25° and 50° N. latitude, 0° and 30° E. longitude. It is one of 62 quadrangles covering the entire 

planet at a scale of 1:5,000,000. The quadrangle derives 

its name from the plains region Bereghinya Planitia, most 

of which falls within the boundaries of the quadrangle. 

Bereghinya are benevolent protective female spirits in 

East Slavic mythology. These spirits were considered as 

guardians of the home, and traditional homes commonly 

had carvings of Bereghinya around their windows. In 

addition, these spirits were associated with riverbanks, 

so some of them were envisioned as being women with 

fish tails, similar to mermaids.

The Bereghinya Planitia quadrangle comprises 

mostly plains materials that have been highly modified 

by younger structures, mostly related to coronae. The 

map area contains all or part of 22 named coronae, 4 

named deformation belts, and 2 major lava channel systems having extensive associated volcanic flows. In addition, other valles, a deformation belt, and coronae occur 

within the quadrangle but are unnamed. The quadrangle 

hosts 24 impact craters and 6 bright splotches believed 

due to explosive destruction of bolides in the atmosphere 

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(Campbell and others, 1992; Ivanov and others, 1992). 

Many of the impact craters have associated dark halos 

or parabolas, and four are accompanied by fields of secondary craters. Also present is a complex array of faults, 

fractures, and wrinkle ridges.

The quadrangle is geologically interesting primarily because of the large population of coronae, many of 

which are connected to each other by belts of closely 

spaced, complex wrinkle ridges producing a spiderlike 

pattern in which the “bodies” are coronae and the “legs” 

are the connecting belts. These coronae were named 

“arachnoids” by members of the Soviet Venera team 

(Barsukov and others, 1986). The problems of more than 

local interest include the kinematics and dynamics of 

the arachnoids, the structural and volcanic evolution of 

the coronae, and the age of the widespread background 

plains relative to structures and other material units.

METHODS AND DATA USED

Mapping was based on both hardcopy and digital 

versions of Magellan synthetic aperture radar (SAR) 

data. In cycle 1, the SAR incidence angles for images 

taken of the Bereghinya Planitia quadrangle ranged from 

33° to 44°. Mapping was carried out in Adobe Illustrator 

using a digital controlled mosaic of SAR images prepared 

by the U.S. Geological Survey. Individual tiles of 75 m/

pixel FMAPs were imported into Illustrator as needed 

to provide greater detail. Also helpful were 1:1,500,000 

photographic prints of 12° x 12° or 12° x 18° (depending 

on latitude) FMAPs, also provided by the U.S. Geological Survey. Topographic information was utilized in two 

ways: (1) as a color base layer in Illustrator that could 

be accessed simply by turning off the SAR base mosaic 

in the next higher layer, and (2) as pseudo-stereo versions of 225 m/pixel compressed-once mosaicked image 

data records (C1–MIDRs) created at the U.S. Geological 

Survey by using Magellan altimetry to generate artificial parallax on the SAR C1–MIDRs. The pseudo-stereo 

images were used to generate anaglyphs in Adobe Photoshop. For local detail, the original altimetry data were 

gridded in SURFER to prepare contour maps, topographic 

images, and three-dimensional mesh diagrams.

Stratigraphic material units were defined primarily 

by their relative radar brightness and surface textures, 

although crosscutting relations with structures, relative ages, and apparent association with topographic or 

structural features also were considered where appropriate and useful. Because the SAR images were all taken 

with intermediate to large incidence angles, the relative 

radar brightness of the various map units relates primarily to surface roughness at a scale comparable to the radar 

wavelength (12.6 cm). Characteristic values of important 

radar properties (radar backscatter coefficient, emissivity, 

reflectivity, and root-mean-square slope) were calculated 

for material units using programs provided by Campbell 

(1995). However, these properties were not used in the 

original unit definitions, which were based entirely on 

visual properties apparent in the SAR images. The radar 

parameters provide information about the nature (grain 

size, surface texture, dielectric constant) of the materials 

making up a map unit, and thus in some instances can 

contribute to determining the most likely origin of the 

unit.

STRATIGRAPHY

The stratigraphic units in the Bereghinya Planitia quadrangle are grouped into five broad categories 

according to terrain type: tessera, plains, coronae, miscellaneous flows and domes on plains, and impact craters. Twenty-seven units have been defined: one tessera 

unit, five plains units, seven flow units associated with 

coronae, nine miscellaneous flow and dome units, and 

five impact-crater units. Most unit names are based on 

characteristics visible on SAR images. Relative ages of 

units were determined primarily by embayment relations 

and truncation of structures at contacts; locally the relative ages of units not in contact with each other can be 

determined relative to a third unit or to structures. Quantitative radar properties for some units or types of units 

are summarized in table 1 and are compared (fig. 1) with 

the average scattering of the Venus surface as described 

by the Muhleman law (Muhleman, 1964).

TESSERA MATERIAL

Scattered within the Bereghinya Planitia quadrangle 

are radar-bright inliers within younger plains materials 

that are comparable to tessera terrain, as defined from 

Venera images (Basilevsky and others, 1986). All tessera 

material (unit t) has been intensely deformed into at least 

two sets of structures at high angles to each other. Some 

of these structures are grabens that are large enough for 

diagnostic criteria to be clearly visible on the Magellan 

images. Within most tessera inliers are small patches of 

radar-dark intratessera plains material. Many of these are 

actually continuous with the plains materials surrounding 

the tessera; those that are isolated from the surrounding 

plains are too small to map separately. The tessera inliers 

are heavily embayed by surrounding plains material, and 

the plains material floods the large grabens and abruptly 

truncates all other structures that crosscut the tessera 

material. All of the tessera inliers are in contact with, and 

older than, regional plains material (unit pr), and thus tessera material must be older than all materials younger 

than regional plains material. Bright plains material (unit 

pb), is in contact with tessera material at only one locality 

in the quadrangle (46 ̊ N., 0 ̊ E.). However, bright plains 

material is in contact with and younger than tessera material in the adjacent Sappho Patera quadrangle, where the 

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unit is called “lineated plains material” (McGill, 2000). 

In addition, bright plains material is consistently less 

deformed than tessera material. Although tessera material is almost certainly older than all other materials in the 

quadrangle, it is not possible to determine if it represents 

remnants of terrains that are fundamentally different and 

much older than regional plains material or if it is simply 

highly deformed plains material that is not significantly 

older than regional plains material. Furthermore, determining if the various patches of tessera contain materials of similar age is not possible; in fact, these materials 

could be of widely differing ages.

PLAINS MATERIALS

Most plains materials are characterized by low to 

intermediate brightness on the SAR images. Some of 

the geologic units mapped in the Bereghinya Planitia 

quadrangle are the same as those mapped in the adjacent 

Sappho Patera quadrangle (McGill, 2000), especially 

plains units, all of which were originally defined in the 

Sappho Patera quadrangle. Exposures of three plains 

units sit astride the boundary between the quadrangles, 

and thus these units are physically continuous from one 

quadrangle to the other. The three continuous units are 

regional plains, low-relief shield plains, and homogeneous plains materials.

Scattered about the quadrangle are numerous inliers 

of bright to extremely bright plains material (unit pb). 

All inliers of bright plains material are embayed by, and 

thus older than, the surrounding regional plains material. 

Bright plains material is generally deformed by one set 

of linear features (probably faults or fractures) that are 

truncated at contacts with surrounding plains materials. 

Locally, these linear features are closely spaced, forming 

a fabric that is penetrative at map scale. The large grabens 

that cut most areas underlain by tessera material are generally not present in inliers of bright plains material. The 

larger areas of bright plains material commonly occur on 

low rises that are surrounded by younger regional plains 

material. For many small bright patches on the plains, 

determining whether the brightness is due to the presence 

of bright plains material or to locally enhanced fracturing 

of the younger regional plains is difficult, suggesting that 

the bright plains material simply may be older, rougher, 

and generally more deformed plains material that otherwise is not fundamentally different from regional plains 

material.

Most of the Bereghinya Planitia quadrangle is underlain by regional plains material (unit pr). Regional plains 

material is by far the most widespread unit in the quadrangle, and it is characterized by a wide range of backscatter 

values that overlaps the backscatter values for most other 

units in the quadrangle (table 1, fig. 1). Regional plains 

material embays tessera and bright plains materials and 

is in turn embayed by flows derived from Gula Mons, by 

flows from many of the coronae in the quadrangle, by 

flows derived from valles, by flows associated with some 

shield fields, and by flows associated with domes. Scattered small volcanic edifices are common on regional 

plains material. Wrinkle ridges are nearly ubiquitous 

on regional plains but of widely varying abundance and 

brightness on SAR images. Because regional plains material is the dominant material unit mapped and because it 

is in contact with all other mapped materials, it is used as 

a local stratigraphic reference. This has been done fully 

recognizing that not all areas of regional plains need have 

formed at the same time; in fact, emplacement of this unit 

possibly occurred over an interval as long as 400 million 

years, which is a significant fraction of the mean surface 

age of the planet (for example, Hauck and others, 1998). 

However, the sparse crater population will not allow a 

credible estimate of the length of time involved. Nevertheless, defining time as pre-, syn-, and post-regional 

plains is useful and important because it provides a sense 

of crustal evolution in relative time.

Numerous large and small patches within regional 

plains material are characterized by an intricate array of 

bright lineations defining either a grid or a cellular pattern at a scale of one to several kilometers. In places, surrounding regional plains material appears superposed on 

this pattern, but more commonly the pattern simply loses 

sharpness so that contacts are gradational. These areas 

are indicated by a pattern overlay. The grid and cellular 

patterns of lineaments may be primary features of specific flows or portions of flows within the plains. At least 

some of the areas having a cellular pattern contain very 

closely spaced, small edifices, and thus the cellular pattern is probably due to fracturing around these edifices. 

Grid patterns present on otherwise typical plains material present a significant problem of scale because their 

dimensions are much greater than probable analogs on 

Earth (Johnson and Sandwell, 1992).

Completely enclosed within regional plains material 

are three areas mapped as low-relief shield plains material (unit psl). These areas appear superficially similar to 

the brighter areas included in regional plains material. 

However, low-relief shield plains are exposed on low 

rises having a relief of a few hundred meters. These rises 

are characterized by digitate and lobate flow lobes, and 

two of the three also have clearly visible source calderas. Low-relief shield plains material is superposed on 

regional plains material, but it formed before the development of all sets of wrinkle ridges present on the regional 

plains.

Dark plains material (unit pd) is present in a large 

area along the eastern boundary of the quadrangle. It 

occurs in a very shallow, irregular depression within 

regional plains. Dark plains material truncates lineations 

in adjacent regional plains material and ponds against 

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some of the wrinkle ridges superposed on regional plains 

material. Other wrinkle ridges cross the contact between 

dark plains and regional plains materials. Flows from two 

unnamed valles are superposed on dark plains material 

within the quadrangle. The low radar backscatter is due 

to a smooth surface (table 1).

Scattered about the quadrangle, most notably in the 

southeast corner, are areas having a bland, homogeneous 

texture and uniform, intermediate radar brightness. These 

areas are mapped as homogeneous plains material (unit 

ph). The contacts of homogeneous plains material are 

locally wispy, suggesting some modification by wind 

action. Homogeneous plains material truncates structures 

within bright plains material. Its age relative to regional 

plains material is less clear, but locally the contacts of 

homogeneous plains material appear affected by wrinkle ridges on regional plains material, implying that the 

homogeneous plains material is younger.

CORONA MATERIALS

Of the 29 coronae and coronalike structures in the 

Bereghinya Planitia quadrangle, 21 have mappable flows 

associated with them, and 1 additional structure, Ba’het 

Corona, has flows outside the quadrangle boundaries. 

Flows from four coronae (Onatah, units fcO1 and fcO2; 

Ponmakya, unit fcP; Kostroma, units fcK1 and fcK2; and 

Ilmatar, unit fcI)) are separately named because they 

yield useful relative-age information. All other corona 

flows are included within corona flows, undifferentiated 

(unit fcu). Most flows from coronae show digitate and 

lobate shapes to some degree, but some of these tend to 

lose distinctness in places so that defining the exact limit 

of a corona-derived flow field is commonly difficult. In 

general, the corona flows having high backscatter values 

are most obviously superposed on regional plains material. Corona flows that exhibit uncertain contacts with 

regional plains material have backscatter values that are 

very similar to backscatter values of regional plains material. The mapping has been conservative in this respect; 

that is, only where it is possible to trace the flow shapes 

from a corona out onto the surrounding plains have these 

flows been mapped as corona derived. Much of the material included within regional plains material probably is 

corona derived, but demonstrating this conclusively is 

not possible. Two coronae (Onatah and Kostroma) have 

sharply defined, radar bright digitate flows in addition 

to the less distinct shapes that generally characterize 

corona flow fields. Location, diameter, and key geologic 

relations for all coronae are summarized in table 3. All 

corona flows within the Bereghinya Planitia quadrangle 

appear to be superposed on regional plains material, or 

else are gradational with them, although the relative ages 

are locally difficult to determine. As will be discussed in 

the structural geology section, concentric and radial structures of coronae all cut regional plains material, although 

for some coronae these structures also cut an apparently 

older unit that is mapped as bright plains material. Generally, corona structures are also younger than corona 

flows. These observations imply that most corona flows 

are younger than or the same age as regional plains material and that the coronae as structures are dominantly 

post-regional plains material. Flows from valles are in 

contact with corona flows at only one locality; there, 

flows from Bayara Vallis are clearly superposed on flows 

from Sulis Corona. Very few data exist to relatively date 

the coronae. Flows from Yaroslavna Corona are superposed on a complex bundle of wrinkle ridges that in turn 

cuts flows from Cavell Corona, implying that Yaroslavna 

flows are younger than Cavell flows. Cavell flows cross 

the topographic rim of corona d, indicating that corona 

d is younger than Cavell Corona. Onatah Corona flows 

are superposed on flows from Audhumla Corona, and 

Onatah flows also truncate structures associated with 

Sigrun Fossae.

MISCELLANEOUS DOME AND

FLOW MATERIALS

Nine miscellaneous dome and flow units are mapped. 

These range from areally important units such as vallis 

flows and shield flows to features occurring at only one 

locality. All of these units are younger than regional 

plains material except some exposures of shield flows 

and possibly some domes.

Occurring as scattered exposures of varying sizes 

throughout the quadrangle are areas of shield flows (unit 

fs) that are related to clusters of small edifices, most of 

which are shield volcanoes. These clusters of edifices 

have been referred to as “shield fields” (Aubele and 

others, 1992). Not all small edifices occur in clusters, and 

not all clusters of edifices have an associated flow field, 

but the Bereghinya Planitia quadrangle contains a significant number of flow fields areally associated with shield 

fields. Shield flows have, on average, very similar radar 

backscatter to regional plains material. Wherever shield 

flows are in contact with corona flows and corona structures the shield flows are younger. An especially convincing example of this is found in the northwest corner 

of the quadrangle, where shield flows are superposed 

on structures related to Ba’het and Vasudhara Coronae. 

The quadrangle contains clear examples showing shield 

flows that are older than regional plains material, as well 

as clear examples showing shield flows that are younger 

than regional plains material. However, relative ages of 

shield flows and regional plains material are commonly 

ambiguous because both are transected by the same sets 

of wrinkle ridges. Thus individual areas of shield flows 

could be older, younger, or the same age as adjacent 

regional plains material.

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Scattered about the quadrangle are several volcanic 

domes and shields (unit d) ranging up to about 35 km 

in largest diameter. The age of these domes relative to 

regional plains material is generally not possible to determine directly. However, some domes have associated 

dome and shield flow material (unit fd) that is superposed 

on regional plains material, whereas others appear to be 

partially buried by regional plains material.

At several locations digitate or lobate flows superpose regional plains material. These flows have no 

obvious source, and they are characterized by a more 

homogenous texture and backscatter only slightly higher 

than adjacent regional plains material. These flows are 

mapped as flow material, undifferentiated (unit f). At one 

locality (14.5°–15° E., 34.5°–35° N.) very small, digitate 

flows have a vermiform texture at subkilometer scale and 

very high radar backscatter. These flows, mapped as textured flow material (unit ft), are superposed on regional 

plains material. The source for these flows is not apparent.

In the southwest corner of the quadrangle are long, 

narrow digitate flows derived from Gula Mons, which is 

southwest of the Bereghinya Planitia quadrangle. These 

flows have high backscatter, but one of them also has a 

radar-dark border, suggesting that the flow is rough in the 

center but smooth along the edges. Gula flow material 

(unit fG) is superposed on regional plains and also floods 

north-south grabens that cut regional plains. Ejecta from 

crater Browning is superposed on one of these flows.

In the northeastern part of the quadrangle are extensive flows derived from lava channels, two of which have 

been assigned names. These flows are generally digitate 

and have backscatter values ranging from much lower 

to much higher than the backscatter values of adjacent 

regional plains material. Three units are mapped: Bayara 

Vallis flow material (unit fBa), Belisama Vallis flow 

material (unit fBe), and unnamed vallis flow material 

(unit fv). These flow materials are among the youngest 

materials in the quadrangle, superposing regional plains 

material, dark plains material, and all corona flows and 

most corona structures they contact. They also are superposed on most structures but have been deformed locally 

by some structures related to Aušrā Dorsa and by sparse 

wrinkle ridges.

IMPACT CRATER MATERIALS

Deposits of 24 impact craters occur in the quadrangle. The craters range in diameter from 3.5 km (Elenora) 

to 81.7 km (Mona Lisa). Location, size, and general characteristics of these craters are summarized in table 2. Five 

impact-crater units are included on the map: crater material, undifferentiated (unit c), crater flow (outflow) material (unit cf), and crater floor materials, divided into three 

units on the basis of radar backscatter—dark crater floor 

material (unit cfd), intermediate crater floor material (unit 

cfi), and bright crater floor material (unit cfb). The three 

crater floor units represent differences in surface roughness of the floor materials; these have been distinguished 

in order to record any correlation between floor brightness and overall level of crater freshness (table 2). Seven 

craters have bright floors, which have radar backscatter 

values between –7.5 and –11.4 dB (mean = –9.7 dB); 

twelve craters have intermediate floors, which have radar 

backscatter values between –12.5 and –16.3 dB (mean = 

–13.9 dB); and four craters have dark floors, which have 

radar backscatter values between –17.5 and –21.1 dB 

(mean = –18.6 dB); Elenora is too small to resolve the 

floor separately. Four craters have associated secondary 

craters, and where these define a discrete field or chain 

they are delineated on the map by a dashed line and the 

letter “s.”

In addition to the 24 craters, the quadrangle includes 

6 splotches inferred to result from explosive destruction 

of bolides in the Venus atmosphere (Campbell and others, 

1992; Ivanov and others, 1992). These splotches occur 

as diffuse bright patches on the surface, generally with 

a vague circular pattern in the center. All six splotches 

occur in the southwestern part of the quadrangle.

All of the craters and splotches are younger than 

regional plains material. The only possible exception to 

this statement is the crater Mona Lisa, the largest and 

most degraded crater in the quadrangle. The arguments 

for an age younger than regional plains will be presented 

below, as will age relations of most craters with other 

units and structures. The craters will be discussed in latitude order, north to south.

Kauffman: The ejecta from Kauffman is somewhat 

asymmetrically distributed, which suggests a possible 

oblique impact from the northwest or west-northwest. 

The crater flow to the north of Kauffman ponds against 

narrow ridges that are part of Aušrā Dorsa.

Kemble: The asymmetry of ejecta from Kemble suggests an oblique impact from the west. Crater flows are 

restricted to the eastern downrange side of the crater. 

These flows flood northeast-trending grabens that are 

part of Sigrun Fossae. On the west, Sigrun Fossae structures cut the rim and ejecta of Kemble.

Elenora: This small, irregular crater is superposed 

on flows from Onatah Corona, which are among the 

youngest materials in the quadrangle. For a small crater, 

Elenora has a surprisingly large and complete dark halo.

Chubado: Chubado is a small, irregular crater that 

occurs on the broad ridge that connects Audhumla and 

Ba’het Coronae. This ridge is characterized by a complex 

array of bright lineaments; those trending northwest, parallel to the trend of the ridge, are superposed by Chubado 

ejecta, whereas those trending slightly west of north, 

and thus that transect the ridge obliquely, cut Chubado 

ejecta.

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Prichard: Ejecta from Prichard are symmetrical 

about the crater. Although crater flows at Prichard are 

not apparent, some diffuse deposits having backscatter 

slightly above that for the local regional plains could 

be crater flows rather than simply representing normal 

variability of regional plains backscatter. Prichard ejecta 

is superposed on wrinkle ridges making up the belt that 

connects Audhumla Corona to Kostroma Coronae.

Ariadne: Ariadne is astride the boundary between 

the Bereghinya Planitia and Sedna Planitia quadrangles. 

Its ejecta is symmetrical around the crater. A few secondary craters are present within the Bereghinya Planitia 

quadrangle. A long crater flow extending southward from 

Ariadne may be cut by east-west-trending wrinkle ridges, 

although the evidence is somewhat ambiguous.

Ruth: Ruth has nearly symmetrical ejecta that yields 

ambiguous age relations with wrinkle ridges on the surrounding regional plains.

Talvikki: Talvikki ejecta distribution is nearly symmetrical. Wrinkle ridges on surrounding regional plains 

appear to cut Talvikki ejecta.

Lena: The ejecta from Lena is slightly asymmetrical, which suggests a possible oblique impact from the 

south-southwest. The crater is superposed on the belt of 

wrinkle ridges that extends southeastward from Yaroslavna Corona.

Stina: Stina ejecta approaches a butterfly pattern, 

which indicates oblique impact from the east-southeast. 

Northwest-trending wrinkle ridges cut crater flows from 

Stina.

Esterica: This small doublet crater provides no 

useful stratigraphic information.

Wilma: Ejecta from Wilma is somewhat asymmetrical, which suggests oblique impact from the southwest. 

Most crater flows are on the northeast side of the crater.

Ayisatu: The ejecta from Ayisatu forms a highly 

asymmetric butterfly pattern, which indicates oblique 

impact from the north-northwest. The ejecta is superposed on north-south-trending wrinkle ridges.

Melanka: Melanka is a doublet crater having highly 

asymmetric ejecta, which indicates oblique impact from 

the northeast. Crater flows occur to the west and southwest. Ejecta appears to be superposed on north-southtrending grabens.

Noreen: Ejecta from Noreen is approximately 

symmetrical about the crater. Noreen is superposed on 

structures in the belt that links corona f, Bécuma Mons, 

Dzuzdi Corona, and Cavell Corona. Noreen is the apparent source of a band of alternating light and dark streaks 

that extends for about 900 km westward from the crater.

Edgeworth: Except for a small gap in the ejecta 

blanket northeast of Edgeworth, the ejecta from Edgeworth is approximately symmetrical. Edgeworth ejecta 

is superposed on northwest-trending wrinkle ridges. The 

crater lies within the horseshoe-shaped ridge that defines 

the highly irregular corona f. Edgeworth is the apparent 

cause of a large, radar-dark parabola that overlaps with 

the streaks from Noreen. The parabola is an area of relatively low emissivity (fig. 2).

Defa: The crater rim appears incomplete to the 

southwest, and most ejecta and flow materials occur to 

the northeast, both suggesting oblique impact from the 

southwest. Crater flows flood north-northeast-trending 

grabens. Defa is superposed on flows from Ponmakya 

Corona.

Mukhina: Except for a small gap in the south-southwest, the ejecta from Mukhina is approximately symmetrical. Secondary craters occur mostly to the north, which, 

with the ejecta gap, suggests a possible oblique impact 

from the south-southwest.

Halima: Halima ejecta forms a distinctive butterfly 

pattern, which indicates oblique impact from the southsoutheast. Ejecta appears to be both superposed on and 

cut by north-south-trending grabens.

Browning: Ejecta from Browning approaches a butterfly pattern, which indicates oblique impact from the 

southwest. Secondary craters are abundant on all sides of 

the crater except to the southwest. The crater appears to 

be superposed on wrinkle ridges present on the surrounding regional plains. It also is superposed on one of the 

flows from Gula Mons.

Kafutchi: This doublet crater has one member that 

is more than twice the size of the other. Kafutchi occurs 

within Beyla Corona, and north-south lineations characteristic of the interior of Beyla cut the crater.

Bachira: Bachira ejecta is approximately symmetrical. Relations with wrinkle ridges are ambiguous.

Ferber: Ferber ejecta is approximately symmetrical. 

Secondary craters occur around the entire crater except 

to the southeast. To the west are both a dark parabola 

and bright/dark streaks that extend for more than 300 km 

away from the crater.

Mona Lisa: Mona Lisa is a double-ring structure 

having ring diameters differing by about a factor of 

two. The interior of the structure consists of dark floor 

material that superficially resembles the regional plains 

that occur external to the crater. To the east, the plains 

material is homogeneous plains, and whether a contact 

exists between homogeneous plains material and crater 

flows within this relatively bright area is not clear. To 

the south, a contact is mapped between crater flows and 

homogeneous plains material, but which is younger is not 

known. However, along the west and northwest sides of 

Mona Lisa the relations seem to be clear—the ejecta is 

superposed on regional plains material. Wrinkle ridges 

cut Mona Lisa crater flows to the south and northwest. 

Finally, the dark material on the floor of Mona Lisa is 

characterized by a “cellular” pattern of wrinkle ridges, 

which is geometrically different from the more rectilinear sets of wrinkle ridges on the regional plains.

6
STRUCTURAL GEOLOGY

INTRODUCTION

The Bereghinya Planitia quadrangle includes a very 

complex array of structural assemblages and individual 

structural elements. Assemblages include deformation belts of various types, graben swarms, fabrics of 

narrow, radar-bright lineaments, and structures associated with coronae. Individual structural elements include 

radar-bright lineaments, grabens, wrinkle ridges, ridges 

of deformation belts, and broad, low ridges. Some of 

these individual structural elements can be conveniently 

described as part of the discussion of structural assemblages; others require separate treatment. The structural 

assemblages are considered first.

DEFORMATION BELTS

The quadrangle includes all or parts of five deformation belts: Sigrun Fossae, Aušrā Dorsa, Hera Dorsa, 

Tomem Dorsa, and a small, unnamed belt centered 

at about 46.5° N., 26° E. Sigrun Fossae is a complex 

northeast-trending belt of lineaments and grabens that 

is mostly within the Fortuna Tessera quadrangle to the 

north. Where the belt enters the Bereghinya Planitia quadrangle between 15° and 20° E. it is about 250 km wide 

and includes both closely spaced belt-parallel grabens 

and a penetrative fabric of north-south-trending to northnorthwest-trending lineaments. The belt fans southward 

and ends at about 47° N., where it merges with structures 

associated with Audhumla Corona. The fanning results 

in some belt-parallel grabens on the west side of the belt 

curving toward an east-west trend and some on the east 

side of the belt curving toward a north-south trend. The 

topography in the general area of Sigrun Fossae (fig. 3) 

does not relate to the structural elements or trends of the 

belt, and thus no belt-scale topography is associated with 

Sigrun Fossae. Faults and lineaments of Sigrun Fossae 

cut bright plains material and, locally, regional plains 

material but are truncated by flows from Onatah Corona 

and Bayara Vallis. Sigrun structures are both older and 

younger than crater Kemble, demonstrating that deformation has been progressive.

Aušrā Dorsa is a northeast-trending composite belt 

that is about 75 km wide where it enters the quadrangle 

at 27° E. Immediately to the north, in the Fortuna Tessera quadrangle, it merges with a larger belt that trends 

north-south. A narrow moat extends along both sides of 

Aušrā Dorsa for almost its entire length so that it is generally elevated above the immediate surroundings (fig. 

3). Aušrā Dorsa widens and the individual structural 

elements become more widely spaced southward, and it 

cannot be followed as a discrete structural feature south 

of about 44° N. The belt includes belt-parallel ridges of 

two scales, and transverse northwest- to east-west-trending lineaments. Some of the ridges appear to be typical 

wrinkle ridges having widths less than 1 km; others are 

broader, gentler features that are up to about 8.5 km wide. 

The latter are inferred to be gentle ridges because of the 

gradual change from radar-bright to radar-dark across 

them, but the widest of these also show relief on the anaglyph at C1–MIDR scale. Both the wrinkle ridges and the 

broader ridges are consistent with contraction normal to 

the length of the belt. The transverse lineaments are generally too narrow to permit resolving their geometry, but 

some are wide enough to suggest that they are grabens. 

Thus these structures are assumed to be of extensional 

origin. The lineaments of Aušrā Dorsa deform regional 

plains material, but age relations for the ridges are ambiguous. Flows from Belisama Vallis are diverted by Aušrā

Dorsa, but the transverse extensional lineaments cut both 

the belt and the vallis flows.

The small deformation belt centered at about 46.5° 

N., 26° E. is 150 km long and 25 km wide at its widest 

point. The material of the belt is mapped as bright plains 

(unit pb). No overall topography is associated with the 

belt. Within it, however, are gentle ridges of the type 

found within Aušrā Dorsa that are up to about 3 km wide. 

Flows from Edda Corona pond against one of these gentle 

ridges, and the entire belt appears embayed by regional 

plains material.

Tomem Dorsa consists of a north-south-trending 

bundle of closely spaced wrinkle ridges in the southwestern part of the quadrangle. Tomem Dorsa differs from the 

belts of wrinkle ridges that connect many of the coronae 

in Bereghinya Planitia only because it is not related to 

coronae. Hera Dorsa is defined by very subtle, northwesttrending ridges of regional plains material separated by 

equally subtle northwest-trending troughs occupied by 

dark plains material.

Many of the coronae in the Bereghinya Planitia quadrangle are connected by belts of closely spaced structures 

that commonly reside on broad, subtle ridges, many of 

which show clearly even on a small-scale topographic 

map (fig. 3). Because some coronae are connected to 

others in more than one direction, the overall pattern 

reminds one of a spider, hence the name arachnoids (Barsukov and others, 1986), a term that should be avoided 

because it masks the basic similarity of the features in 

this quadrangle to coronae elsewhere on Venus (Stofan 

and others, 1992, 1997). However, the nature of the structures occurring on the “spider legs” is of some importance. Many of the individual structural elements within 

the belts are too narrow to resolve their geometry. Most 

of these are sinuous and thus are inferred to be wrinkle 

ridges similar to those found on the plains over most of 

the planet. However, they are much more closely spaced 

than is generally the case. The most interesting structures 

in the belts are sinuous, ropy lineaments that commonly 

include two bright strands, each about the same width 

7
as a typical wrinkle ridge, that are either parallel to each 

other or intricately braided. Locally, these braided pairs 

appear to lie on a very subtle ridge that is the width of the 

braided pair or wider.

CORONAE

The Bereghinya Planitia quadrangle contains an 

unusually large assemblage of coronae and coronalike 

features. These range in size from Kumang Corona, 

which has a diameter of 41 km, to Beyla, which has a 

long diameter of 326 km and a short diameter of 236 

km. In all, the quadrangle contains 29 coronae, of which 

5 (Ba’het, Cavell, Sand, Trotula, and Yaroslavna) were 

originally designated as paterae. In addition, seven coronae and coronalike features are unnamed; these are designated on the map by lower-case letters, a–g (from north 

to south). Location, size, and key characteristics of each 

feature are presented in table 3.

As discussed above, complex belts of wrinkle ridges 

link many of the coronae, thus forming clusters and 

chains of coronae. One of the corona chains is continuous 

with the deformation belt Aušrā Dorsa. The coronae in 

the Bereghinya Planitia quadrangle exhibit a wide range 

of structural and topographic characteristics. Most are 

defined by both concentric topographic rims and fracture 

rings, although the two do not coincide for some coronae. 

Topographic rims are actually ridges that are elevated 

above the surrounding plains as well as above the centers 

of coronae. Fracture rings consist mostly of radar-bright 

lineaments that are too narrow to resolve their geometry, 

but also included are well-defined grabens. Commonly, 

the bounding rims and rings do not completely encircle 

the structure. Most of the coronae are depressed in their 

centers (fig. 3), but some show no obvious topography 

(for example, Onatah and a) and one (e) has a central 

mound rather than a depression. Some central depressions 

are simple (fig. 4), others include more complex interior 

topography (fig. 5). Most of the coronae are sources of at 

least some flows, but a few have no associated volcanic 

material. Generally, flows from different coronae are not 

in contact with each other, a situation that complicates 

determining relative ages. The sizes of coronae are difficult to define in most instances, in part because of the 

incompleteness of many topographic rims and fracture 

rings, in part because of the irregular shapes of many of 

these features. Fracture rings and topographic rims have 

finite widths; diameters quoted in the table were measured from the centers of the fracture bands defining the 

coronae rather than from the inner or outer edge of these 

bands and from ridge crest to ridge crest of topographic 

rims. Concentric or radial structures associated with all 

of these coronae, except possibly Ba’het Corona, deform 

regional plains material (unit pr). Some also deform 

bright plains material. The coronae are described below 

in order from north to south across the quadrangle.

Onatah Corona: Onatah is a large feature characterized by very poorly developed concentric structure, no 

distinctive topography, and very extensive flows, some 

of which extend north of the quadrangle boundary. The 

main source for flows is on the eastern and southeastern 

rim of the structure, and flows from this source fill the 

central region of the corona and cover a large area mostly 

to the east, south, and north. No flow sources are apparent 

in the central region of the corona. Flows to the east and 

south are largely confined north of an older low, arcuate ridge that joins Sigrun Fossae and Audhumla Corona 

to Ba’het Corona. Onatah flows have a lower density 

of wrinkle ridges than plains materials and flows from 

other coronae. Radial and concentric fractures occur only 

along the western side of the corona. These fractures cut 

Onatah flows. The radial fractures link Onatah Corona to 

Ba’het Corona.

Damona Corona: This corona is a complex, kidneyshaped structure having limited flows, most of which are 

in the interior of the corona. Damona is bounded by an 

incomplete ring of concentric fractures and a partial topographic rim on the northwest side only. Corona fractures 

do not appear to cut the flows derived from the corona.

Ba’het Corona: Ba’het is an irregular, elongate 

corona, most of which is west of the Bereghinya Planitia 

quadrangle. The corona is almost completely bounded by 

a fracture ring but has a topographic rim only along the 

north side. The interior contains a large patch of radar 

bright, densely lineated bright plains material (unit pb), 

which suggests that Ba’het is older than regional plains 

material or that the bright plains material survived the 

process that formed the corona. No flows from Ba’het are 

apparent within the Bereghinya Planitia quadrangle, but 

flows derived from Ba’het occur west of the structure. 

These flows are cut by both radial and concentric Ba’het 

fractures. The interior of the corona is flooded with 

younger shield flows and flows from Onatah Corona.

Edda Corona: Edda Corona lies at the north end of 

the small, north-northwest-trending ridge belt discussed 

above that consists of bright plains material (unit pb). 

About half of its circumference is defined by a topographic rim and a fracture ring that are coincident. Flows 

are moderately extensive, and these appear to pond 

against ridges in the ridge belt and also against northeasttrending wrinkle ridges that deform regional plains material, but they are cut by concentric corona fractures.

Audhumla Corona: This corona has an intensely fractured northern border but essentially no fractures defining its southern border. No topographic rim is evident. 

The intensely fractured material of the northern border 

is mapped as bright plains material (unit pb). Separating 

Audhumla structures from structures in Sigrun Fossae 

is very difficult because fossae structures intersect and 

merge with the fractures that form the northern border 

8
of the corona. The relation is one of mutual crosscutting, and thus whether Audhumla is older than, younger 

than, or the same age as Sigrun Fossae is not possible to 

determine. Flows are not extensive, but because they are 

superposed by flows from Onatah Corona they are probably more widespread beneath the younger unit. Structures related either to Audhumla or to Sigrun Fossae cut 

Audhumla flows.

Corona a: This corona is a poorly defined structure 

having no topographic rim and an incomplete, narrow 

fracture ring. Corona a lies partly within Aušrā Dorsa, 

and its eastern half is deformed by ridges and lineaments 

that are part of the dorsa. No apparent flows derive from 

this corona.

Parma Corona: Parma Corona is bounded by a topographic rim and a fracture ring, both of which extend 

about half way around the structure. The relations of 

corona structures with flows from Bayara Vallis are 

mixed; to the south, Bayara flows are clearly superposed 

on corona structures, including fractures of the concentric 

ring. To the north, however, some more distal concentric 

structures related to Parma cut Bayara flows. Thus the 

corona structures and the vallis flows overlap in time. 

Derived flows are limited to the corona interior; they do 

not appear to be cut by any corona structures.

Sulis Corona: Sulis Corona is an almost perfect 

doughnut shape; its outer edge is delineated by a narrow 

but complete fracture ring, inside of which is a complete 

topographic rim. The elevated rim is characterized by 

approximately evenly spaced, radiating wrinkle ridges. 

Flows occur only to the east of the corona, where they 

are moderately abundant. Concentric corona structures 

cut these flows, as do the ridges in the belt connecting 

Sulis with Parma Corona. Flows from Bayara Vallis are 

superposed on Sulis flows.

Vasudhara Corona: A wide concentric fracture ring 

bounds Vasudhara Corona for about half of its circumference, but the corona lacks a topographic rim that is higher 

than surrounding terrain. Flows occur mostly west and 

southwest of the corona. These flows are cut by concentric corona fractures. An extensive shield flow is superposed on Vasudhara flows and also sharply truncates both 

concentric and radial fractures related to the corona.

Corona b: No flows are associated with corona b, and 

the bounding fracture ring is narrow, incomplete, and not 

altogether convincing. However, a complete topographic 

rim surrounds the depressed center, forming a doughnut shape similar to that of Sulis Corona. Thus corona 

b qualifies as a stealth corona (Tapper, 1997; Stofan and 

others, 2001). This topographic rim appears to consist of 

regional plains material. Distal structures of Aušrā Dorsa 

cut corona b.

Corona c: This feature is an irregular, elongate 

structure having a depressed center but only a partial 

and poorly developed bounding fracture ring and no 

topographic rim. Flows are moderately extensive. Structures apparently related to the corona cut these flows, 

but because corona c lies within a more extensive belt of 

ridges and fractures structures actually associated with 

the corona are not apparent. This structure is best categorized as “coronalike” because the structures and topography generally considered diagnostic of a corona are not 

well developed.

Sand Corona: Sand Corona is similar to Sulis Corona 

in being bounded by a narrow fracture ring that, unlike 

the ring for Sulis, is not complete. Inside this narrow 

ring is a complete topographic rim having approximately 

evenly spaced, radiating wrinkle ridges. This rim consists 

of elevated regional plains material. The central depression of Sand Corona is very irregular (fig. 5) rather than 

being nearly circular as is the central depression of Sulis 

Corona. Sand Corona lies in a well-developed belt of 

complex wrinkle ridges that connects Trotula and Sand 

Coronae to the northwestern twin of Nana-Buluku Coronae. Flows are not extensive and are mapped only east 

of the corona. These flows are cut by the wrinkle ridges 

connecting Sand and Trotula Coronae.

Trotula Corona: Trotula Corona has an interesting 

shape. The broad, nearly complete fracture ring defines 

a teardrop shape, whereas the smaller, complete topographic rim, which lies inside of the fracture ring, is 

circular. The topographic rim is characterized by approximately evenly spaced radiating wrinkle ridges, similar 

to what is present at Sulis and Sand Coronae. Flows are 

sparse and limited to the depressed center of the structure. 

Corona structures do not cut these flows, but the flows do 

not appear to be superposed on any structures either.

Simoting Corona: Simoting is a true stealth corona; it 

is defined entirely by a topographic rim and has a belt of 

fractures only along about half of its west side. Despite its 

large size, this structure was not discovered by those who 

named the nearby features of comparable or somewhat 

smaller dimensions. The topographic rim is characterized 

by approximately evenly spaced radiating wrinkle ridges, 

like those present at Sulis, Sand, and Trotula Coronae. In 

stereo, this structure looks like a rubber life raft! The topographic rim appears to consist of regional plains material. Simoting Corona possibly should be considered part 

of Trotula Corona, which then would become a twin or 

multiple structure. It is named and described separately 

because it is structurally unlike Trotula.

Kostroma Coronae: These structures form twin or 

multiple coronae, consisting of two connected parts, the 

total being elongate in a west-northwest direction. The 

southeast twin is almost completely surrounded by a 

broad fracture ring; the northwest twin is bounded by a 

narrow and incomplete fracture ring but also by a complete topographic rim (fig. 6). Flows are extensive, and 

the older ones are cut by concentric corona fractures. The 

terrain northeast of the coronae is relatively low, and at 

9
least the youngest lavas from Kostroma Coronae have 

flowed down the slope into this low area, superposing on 

regional plains material.

Nana-Buluku Coronae: Nana-Buluku Coronae are 

twin or multiple coronae similar in appearance, orientation, and size to Kostroma Coronae. Both twins have 

fracture rings and topographic rims. For the northwest 

twin, the fracture ring lies inside the topographic rim; for 

the southeast twin, the two boundaries coincide. Flows 

are limited in extent and appear to be cut by concentric 

corona structures.

Yaroslavna Corona: This corona is an irregular structure having two concentric topographic rims. The outer 

rim is narrow and coincides with the incomplete fracture 

ring; the inner rim is broader and immediately surrounds 

the central depression. Three flows, each having a different morphology, emanate from Yaroslavna. To the west is 

a digitate flow with morphology typical of most flows on 

Venus; to the north is a stubby lobe-shaped flow with a 

hummocky surface; and to the southeast is a stubby lobeshaped flow with a smooth surface. These stubby flows 

may consist of lavas more evolved than the basalt inferred 

to make up most flows on Venus. Concentric Yaroslavna 

structures cut all three of these flows, but the lobe-shaped 

flows appear younger than many structures on the surrounding plains and younger than the digitate flow.

Corona d: Corona d lies close to and north of Cavell 

Corona but was not recognized by those who named adjacent structures because it is essentially a stealth structure. 

It is defined primarily by a horseshoe-shaped topographic 

rim that is open to the south, toward Cavell. Flows from 

Cavell Corona are apparently continuous across the topographic rim of corona d, which suggests that this corona 

is younger than the volcanism associated with Cavell 

Corona. Where not surfaced by flows from Cavell, the 

topographic rim of corona d consists of elevated regional 

plains material.

Cavell Corona: Cavell Corona is a well-defined 

structure having a wide and complete fracture ring coincident with a complete topographic rim, and a deep central depression. Flows are extensive and, as discussed 

above, appear to be older than the topographic rim of 

corona d. Concentric and radial structures from Cavell 

cut Cavell flows.

Xquiq Corona: Concentric ring fractures wrap around 

the west, south, and east sides of this corona and then 

taper northward toward Nana-Buluku Coronae to form 

an overall teardrop pattern. Where the fracture ring tapers 

northward the northern boundary of Xquiq is defined by 

a short segment of topographic rim, such that the central depression is a more normal oval shape. Flows are 

extremely limited and are cut by the ring fractures.

Corona e: Corona e has no topographic rim and a 

very narrow and poorly developed fracture ring. The only 

significant topography associated with the structure is a 

central mound, rather than a central depression. No flows 

associated with this corona have been identified.

Dzuzdi Corona: The central part of Dzuzdi is a wellformed doughnut shape, with a complete topographic 

rim circling the central depression. External to the topographic rim is a broad but incomplete fracture ring that 

circles about half of the corona. Dzuzdi Corona is in a belt 

of complex wrinkle ridges that links corona f, Bécuma 

Mons, Dzuzdi Corona, and Cavell Corona. Structures in 

this belt deform corona Dzuzdi. No associated flows have 

been found.

Ilmatar Corona: Ilmatar Corona is bounded by 

a broad, complete fracture ring that coincides with a 

nearly complete topographic rim. Flows are limited. To 

the south a small area of Ilmatar Corona flow material 

(unit fcI) is cut by a corona concentric structure; to the 

north is a stubby lobate flow that is superposed on fractures of the corona ring. The stubby flow may consist of 

a more evolved magma, similar to those associated with 

Yaroslavna Corona. The floor of the corona hosts a dense 

array of wrinkle ridges that have an orientation not quite 

parallel to the wrinkle ridges external to the corona.

Ponmakya Corona: Ponmakya Corona has a ring of 

fractures only around its northern part where a partial 

topographic rim also may be present. The center of the 

corona is completely flooded with volcanic material, and 

the southern boundary of the structure is inferred to be 

near the northern limit of a strong array of radial fractures 

that is present south of the flooded interior of the corona. 

Flows from this corona also cover extensive areas north 

and south of its flooded interior. Shield flows are superposed on radial structures of Ponmakya.

Modron Corona: Modron Corona is a small and 

almost perfectly circular structure defined by a broad and 

nearly complete fracture ring that is coincident with a 

nearly complete topographic rim. The only gap is a small 

one to the north through which younger shield flows have 

penetrated the interior of the corona, superposing ring 

fractures. A small flow field east of the structure is probably derived from this corona.

Corona f: Corona f is an unusual structure that is 

primarily bounded by a low, discontinuous topographic 

rim that defines a large horseshoe pattern, open to the 

north. This ridge extends all the way north to Bécuma 

Mons, and it crosses Modron Corona as well. The crater 

Edgeworth is entirely within the structure. South of the 

topographic rim is a smaller horseshoe pattern defined 

by fractures. Thus this structure may be a twin corona or 

coronalike feature. Flows are not very extensive, and at 

least some are cut by corona structures.

Corona g: This corona is a very subtle feature having 

a poorly developed fracture ring and no topographic rim. 

The interior topography is complex with both elevated 

and depressed regions, none of which exhibit much relief. 

Flows are moderately abundant. Corona g structures cut 

10
its flows. This feature is probably best categorized as a 

coronalike structure.

Beyla Corona: The largest corona in the quadrangle, 

Beyla has an associated fracture pattern that reminds one 

of a trilobite. An outer fracture ring defines the structure. 

This ring is broad and very well developed in the northern part of the corona, much narrower and less obvious 

to the south. In the northern part of the corona a second 

broad fracture ring lies within the main ring. Also in the 

northern part of the corona a partial topographic rim is 

present just inside the outer fracture ring. The central 

depression appears to be deeper in the north than in the 

south, and a large elevated area occurs in the center (see 

Squyres and others, 1992a, fig. 11b). Coincident with the 

central elevation is a strong fabric of north-south fractures that have the same trend but are not continuous with 

radial structures extending northward from the corona. 

Flows are limited, and those that are present are cut by 

concentric corona structures. Some corona fractures also 

cut crater Kafutchi, which is on the central elevated area 

within the corona.

Kumang Corona: Kumang Corona is the smallest 

corona in the quadrangle. It is bounded on both east and 

west sides by partial fracture rings and coincident topographic rims. The interior is flooded by flows from the 

corona. This corona is the focus of spectacular fans of 

grabens both north and south of the corona. These grabens cut regional plains, but they cut only the periphery 

of the corona flows in the central part of the structure. 

However, structures of the incomplete fracture ring cut 

these corona flows.

TESSERA STRUCTURES

Structures deforming tessera material are of three 

general types: grabens, broad ridges, and narrow, bright 

lineaments of uncertain genesis. Grabens cutting tessera 

material are common and can range in width from the 

limit of recognition resolution (a few hundred meters) 

to as much as 10 km. Grabens in any given exposure of 

tessera have one or at most two orientations, but tessera 

graben trends over the entire quadrangle exhibit no consistent pattern. Many grabens are flooded by surrounding 

plains or other volcanic materials. The bright lineaments 

are spaced from less than 1 to 2 or 3 km apart and, like the 

grabens, are generally confined to one or two orientations 

within any single tessera exposure but are not characterized by common trends quadrangle-wide. Commonly 

these lineaments are so closely spaced that they represent 

a penetrative fabric at SAR resolution. This fabric effectively masks the original characteristics of tessera material and causes the backscatter and root-mean-square 

(rms) slope to be very high (table 1). Ridges are relatively 

rare and when present commonly trend about parallel to 

the narrow bright lineaments. All of these structures are 

sharply truncated at contacts between tessera and surrounding units.

FRACTURES, FAULTS, AND LINEAMENTS

As was true for the Sappho Patera quadrangle 

(McGill, 2000), plains materials in the Bereghinya Planitia quadrangle are cut by a fabric of narrow radar-bright 

lineaments that have no obvious association with any 

other structural or topographic feature. Individual lineaments range in length from a few to more than 100 

km. Over much of the quadrangle, this fabric cannot be 

separated from the complex lineament patterns associated with coronae and deformation belts. However, in the 

southern part, where these complexities are not present, 

the lineaments define a fabric trending between northsouth and north-northeast. The lineaments are inferred 

to be extensional fractures based on local evidence of 

graben geometry for some of them. Locally relative ages 

of structures deforming plains materials can be determined; this fabric appears to be consistently older than 

both radial graben sets and wrinkle ridges.

Four features within the Bereghinya Planitia quadrangle are included in a global catalog of graben swarms that 

could be due to the presence of radially propagated dikes 

that did not reach the surface (Grosfils and Head, 1994; 

E.B. Grosfils, written commun., 2001). The four sources 

listed are Ba’het Corona, Audhumla Corona, Ponmakya 

Corona, and Bécuma Mons. The most pronounced radial 

structures associated with Ba’het Corona are those in the 

structural bundle connecting Ba’het and Onatah Coronae. 

These could, of course, overlie buried dikes, but the pattern is not really radial in the sense that the individual 

structural elements do not diverge from each other with 

distance from the presumed source. Audhumla Corona 

does not have a well-defined radial pattern at all. Most 

clearly associated lineaments and grabens are concentric 

rather than radial, and those that are more nearly radial 

probably relate more to Sigrun Fossae than they do to 

Audhumla Corona. Bécuma Mons is the center for a spectacular set of radial grabens, which could be due to radial 

dikes. Ponmakya Corona also has well-defined grabens 

radiating from its center, most of which occur to the north 

and south. Two other possible centers of radiating dikes in 

the quadrangle are much smaller than the four proposed 

by Grosfils and thus easily missed in a global search using 

lower resolution images. The first of these is the area of 

low-relief shield plains material (unit psl) centered just 

south of the southern border of the quadrangle at about 6° 

E.; the other is Kumang Corona, centered at 25° N., 11.8° 

E. Individual grabens in these two swarms are up to 150 

km long. Those related to the low-relief shield plains are 

curved so that they approach being a parallel set with distance from the source, and they approach being parallel to 

the pervasive lineament fabric discussed above. Close to 

11
the source, however, the grabens are younger than the pervasive lineament fabric because locally they break up into 

en echelon segments that individually parallel the older 

fabric but which overall define the trend of the younger 

graben. The grabens from Kumang Corona fan with little 

curvature of individual structures.

WRINKLE RIDGES

As is true for most plains areas on Venus, wrinkle 

ridges are nearly ubiquitous in the Bereghinya Planitia 

quadrangle. Although local patterns are present (such as 

the arachnoid pattern described earlier), the quadrangle as 

a whole has no consistent wrinkle-ridge pattern because of 

the complexities introduced by deformation belts, corona 

structures, and the structures in the belts connecting the 

coronae into chains. In the south-central and southeastern 

parts of the quadrangle, where deformation belts are not 

present and coronae are rare, wrinkle ridges appear to be 

similar to those found in plains areas elsewhere. In the 

south, one persistent orientation is within a few degrees 

of east-west. This orientation is a continuation of the pattern in the northern part of the Sappho Patera quadrangle 

(McGill, 2000). Other trends also are present, such that 

two sets of wrinkle ridges are present at any given locality. The other trends differ from place to place, however. 

Wrinkle ridges in the southwestern part of the quadrangle 

exhibit a strong north-south trend, and wrinkle ridges 

trending northwest and northeast are present in various 

places between coronae and their linking belts. Most of 

the individual wrinkle ridges are typical, being long, sinuous, and very narrow (order of resolution limit). Some 

are wider and double, comparable to the braided wrinkle ridges in the corona chains discussed above. At one 

locality (46° N., 24° E.), wrinkle ridges clearly include a 

broader ridge on which the typical narrow, bright ridges 

occur (fig. 7). This geometry is unlike most wrinkle ridges 

on Venus, which generally do not include the broader 

ridge, but very similar to the geometry of lunar and martian wrinkle ridges (Maxwell and others, 1975; Watters, 

1988). The absence of broader ridges may be only apparent due to flank slopes too gentle to yield resolvable differences in radar backscatter. Wrinkle ridges are present 

on every plains and flow unit in the quadrangle but are 

less abundant on young materials, such as Onatah and 

valles flows, than they are on regional plains material and 

other corona flows. Thus the formation of wrinkle ridges 

must have continued throughout the interval during which 

many of the material units were emplaced.

DISCUSSION

The structural and chronological observations 

derived from geologic mapping in the Bereghinya Planitia quadrangle bear on some important tectonic issues of 

global interest. These issues include the ages of structures 

and material units relative to different sets of wrinkle 

ridges, the ages of corona flows and structures relative to 

regional plains material, the sequence of development of 

coronae, and the relation between stratigraphic age and 

apparent degradation of impact craters.

Commonly, a regionally dominant, older set of wrinkle ridges is present on Venus against which members 

of younger sets terminate in “T” intersections. In a large 

area of plains, including the plains in the Sappho Patera 

quadrangle (McGill, 1993), the dominant, and oldest, 

set trends roughly east-west. This pattern is also present 

where the plains materials of Bereghinya Planitia are not 

deformed by abundant coronae and the structural belts 

connecting coronae. This relatively simple situation is 

present in the northern part of the Sappho Patera quadrangle (McGill, 2000) but is limited to a small area in 

the south-central and southeastern part of the Bereghinya 

Planitia quadrangle; elsewhere, other structural complexities either mask the regional age pattern of wrinkle ridge 

ages or they actually destroy this age pattern.

On a global scale, coronae show remarkable variability in morphology, evolutionary sequence, age 

relative to regional plains material, and volume of associated volcanic material (Stofan and others, 1992, 1997; 

Squyres and others, 1992a; Copp and others, 1998). The 

coronae and coronalike features in the Bereghinya Planitia quadrangle include many of the morphologic types 

defined by Stofan and others (1997). They also vary 

significantly in the volume of associated flows, ranging from no associated flows to large flow fields; flows 

from Onatah Corona, for example, cover several percent 

of the area of the quadrangle. For most of the coronae, 

concentric and radial structures cut the associated flows, 

and thus most of the coronae in this quadrangle seem to 

share a common evolution from early volcanism to late 

structural disruption. In support of this relationship is the 

superposition of structures in the belts connecting coronae on corona flows. A possible exception to this consistent early volcanism is the stubby lobate flow associated 

with Ilmatar Corona, which appears superposed on the 

fracture ring defining the corona. This stubby flow may 

consist of magma more evolved than basalt, which would 

be consistent with both its morphology and its relative 

age. In addition, three coronae (Trotula, Damona, and 

Parma) have flows confined to their floors that are not 

cut by any corona structures. However, it is not clear if 

the flows are younger than the structures or if the central 

parts of the coronae have no structures.

Of major concern are the ages of corona flows and 

corona structures relative to regional plains material. 

Most corona structures are younger than regional plains 

material, although for a few coronae some structures 

cut bright plains material and are truncated by regional 

12
plains material, whereas other structures related to the 

same coronae cut regional plains material. This implies 

that the structures associated with some coronae began 

to develop before emplacement of the adjacent regional 

plains material but continued to form after emplacement 

of regional plains material. For most coronae, however, 

all deformation appears to post-date regional plains material. Relative ages of regional plains material and corona 

flows are not everywhere clear. Those corona flow fields 

that include sharply defined, radar-bright digitate flows 

provide good evidence that at least these bright flows are 

younger than regional plains material. However, most 

corona volcanics have more subtle flow forms and radar 

backscatter values similar to regional plains material, and 

locally the contacts between these volcanics and regional 

plains material appear to be gradational or uncertain. 

Good examples of uncertain contacts are on the east 

side of Beyla Corona and on the west side of Vasudhara Corona. The density of wrinkle ridges on corona 

flows and on regional plains material is similar, with the 

exception of flows from Onatah Corona, which have a 

lower density of superposed wrinkle ridges. Some of the 

material mapped as regional plains material likely was 

derived from coronae, and thus most corona flow materials are probably the same age as or younger than regional 

plains material.

Stofan and others (1997) describe three groups of 

coronae based on geologic setting: rise coronae, isolated coronae, and chasmata coronae. The coronae of 

Bereghinya Planitia are not on a rise nor on a chasma, 

but most of them are clustered together so the term “isolated” seems inappropriate for all of them except Beyla 

and Kumang. Furthermore, the sequence of volcanism 

and fracturing noted for most Bereghinya Planitia coronae, as well as the dominant morphologies, seem to fit the 

description of chasmata coronae better than the description of isolated coronae. Corona fractures and ridges for 

most coronae in Bereghinya Planitia deform regional 

plains material, whereas Stofan and others (1997) maintain that isolated coronae are generally embayed by plains 

volcanism. The coronae in this quadrangle are embayed 

by shield and valles flows but generally not by the areally dominant regional plains material, except that some 

coronae provide evidence of progressive deformation 

with some fractures embayed by regional plains material, others from the same coronae cutting regional plains 

material.

Most of the impact craters in the Bereghinya Planitia 

quadrangle are young relative to other structures. Kauffman is younger than Aušrā Dorsa, Kemble is both older 

and younger than Sigrun Fossae structures, and Elenora 

is younger than flows from Onatah Corona, which in turn 

are younger than Sigrun Fossae and Audhumla Corona. 

Prichard, Lena, Ayisatu, Noreen, Edgeworth, Browning, 

Melanka, and Mona Lisa are all superposed on wrinkle 

ridges, including the closely spaced ridges in the belts 

connecting coronae to each other. However, Stina is 

older than northwest-trending wrinkle ridges, and Ariadne yields a self-contradictory relation with east-west 

wrinkle ridges; the crater ejecta are superposed on these 

wrinkle ridges, but the digitate crater flow south of Ariadne may be cut by east-west wrinkle ridges (this relation is uncertain because a possible interpretation is that 

the crater flow found gaps and en echelon offsets in the 

wrinkle ridges and thus simply flowed around them). 

Chubado, which is younger than structures parallel to 

the trend of the elevated belt connecting Audhumla and 

Ba’het Coronae, is cut by faults transverse to the belt. 

These transverse faults are grabens radial to Kostroma 

Coronae. Kafutchi is cut by north-south-trending lineaments in the interior of Beyla Corona.

All of the craters in the quadrangle except Kafutchi, 

Chubado, and Mona Lisa have what appear to be fresh 

ejecta, and many have associated dark halos or parabolas (table 2). If post-impact volcanism degraded craters 

by burying halos, parabolas, and secondary craters and 

by embaying ejecta and flooding the floors, as has been 

suggested (Herrick and Sharpton, 2000), then one would 

expect indications of relative youth, such as secondary 

crater fields, halos, and parabolas, to be preferentially 

associated with craters having floors that are not flooded; 

that is, bright floors. Four craters have secondary crater 

fields (Lena, Mukhina, Browning, and Ferber); three of 

these have floors of intermediate backscatter, one has a 

dark floor. Edgeworth and Noreen appear to be co-sources 

for a combination parabola and streak band. Noreen has 

a bright floor, but Edgeworth has a dark floor. Overall, 

ten craters have associated halos or parabolas. Of these, 

two have bright floors, five have floors of intermediate 

backscatter, two have dark floors, and one (Elenora) is 

too small to measure floor backscatter. Where relations 

are clear, impact craters are mostly younger than wrinkle 

ridges. Only one crater, Stina, is unambiguously older 

than wrinkle ridges and it has a bright floor. Thus no evidence exists in this quadrangle for a correlation between 

crater floor brightness and apparent age or degradation 

of the crater.

GEOLOGIC HISTORY

The chronology of events and materials within the 

Bereghinya Planitia quadrangle is tied to the areally dominant material unit, regional plains material. This unit consists primarily of plains material, presumably volcanic, 

that cannot be linked to a specific source such as a corona, 

a caldera or dome, or a vallis. Regional plains material 

varies in radar backscatter and texture, but consistently 

mapping subdivisions based on these variations is not 

possible. Determining how many years were required to 

13
emplace regional plains material is not possible, nor is it 

possible to estimate the time required to emplace this unit 

relative to the time spans involved in emplacing all other 

units in the quadrangle. The absence of relative age control is a direct result of the sparse impact crater record, 

which results in the inability to separate material units in 

time by means of statistically significant differences in 

crater frequency (Campbell, 1999).

The oldest materials in the quadrangle occur as two 

mapped units: tessera and bright plains materials. Both 

occur as inliers within regional plains material, and both 

are clearly older than regional plains material because 

structures present in the inliers are sharply truncated by 

regional plains material at their contacts. Tessera material is cut by at least two trends of structures and by large 

grabens that commonly are flooded by regional plains 

material. Bright plains material is cut by only one trend 

of structures and no large grabens. Both types of inliers 

are scattered throughout the quadrangle, and thus the differences in deformation are likely due to age differences 

rather than areal differences in deformation history. Thus 

tessera material is the oldest material in the quadrangle, 

and bright plains material the next oldest. No impact craters superpose tessera and bright plains materials, and no 

other means exists to determine relative ages between 

isolated inliers. Thus determining whether either of these 

materials is of similar age throughout the quadrangle is 

not possible, nor is it possible to estimate the elapsed time 

between emplacement of tessera material and emplacement of bright plains material. In places, bright plains 

material is difficult to distinguish from regional plains 

material that is intensely deformed by closely spaced 

fractures. Thus bright plains material simply may be 

remnants of early plains material covered by later flows 

included in regional plains.

The small, unnamed ridge belt centered at 46.5° N., 

26° E. appears to be embayed by regional plains material. Most or all of the belt consists of bright plains material, consistent with the pre-regional plains material age 

implied by the embayment relation. Ridge belts on Venus 

have generally been interpreted as due to compressive 

stresses oriented normal to their trends (Barsukov and 

others, 1986; Banerdt and Golombek, 1988; Zuber, 1990; 

Solomon and others, 1992; Squyres and others, 1992b). 

Thus this small ridge belt implies an east-northeast–westsouthwest orientation of maximum compression at some 

time before emplacement of the regional plains material.

The larger areas of bright plains material generally 

occur on low, gentle hills within the plains, with regional 

plains material superposed on bright plains material 

around the periphery of the hills. The gentle slope angles 

on these hills imply that regional plains material is thin, 

at least near these exposures of bright plains material. If 

it is thin throughout the quadrangle, then the absence of 

partially buried impact craters cannot be due to burial by 

regional plains material—some other event must have 

occurred that destroyed older craters. The emplacement 

of regional plains material records a major volcanic event 

in the history of Venus, and this is true whether this event 

required a geologically brief interval (millions or tens 

of millions of years) or a lengthier interval (hundreds of 

millions of years).

Structures making up the deformation belts Sigrun 

Fossae and Aušrā Dorsa cut regional plains material, 

and thus these belts are at least in part younger than 

the emplacement of regional plains material. However, 

Sigrun Fossae structures also cut bright plains material, 

and some of these structures may be older than regional 

plains material. Although the lineaments associated 

with Aušrā Dorsa cut regional plains material, the dorsa 

ridges may be older; the evidence is equivocal. Flows 

from Belisama Vallis are partially controlled by ridges 

in Aušrā Dorsa, and flows from Bayara Vallis are superposed on structures of Sigrun Fossae. Thus these belts 

must be at least in part older than the valles flows. Flows 

from Onatah Corona also truncate peripheral structures 

of Sigrun Fossae.

The plains that form most of Bereghinya Planitia 

consist of several material units, including regional plains 

material, low-relief shield plains material, dark plains 

material, corona flows, shield flows, flows from Gula 

Mons, and valles flows. Some of these units are consistently older or consistently younger than regional plains 

material; others suggest a more complex history with several types of volcanic sources operating simultaneously.

Shield flows occur in numerous patches throughout the quadrangle. Superposition and truncation relations indicate that some of these patches are older than 

regional plains material, some younger, and some probably essentially the same age. Material derived from lowrelief shields is superposed on regional plains material, 

but in places the contacts are gradational, suggesting 

that low relief shield plains material is partly younger 

and partly the same age as material of regional plains. 

Dark plains material embays adjacent regional plains and 

thus must be at least locally younger. Flows from valles 

and from Gula Mons are entirely younger than regional 

plains material. Homogeneous plains material is probably younger than regional plains material, based on local 

control of contacts of homogeneous plains material by 

wrinkle ridges that deform regional plains material.

Relative ages of corona flows and regional plains 

material are not consistent. Many contacts between 

corona flows and regional plains material are gradational, 

implying a similar age. Locally, vague flow forms occur 

within regional plains material, and these flow materials 

may be corona derived. However, some corona flows are 

clearly superposed on regional plains material; examples 

include the radar-bright flows derived from Kostroma 

Coronae, corona f, and Cavell Corona, and all flows from 

14
Onatah Corona. Thus corona volcanism is inferred to 

overlap extensively with emplacement of regional plains 

material; some volcanism is the same age as regional 

plains material, some younger.

Cutting the regional plains in the Sappho Patera quadrangle (McGill, 2000) are pervasive fabrics of narrow, 

radar bright lineaments that are not obviously associated 

with any structural or topographic feature. One of these 

fabrics trends north-northeast, and this fabric is present 

with a north-northeast to north-south orientation on the 

plains in the southern part of the Bereghinya Planitia 

quadrangle. Farther north, this fabric is essentially lost 

amidst all the structural complexities that characterize 

most of the quadrangle. Some of the individual lineaments making up this fabric are resolvable as grabens, 

and thus this fabric implies that the earliest deformation 

to affect regional plains material was extensional with 

maximum stretching oriented roughly east-west. In addition to regional plains material, this fabric cuts shield 

flows and low-relief shield plains material; the fabric does 

not appear to be present on homogeneous plains material, dark plains material, valles flows, and flows from 

Onatah Corona, suggesting that the fabric is older than 

these units. Gula flows partially fill grabens that are part 

of this early fabric. The Gula flows are thus demonstrably 

younger than the early extensional event. Unfortunately, 

the pervasive structures associated with coronae preclude 

determining if this fabric exists on most corona flows.

All of these materials, including Onatah and valles 

flows, are deformed by wrinkle ridges. In this part of 

Venus, the earliest wrinkle ridges trend roughly eastwest (McGill, 1993, 2000), later ones have other orientations. This also is true for the southernmost part of 

the Bereghinya Planitia quadrangle, but the sequence 

elsewhere in the quadrangle is masked by younger structures. Some of the youngest materials, such as flows from 

Onatah Corona, appear to have fewer superposed wrinkle 

ridges than does regional plains material. Furthermore, 

some of the radar-bright digitate flows from coronae 

apparently are not deformed by wrinkle ridges, but this 

is somewhat ambiguous because wrinkle ridges are very 

difficult to resolve on a unit that has the same high backscatter value. Also, the emplacement of dark plains and 

homogeneous plains materials likely did not begin until 

after wrinkle ridges began to form.

Most structures related to individual coronae are 

younger than regional plains material and younger than 

flows from each corona, but older than most flows derived 

from shield fields and valles. Structures within the complex belts connecting coronae are younger than regional 

plains material. These belt structures also are younger 

than most corona flows, but they are older than flows 

from Onatah Corona, some of the bright digitate corona 

flows, and the stubby, lobate flows associated with Yaroslavna and Ilmatar Coronae. The belts connecting coronae consist of bundles of closely spaced wrinkle ridges, 

commonly astride a low ridge. This relation implies contraction normal to the belts, resulting in a seemingly chaotic stress and strain field because the belts have many 

different trends, and they connect coronae that generally 

are associated with extensional structures.

All 24 impact craters and all 6 impact splotches 

are younger than regional plains material. One crater is 

clearly younger than a young corona flow (Onatah), two 

are clearly older than corona fractures (Beyla, Kostroma), 

and two are younger than the deformation belts. About 

half of the craters are younger than wrinkle ridges, but 

one appears to be older than wrinkle ridges. The ages of 

the others relative to wrinkle ridges are unknown.

Several chronological observations are of more than 

local interest.

1. If one were to map a “plains with wrinkle ridges” 

unit, as some have done (Basilevsky and Head, 2000), 

then virtually all plains and flow units would be incorporated into this unit. What is clear from mapping this 

quadrangle is that the deformation responsible for wrinkle ridges occurred after emplacement of most material units, except for at least some impact craters. The 

lesser density of wrinkle ridges on the youngest units 

also implies that the deformation responsible for wrinkle 

ridges was progressive.

2. In some localities on Venus flows associated with 

clusters of small edifices, the shield fields of Aubele and 

others (1992), form a mappable unit that appears to be 

older than adjacent regional plains material (Basilevsky 

and Head, 2000; Bridges and McGill, 2003). This has led 

to the proposal that the volcanic style of Venus evolved 

through time from volcanics derived from many small 

edifices, through plains flood volcanism, to volcanics 

derived from a few large central volcanoes (Basilevsky 

and Head, 1998, 2000). The stratigraphy within the 

Bereghinya Planitia quadrangle does not support this 

concept because many volcanics associated with clusters 

of small edifices are clearly younger than regional plains 

material, a result that is in general agreement with results 

reported by Guest and Stofan (1999) and Addington 

(2001) from more global studies.

3. Inferring that horizontal principal stresses can be 

derived in a simple manner from trends of extensional and 

contractional structures leads to an almost chaotic pattern of stresses in this quadrangle. The earliest structures 

deforming regional plains material, roughly north-south 

fractures and east-west wrinkle ridges, are consistent 

with each other and suggest a pattern of north-south compression and east-west tension that probably affected the 

shallow crust over the entire quadrangle. However, the 

deformation belts, the belts connecting coronae, and the 

coronae themselves cannot be explained by a simple and 

areally extensive pattern of principal stresses. Some of this 

chaos could be mitigated if much of the trend variability 

15
is temporal rather than spatial, but for these major structures age differences cannot be resolved, if in fact they 

exist. Corona formation is generally related to the rise of 

thermal plumes (Squyres and others, 1992a; Smrekar and 

Stofan, 1997) followed by lateral flow of plume material and eventual downwelling after cooling. The large 

number of coronae in Bereghinya Planitia would suggest 

a swarm of plumes, and if these were active at the same 

time, or overlapped significantly in time, it is possible to 

envisage centers of uplift and extension that became coronae surrounded by zones of competing flow from several 

plumes that resulted in a complex pattern of compressive 

principal stresses. Why there should be so many plumes 

in this relatively small area is not known.

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17