AREA OF

MAP

HELLAS

PLANITIA

TYRRHENA TERRA

Hadriaca Patera

Dao Vallis

Harmakhis

Vallis

Niger Vallis

5,000

–7,000

MTM –30267

MTM –30262

Dao Vallis

+ +

+ ++++

+

+

++++

+

+

+

+

Gander

Nazca

HESPERIA PLANUM

Tyrrhena Patera

PROMETHEI TERRA

Reull Vallis

Hadriaca Patera

Peraea Cavus

Savich

Bazas

Gander

Nazca

N

Hadriaca Patera

Bazas

Peraea Cavus

Ausonia

Cavus

Torup

Ausonia Montes

Ausonia Mensa

SAVICH

20 0 20 40 60 80 100

 KILOMETERS

Planetographic latitude and west longitude coordinate system

SCALE 1:1 004 000 (1 mm = 1.004 km ) AT 270° LONGITUDE

TRANSVERSE MERCATOR PROJECTION

Prepared on behalf of the Planetary Geology and Geophysics Program, Solar 

System Exploration Division, Office of Space Science, National Aeronautics and 

Space Administration

Edited by Jan L. Zigler; cartography by Darlene A. Ryan

Manuscript approved for publication July 17, 2006

Descriptions of nomenclature used on map are listed at http://planetarynames.wr.usgs.gov/

270°

–32.5°

260°

Prepared for the

National Aeronautics and Space Administration

Scientific Investigations Map 2936

Atlas Of Mars: MTM –30262 and –30267 Quadrangles

U.S. Department of the Interior

U.S. Geological Survey

–27.5°

–32°

–31°

–30°

–29°

–28°

–27.5°

–32.5°

–32°

–31°

–30°

–29°

–28°

261° 262° 263° 264° 266° 265° 267° 269 268° 270° °

269° 268° 267° 266° 265° 264° 263° 262° 261° 260°

Surficial

Material

Vallis

Material

Hadriaca

Patera

Material

Tyrrhena

Patera

Material

Plateau and

Mountain

Material

Crater

Material

AMAZONIAN NOACHIAN HESPERIAN

CORRELATION OF MAP UNITS

PERIOD

DESCRIPTION OF MAP UNITS

SURFICIAL MATERIAL

Talus material (Middle Amazonian or younger)—Deposits border mountainous material (unit Nm) of Ausonia Mensa and extend as far as ~10 km from them. Occurs 

where mountainous material is steep. Some linear features observed at margins of unit. 

Interpretation: Debris shed from steep blocks of uplifted crust. Linear features may 

indicate fluvial or mass-wasting processes

VALLIS MATERIAL

Vallis floor material (Early Amazonian to Late Hesperian)—Smooth material, containing isolated blocks 0.5–2 km across, forms floors of depressions bordered by steep 

scarps. Interpretation: Sedimentary deposits forming floors of collapse depressions in 

water- or ice-rich materials

Irregular vallis floor material (Early Amazonian to Late Hesperian)—Commonly low 

lying deposits have smooth, low-relief surfaces dissected by small (~0.5–2.5 km wide) 

channels and troughs. Interpretation: Sedimentary and volcanic deposits (units AHtf, 

Hhfl, Hpl3) modified by fluvial erosion in initial stages of dissection and collapse

HADRIACA PATERA MATERIAL

Hadriaca Patera caldera-filling material (Late Hesperian or younger)—Smooth, 

relatively featureless deposits partly fill depression at summit of Hadriaca Patera and 

have well-defined boundary at west margin. Scarps occur along margins of unit and 

extend into surrounding materials. Interpretation: Volcanic materials (lava flows or 

pyroclastic deposits) filling Hadriaca Patera caldera. Some scarps may represent flow 

margins. Unit contained within caldera to west and may overflow caldera to north and 

east. Unit represents late-stage volcanic activity at Hadriaca Patera

Hadriaca Patera upper flank material (Early Hesperian)—Material exhibiting 

relatively smooth surface surrounding caldera-filling material (unit Hhc) at Hadriaca 

Patera. Bordered by scarps. Several layers exposed to northwest. Material is relatively 

continuous to north and extends more than 100 km from caldera margin; to southwest, 

unit consists of topographically high remnants forming ridges within Hadriaca Patera 

lower flank material (unit Hhfl). Interpretation: Volcanic deposits (probably pyroclastic flows) erupted from caldera at Hadriaca Patera and later dissected by fluvial 

processes. Erosional morphology indicated by presence of layering and scarps. 

Morphologic differences between upper and lower flank materials attributed to 

changes in topography and position relative to caldera and to resulting changes in 

degree of erosion

Hadriaca Patera lower flank material (Early Hesperian)—Layered, dissected material 

surrounding caldera-filling material (unit Hhc) and upper flank material (unit Hhfu) 

at Hadriaca Patera. Pattern of dissection radial to caldera. Numerous scarps; some 

channels and ridges. Spacing between ridges is smaller and more layers are exposed 

to south and west than to north and east of caldera. Interpretation: Volcanic deposits 

(probably pyroclastic flows) erupted from caldera and later dissected by fluvial 

processes. Erosional morphology indicated by layering and remnant mesas. 

Decreased spacing of scarps reflects greater slope and resulting change in degree of 

erosion

TYRRHENA PATERA MATERIAL

Tyrrhena Patera flank flow material (Early Amazonian to Late Hesperian)—Forms 

deposits with rough surface containing lobate scarps and channels bounded by levees. 

Lobes elongated to southwest. Unit extends from Tyrrhena Patera (northeast of map 

area) for over 1,000 km to southwest. Some ridges observed. Embays mountainous 

material (unit Nm) and dissected unit of the plateau sequence (unit Npld) along its 

west margin in MTM –30262 and covers smooth unit of the plateau sequence (unit 

Hpl3) near Ausonia Mensa and Ausonia Montes. Interpretation: Lava flows displaying lobate margins, lava channels, and possibly partially collapsed lava tubes form 

extensive lava flow field associated with Tyrrhena Patera. Some ridges may be associated with flow emplacement and may be partially volcanic

PLATEAU AND MOUNTAIN MATERIAL

Smooth unit of the plateau sequence (Early Hesperian)—Forms flat, relatively featureless plains that fill basins and locally embay dissected unit of the plateau sequence 

(unit Npld) and mountainous material (unit Nm). Some ridges and scarps observed. 

Interpretation: Sedimentary deposits and volcanic materials that fill depressions and 

cover underlying rocks

Dissected unit of the plateau sequence (Late to Middle Noachian)—Forms cratered 

surfaces of moderate to high relief with some relatively smooth areas; dissected by 

small channels and troughs. Interpretation: Materials formed during interval of 

intense cratering. Probably composed of impact breccia and volcanic and erosional 

deposits, modified by fluvial and mass-wasting processes

Mountainous material (Late to Middle Noachian)—Forms large, rugged, isolated 

blocks. Also occurs as remnants of large crater rims. Scattered, smaller, less-rugged 

deposits surrounded by smooth plateau unit (unit Hpl3). May have channels extending 

downslope to margin of unit. Interpretation: Ancient crustal material uplifted during 

period of heavy impact cratering. May include remnants of large crater rims. Channeling on slopes indicates modification by mass-wasting or fluvial processes

CRATER MATERIAL

[Craters and their associated rim and ejecta materials are assigned to three classes based upon their 

state of degradation and stratigraphic relations. Craters having rim crest diameters ≥3 km across are 

shown on the map. Crater materials are subdivided where floor, rim, and ejecta materials can be identified.]

Crater floor material (Late Amazonian to Late Noachian)—Forms typically smooth, 

featureless surfaces in crater interiors; in places, may exhibit scarps or channels. 

Interpretation: Sedimentary deposits of mass-wasting and aeolian origin that 

accumulate on crater floors; contributions of fluvial, glacial, and lacustrine sediments 

also possible

Well-preserved crater material (Late to Early Amazonian)—Pronounced, continuous 

crater rim that rises above surrounding materials has steep inner wall and generally 

well defined, continuous ejecta deposit. Crater floors are typically smooth and featureless and, in places, may exhibit scarps or channels. Interpretation: Youngest crater 

materials with minimal degradation. Crater floor may be covered by sedimentary 

deposits (unit cf) that are, in places, dissected by channels or faults 

Ejecta material—Generally well defined, continuous deposits surrounding crater rim 

material (unit cr3). Example at Bazas crater north of Hadriaca Patera

Rim material—Continuous deposits encircling and rising above crater floor, including 

crater wall inside rim crest. Example at Bazas crater north of Hadriaca Patera 

Moderately degraded crater material (Early Amazonian to Early Hesperian)—Crater 

rim may exhibit only minor relief above surrounding materials. Ejecta deposits absent 

or discontinuous and poorly exposed; crater floors typically smooth and featureless; in 

places, may exhibit scarps or channels. Interpretation: Crater materials of moderate 

age and degradation state. Rim is partially eroded; ejecta may be completely eroded; 

crater floor may be covered by sedimentary deposits (unit cf). In places, dissected by 

channels or faults

Ejecta material—Discontinuous or poorly exposed deposits that are adjacent to crater 

rim material (unit cr2); large exposure in northwest corner of MTM –30267 is ejecta 

blanket from crater Isil, an ~80-km-diameter crater partly located in MTM –30272 and 

MTM –25272 northwest of map area. Examples at Gander and Nazca craters on southeast flanks of Hadriaca Patera

Rim material—Continuous to discontinuous deposits encircling and, in places, rising 

above crater floor, including crater wall inside rim crest. Examples at Gander and 

Nazca craters on southeast flanks of Hadriaca Patera

Highly degraded crater material—Crater rim subdued or discontinuous and generally 

does not exhibit external relief; ejecta deposits not observed. Inner crater wall may 

exhibit scarps and channels; crater floors typically smooth and featureless but, in 

places, may exhibit scarps or channels. Interpretation: Oldest, most degraded crater 

materials. Ejecta is completely eroded; rim trace may be evident but rim nearly eroded 

to level of surrounding materials; crater floor may be covered by sedimentary deposits 

(unit cf), in places dissected by channels or faults

Rim material (Early Hesperian to Middle Noachian)—Generally subdued, discontinuous deposits adjacent to crater floor material exhibiting little or no relief. Includes 

crater wall inside rim crest. May exhibit scarps or channels. Example at Torup crater 

adjacent to Ausonia Montes

Contact—Dashed where approximately located

Ridge crest

Scarp—Hachures point downscarp

Channel

Volcanic channel

Margin of volcanic flow—Hachures point downslope

Small dome or hill

Crater rim crest

Crater central peak—Hachures point downslope

Closed depression

INTRODUCTION

Mars Transverse Mercator (MTM) –30262 and –30267 quadrangles cover the summit region and 

east margin of Hadriaca Patera, one of the Martian volcanoes designated highland paterae (Plescia and 

Saunders, 1979). MTM –30262 quadrangle includes volcanic deposits from Hadriaca Patera and 

Tyrrhena Patera (summit northeast of map area) and floor deposits associated with the Dao and Niger 

Valles canyon systems (south of map area; figs. 1, 2). MTM –30267 quadrangle is centered on the 

caldera of Hadriaca Patera (fig. 3). The highland paterae are among the oldest, central-vent volcanoes 

on Mars (Scott and Carr, 1978) and exhibit evidence for explosive eruptions, which make a detailed 

study of their geology an important component in understanding the evolution of Martian volcanism. 

Photogeologic mapping at 1:500,000 scale from analysis of Viking Orbiter images complements volcanological studies of Hadriaca Patera, geologic investigations of the other highland paterae, and an 

analysis of the styles and evolution of volcanic activity east of Hellas Planitia in the ancient, cratered 

highlands of Mars (Greeley and Crown, 1990; Crown and Greeley, 1993). This photogeologic study is 

an extension of regional geologic mapping east of Hellas Planitia (Crown and others, 1992; Mest and 

Crown, 2001).

The Martian highland paterae are low-relief, areally extensive volcanoes exhibiting central calderas and radial channels and ridges (Plescia and Saunders, 1979; Greeley and Spudis, 1981). Four of 

these volcanoes, Hadriaca, Tyrrhena, Amphitrites, and Peneus Paterae, are located in the ancient 

cratered terrains surrounding Hellas Planitia and are thought to be located on inferred impact basin 

rings or related fractures (Peterson, 1978; Schultz, 1984). Based on analyses of Mariner 9 images, 

Potter (1976), Peterson (1977), and King (1978) suggested that the highland paterae were shield volcanoes formed by eruptions of fluid lavas. Later studies noted morphologic similarities between the 

paterae and terrestrial ash shields (Peterson, 1978; Francis and Wood, 1982) and the lack of primary 

lava flow features on the flanks of the volcanoes (Greeley and Crown, 1990; Crown and Greeley, 

1993). The degraded appearances of Hadriaca and Tyrrhena Paterae and the apparently easily eroded 

materials composing their low, broad shields (Greeley and Spudis, 1981; Crown and Greeley, 1993) 

further suggest that the highland paterae are composed predominantly of pyroclastic deposits. Analyses of eruption and flow processes indicate that the distribution of units at Hadriaca and Tyrrhena 

Paterae is consistent with emplacement by gravity-driven pyroclastic flows (Crown and others, 1988; 

Greeley and Crown, 1990; Crown and Greeley, 1993). Detailed geologic study of the summit caldera 

and flanks of Hadriaca Patera is essential to determine the types of volcanic materials exposed, the 

nature of the processes forming these deposits, and the role of volcanism in the evolution of the 

cratered highlands that are characteristic of the southern hemisphere of Mars.

GENERAL GEOLOGY

The area east of Hellas Planitia is a complex geologic region affected by volcanism, tectonism, 

and channel- and canyon-forming processes (Crown and others, 1992; Tanaka and Leonard, 1995; 

Gregg and others, 1998; Price, 1998; Leonard and Tanaka, 2001; Mest and Crown, 2001; Crown and 

others, 2005b). The Hadriaca Patera summit region is dominated by the central caldera and eroded 

flanks of the volcano. North and west of its summit, Hadriaca Patera is bordered by older plateau and 

mountainous materials, including the rugged rim materials of Savich and Torup craters, Ausonia 

Montes, and Ausonia Mensa. The southeast flanks of Hadriaca Patera and the adjacent plains are cut 

by Dao and Niger Valles, which extend to the southwest into Hellas Planitia. The collapse depressions 

of Ausonia Cavus and Peraea Cavus define their uppermost extents. Plateau and mountainous materials to the north and east of Hadriaca Patera are embayed by an extensive flank flow unit that extends 

from the summit area of Tyrrhena Patera and contains numerous lava flow lobes. Many impact craters, 

such as Gander, Nazca, and Bazas on or adjacent to Hadriaca Patera and Savich and Torup to the northeast, are apparent throughout the map area; some exhibit smooth, flat floors indicating modification 

and infilling by sedimentary processes (Mest and Crown, 2005, 2006; Moore and Howard, 2005).

STRATIGRAPHY

We identified and mapped geologic units in MTM –30262 and –30267 quadrangles, based on 

analyses of morphologic characteristics in Viking Orbiter images. We determined stratigraphic 

positions, based on superposition, cross-cutting, and embayment relations, as well as crater 

size-frequency distributions. Geologic unit descriptions are based on photogeologic analyses of Viking 

Orbiter images and examination of recently acquired Mars Global Surveyor Mars Orbiter Camera 

(MOC) and Mars Odyssey Thermal Emission Imaging System (THEMIS) images.

The oldest units in the area are mountainous material (unit Nm) and the dissected unit of the 

plateau sequence (unit Npld; Greeley and Guest, 1987). Noachian mountainous material forms large, 

rugged blocks that rise above the surrounding plains, such as those exposed in Ausonia Montes and 

Ausonia Mensa. Other exposures of mountainous material appear to be remnants of large impact crater 

rims, such as Savich Crater. This material was uplifted and emplaced during an interval of intense 

cratering early in Martian history, and many exposures may have been associated with the formation 

of the impact basin that now contains Hellas Planitia. At the margins of many mountains, channels or 

gullies indicate modification by mass-wasting or fluvial processes. In MTM –30262 quadrangle, 

smooth material forms aprons of debris on the south side of Ausonia Mensa (fig. 4). These aprons are 

composed of talus material (unit At) shed from steep slopes and may be among the youngest landforms 

in the region. The Noachian dissected plateau unit (Npld), both in Ausonia Mensa and between 

Ausonia Montes and Torup crater, exhibits heavily cratered surfaces but contains some smooth areas 

and regions dissected by small channels and troughs approximately 0.5–2.5 km wide. This unit is 

typical of the cratered highlands of Mars and is found throughout the southern hemisphere.

The Hesperian smooth unit of the plateau sequence (unit Hpl3) forms flat, relatively featureless 

plains filling low-lying areas adjacent to the older plateaus and mountainous regions and constitutes a 

widespread unit that typifies modification of the heavily cratered highlands (fig. 4; Greeley and Guest, 

1987). Surface features include ridges and scarps. THEMIS images show that surface features mapped 

from Viking Orbiter images include ridges of apparent tectonic origin, erosional scarps, and margins 

of flow lobes that are similar to those mapped in the Tyrrhena Patera flank flow unit (AHtf). The 

smooth unit of the plateau sequence in the map area is composed of fluvial and aeolian sedimentary 

deposits and volcanic flows that fill the interior of Savich Crater and that are adjacent to Bazas and 

Torup craters, Ausonia Montes, Ausonia Mensa, Ausonia Cavus, and Peraea Cavus.

Hadriaca Patera flank materials, which surround the caldera, are divided into two units: Hadriaca 

Patera upper flank material (unit Hhfu) and Hadriaca Patera lower flank material (unit Hhfl). The 

upper flank material is proximal to Hadriaca Patera caldera-filling material (unit Hhc) and is bordered 

by scarps (fig. 3). Upper flank material forms a plateau that is relatively continuous to the north, 

extending more than 100 km from the caldera rim. Several layers are exposed northwest of the caldera 

in upper flank material, although the surface of upper flank material is generally smoother than that 

of lower flank material in Viking Orbiter images. South and west of the caldera, upper flank material 

consists of topographically high remnants that form the materials capping ridges within Hadriaca 

Patera lower flank material. Hadriaca Patera lower flank material consists of layered, dissected 

deposits underlying Hadriaca Patera upper flank material and surrounding Hadriaca Patera calderafilling material. Numerous scarps define multiple layers within these deposits and bound the ridges 

between channels, which are oriented radially to the caldera (fig. 5). Isolated mesas that are also 

aligned in a radial pattern to the caldera are observed both adjacent to the caldera and farther down 

the flanks and indicate that the ridges are erosional remnants of the upper and lower flank materials 

(Crown and Greeley, 1993).

Hadriaca Patera, which has dimensions of approximately 300 by 560 km, is dominated by its 

channeled flanks, which are elongated to the southwest along the regional slope from Hesperia Planum 

to Hellas Planitia. Flank slopes estimated from Viking data range from approximately 0.09° in the 

north to approximately 0.47° in the west and south, where the spacing between channels is smaller and 

the number of exposed layers is greater than to the north (Crown and Greeley, 1993). Slopes derived 

from Mars Orbiter Laser Altimeter (MOLA) 128 pixels/degree, gridded data confirm the low slopes 

(<1°) for Hadriaca Patera’s flanks and show that to the northwest the flanks actually slope upward 

slightly (~0.25°; fig. 3). Given the magnitude and extent of subsidence inferred around Dao and Niger 

Valles (Crown and others, 2004, 2005b), it is possible that Hadriaca Patera has subsided as well. The 

asymmetry of the flank slopes could be partly explained by increasing subsidence from the summit 

region to the south toward Dao Vallis. Within the north flanks of Hadriaca Patera, the observed scarps 

do not form a distinct radial pattern and only a few layers are evident within the units. The morphologic 

differences observed in the channeled flanks of Hadriaca Patera, as well as the differences between 

Hadriaca Patera upper flank material (unit Hhfu, most prevalent in the north) and Hadriaca Patera 

lower flank material (unit Hhfl), are attributed to changes in topography and the resulting changes in 

the degree of erosion, rather than to significant material differences as a consequence of changes in 

composition or emplacement style (Crown and Greeley, 1993).

The channels contained within the flanks of Hadriaca Patera are degraded, trough-shaped valleys 

that lack tributaries (Gulick and Baker, 1990; fig. 5). Theater heads are observed both adjacent to the 

caldera and on the southwest flanks. Many of the channels are continuous for long distances; however, 

some channels are discontinuous and others emanate from local topographic highs (crests of the ridges) 

on the flanks. Evidence for channel widening and the existence of theater heads indicates that groundwater sapping may have enlarged the channels (Gulick and Baker, 1990). On the southwest flanks, 

small V-shaped channels in the central parts of the larger troughs suggest dissection by surface runoff 

(Crown and Greeley, 1993). The morphology of the channels and related scarps and the presence of 

remnant mesas indicate that Hadriaca Patera exhibits an erosional surface morphology; the inferred 

friable nature of the materials within the flanks of Hadriaca Patera is also consistent with the volcano 

being composed of pyroclastic deposits (Crown and Greeley, 1993; Crown and others, 1992). No 

primary effusive volcanic features are evident on the flanks of Hadriaca Patera in Viking Orbiter 

images.

Analyses of MOC narrow-angle and THEMIS visible (VIS) and infrared (IR) images of the upper 

and lower flank materials of Hadriaca Patera support Viking-based interpretations of a dissected volcanic surface that lacks primary flow features. THEMIS images show that well-defined ejecta blankets 

associated with craters approximately 5–15 km in diameter superpose both the locally high standing 

flank materials (units Hhfu, Hhfl) and the floors of adjacent erosional valleys (Crown and others, 

2005a; Williams and others, 2005). This suggests that both the formation and the main period of dissection of the flank materials were ancient, as constrained by crater counts from Viking Orbiter images 

(table 1). The limited dissection of some of these ejecta blankets by V-shaped inner channels in the 

wider radial valleys and the presence of fine-scale troughs perpendicular to radial valleys at the south 

margin of Hadriaca Patera suggest sustained or renewed erosion of the patera flanks, at least in some 

localities (Crown and others, 2005b).

The caldera-filling material (unit Hhc) at Hadriaca Patera exhibits smooth, relatively featureless 

surfaces (fig. 3). The caldera is approximately 77 km across. The caldera wall is well defined to the 

west, whereas a north or east caldera rim is not apparent, possibly due to either overflow or mantling 

by volcanic materials. The eastern caldera floor is topographically higher than the remainder of the 

caldera floor, and its surface exhibits many small (<2 km across), dome-like features that could be 

either erosional remnants of an ash deposit or lava flow or constructional volcanic landforms, such as 

lava domes or cones. In Viking Orbiter images, their origin is unclear; in MOC narrow-angle and 

THEMIS VIS images, many of these dome-like features appear buried or degraded, without clear 

preservation of their primary volcanic morphology. Scarps are evident within the caldera and extend 

into the surrounding flanks of the volcano. Although most of the scarps appear to be erosional, some 

may be degraded tectonic features, and a large scarp near the southwest margin of the caldera may be 

a flow margin of ponded lavas.

Based on morphological characteristics, the flanks of Hadriaca Patera consist of eroded pyroclastic deposits, with potential effusive activity subsequently producing caldera-filling deposits. Gravitydriven flow models demonstrate that the distribution of flank materials may be attributed to the 

emplacement of pyroclastic flows (Crown and Greeley, 1993). Layering, exposed within the flank 

materials by groundwater sapping and runoff, may be the result of different degrees of welding. From 

an energy perspective, both magmatic and hydromagmatic eruption models are viable (Crown and 

Greeley, 1993). Geomorphic analyses and mapping indicate an extended and complex history of 

volatile-driven activity in the region surrounding Hadriaca Patera (Crown and others, 1992; Mest and 

Crown, 2001; Crown and others, 2005b). The regional geologic setting and analyses of the potential 

supply of groundwater are consistent with hydrovolcanic activity (Crown and Greeley, 1993). Similarities in flank materials suggest that Tyrrhena and Hadriaca Paterae had comparable volcanic and 

erosional histories; however, Tyrrhena Patera exhibits evidence for greater structural modification at its 

summit than Hadriaca Patera and for extensive effusive activity on its southwest flank (Greeley and 

Crown, 1990). The V-shaped channels observed in the central parts of the larger valleys within 

Hadriaca Patera’s flanks suggest a greater degree of runoff relative to Tyrrhena Patera, which is consistent with evidence for enhanced (and younger) volatile-driven activity in proximity to Hadriaca Patera 

(Crown and others, 2005b).

The eastern part of MTM –30262 quadrangle is dominated by a distinctive flank flow unit (unit 

AHtf) that extends from Tyrrhena Patera. This unit contains many flow lobes and leveed channels (fig. 

4). Some of the channels are discontinuous and may represent partly collapsed lava tubes. The flow 

lobes within the flank flow unit are elongated to the southwest, and some are longer than 100 km. 

Morphologic similarities to terrestrial basaltic lava flows suggest similar eruptive conditions (Crown 

and others, 1991). The entire flank flow unit extends more than 1,000 km from the summit area of 

Tyrrhena Patera to the southwest. Near Hadriaca Patera, the flank flow unit embays the rugged massif 

of Ausonia Mensa (units Nm, Npld) and covers the smooth unit of the plateau sequence (unit Hpl3). 

The flank flow unit merges with channeled plains east of Hellas Planitia, which is south of MTM 

–30262 quadrangle. The lava flows within this unit are definitive evidence for effusive volcanic deposits associated with the highland paterae (Greeley and Crown, 1990; also Moore and Thompson, 1991). 

Many ridges are observed within this unit, and some appear to have flows extending along or from 

them (Porter and others, 1991). Dominant ridge trends within the entire flank flow unit include orientations both radial and concentric to Hellas Planitia (Crown and others, 1992).

Many channels are evident within the geologic materials in MTM –30262 and –30267 quadrangles. Channels that are interpreted to be volcanic in origin are found within volcanic units, often in 

the centers of lava flow lobes. These channels appear to be high standing and constructional, rather 

than erosional. Typically, volcanic channels may also have segments that exhibit partial collapse of 

roof materials. Volcanic channels are differentiated from other channels on the map. Other channels in 

the region are attributed to fluvial and mass-wasting processes. Some channels represent fluvial activity, because they appear to be parts of larger drainage systems, dissect the local surface, and are sometimes directly associated with Dao or Niger Vallis. Evidence of fluvial deposition or of features specifically diagnostic of fluvial erosion is not observed in Viking Orbiter images. Analyses of MOC images 

of parts of Dao and Niger Vallis show that lineations interpreted to be scour marks due to fluvial 

erosion in Viking Orbiter images are actually the result of collapse and breakdown of plains materials 

(Crown and others, 2004).

The east and southeast flanks of Hadriaca Patera and the west margin of the flank flow unit are 

dissected by the Dao and Niger Valles canyon systems. Dao and Niger Valles are parallel canyon 

systems that merge south of Hadriaca Patera and may have both surface and subsurface connections 

along east and southeast margins of Hadriaca Patera. Vallis floor material (unit AHv) is observed in 

two smooth-floored, steep-walled depressions (Peraea Cavus and Ausonia Cavus) that represent the 

upper reaches of the canyon systems. Small knobs on their floors may be remnants of collapsed plains 

or accumulations of sedimentary material. In Viking Orbiter images, no layering in canyon walls or 

interior layered deposits are observed. MOLA topographic profiles show that the depressions are a 

kilometer or more deep and deepen toward their centers (Crown and Mest, 2001). MOC images show 

that the floors of the depressions exhibit smooth, knobby, and hummocky surfaces. Dune forms are 

present and are concentrated in local low-lying regions, and the upper parts of the walls are layered. In 

Ausonia Cavus, small layered and rounded hills are presumably slump blocks of surrounding plains 

material.

Peraea Cavus and Ausonia Cavus are separated from the main canyons of Dao and Niger Valles 

(south of map area) by zones of collapsed and subsided plains (Squyres and others, 1987; Crown and 

others, 1992; Mest and Crown, 2001; Crown and others, 2004). These materials are mapped as irregular vallis floor material (unit AHvi), which exhibits surfaces dissected by small channels and troughs. 

We interpret irregular vallis floor material as volcanic flank materials and smooth plateau material that 

have undergone the initial stages of dissection and collapse. Parts of their surfaces clearly exhibit 

characteristics of the surrounding plains, whereas other areas of plains material appear to have been 

significantly altered by some combination of collapse, erosion, and deposition. MOLA topographic 

data show subsided plains as much as 500 m below surrounding materials, although the magnitude of 

subsidence is typically less and shows a high degree of spatial variability (Crown and others, 2004).

Vallis floor material (unit AHv) denotes regions where pre-existing materials were almost 

completely removed by a combination of surface and subsurface flow (Squyres and others, 1987; 

Crown and others, 1992). The canyon floor in these areas is presumably depositional. While the 

relative ages between the valles materials are poorly constrained, the incomplete dissection of the 

irregular vallis floor material suggests that it is older than the vallis floor material. Evidence for subsurface flow and collapse in association with Dao and Niger Valles suggests that the near-surface materials in this region are water or ice rich (Crown and others, 2004, 2005b).

Craters and their associated rim and ejecta materials are divided into three classifications based 

upon their state of degradation and stratigraphic relations: (1) well-preserved crater material (unit c3) 

exhibits pronounced, continuous crater rims, steep inner walls, and generally well defined, continuous 

ejecta deposits; (2) moderately-degraded crater material (unit c2) displays partially eroded rims and 

may have only poorly exposed, discontinuous ejecta deposits; and (3) highly degraded crater material 

has subdued and (or) discontinuous rims and generally has no recognizable ejecta deposits. Only 

craters with rim-crest diameters greater or less than 3 km are mapped. For each classification, crater 

rim material and crater ejecta material are mapped where possible. The blocky, rugged material 

forming the inner and outer rims of impact craters is designated crater rim material (units cr1, cr2, cr3), 

and the rough-textured deposits surrounding crater rims and subduing or mantling the underlying 

topography are crater ejecta material (units ce2, ce3). Some crater ejecta deposits have bounding 

scarps and appear to have been emplaced as fluid flows. Ejecta from the crater Isil embays plateau and 

mountain material and the northwestern margin of Hadriaca Patera in the northwest corner of MTM 

–30267. This ejecta blanket is mapped as unit ce2; whereas, Mest and Crown (2006) map Isil ejecta as 

unit c3 based on the presence of discrete ejecta flow lobes observed adjacent to the crater rim (outside 

the map area). In Viking Orbiter images, crater floor material (unit cf) consists of smooth deposits 

filling craters and may contain some scarps and channels. Crater floor material may have diverse 

origins, and we interpret it as sedimentary deposits, most likely emplaced by mass-wasting or aeolian 

processes; contributions of glacial, fluvial, and lacustrine sediments are also possible. Crater floor 

material may be similar in age to or significantly younger than the formation of the crater in which it 

is found. Crater central peaks, mapped as crater floor material, consist of knobby or hilly materials 

found on crater floors. A central peak is observed in Gander crater (~35 km diam) southeast of the 

Hadriaca Patera caldera.

GEOLOGIC HISTORY

The geologic history of the Hadriaca Patera summit region is derived primarily from analysis of 

Viking Orbiter images and supplemental information from MOLA topographic data and MOC and 

THEMIS images. The evolution of the region and the relative ages of the units are supported by crater 

size-frequency distributions presented in the regional study of Crown and others (1992; table 1). The 

observed types of geologic materials, the geomorphologic characteristics of the units, and the apparent 

stratigraphic relations suggest the following sequence of events in order of occurrence:

1. Uplift of Noachian mountains and plateau materials (units Nm, Npld) in association with and 

following the impact event centered in the location of Hellas Planitia. Materials are preserved as 

isolated massifs and heavily cratered terrain that contain remnants of large crater rims (unit cr1).

2. Dissection of the Noachian upland materials and emplacement of Hesperian smooth unit of the 

plateau sequence (unit Hpl3), involving sedimentary and volcanic processes.

3. Formation of Hadriaca Patera, including the central caldera. Flank materials (units Hhfu, Hhfl) 

are interpreted as pyroclastic deposits, presumably emplaced as flows. Both explosive and effusive 

eruptive activity may have contributed to formation of the caldera deposits (unit Hhc).

4. Erosion of the flanks of Hadriaca Patera, presumably by groundwater sapping and localized 

surface runoff along the south flanks of the volcano.

5. Emplacement of the lava flows and lava channels from Tyrrhena Patera (unit AHtf). Ridges 

formed by compression after and, possibly, during flow emplacement; some ridges may be partially 

volcanic and delineate source vents for lava flows. Contractional deformation also affects Hadriaca 

Patera flank materials (units Hhfu, Hhfl) and the smooth unit of the plateau sequence (unit Hpl3).

6. Formation of Dao and Niger Valles. Fluvial activity may include groundwater sapping, subsurface flow, and local surface runoff. Collapse and removal of material is indicated by the morphology 

of vallis floor materials (units AHv, AHvi); Peraea and Ausonia Cavi provide evidence for formation 

of discrete collapse features at upper extents of Dao and Niger Valles, with subsurface connections to 

the main parts of the canyon systems.

7. Talus deposits (unit At) shed from the steep south side of Ausonia Mensa.

8. Impact events that produce crater materials (units c2, c3; ejecta and rim subunits) during and 

subsequent to the previous events. Sediment accumulates on the floors of some craters (unit cf) due to 

a variety of degradational processes.

ACKNOWLEDGMENTS

This research was supported by the NASA Planetary Geology and Geophysics Program. Helpful 

reviews were provided by Ted Maxwell and Jim Zimbelman. We thank Les Bleamaster for assistance 

with figure preparation. MOC images courtesy of National Aeronautics and Space Administration 

(NASA), Jet Propulsion Laboratory (JPL), and Malin Space Science Systems. THEMIS images 

courtesy of NASA, JPL, and Arizona State University. MOLA data courtesy of NASA Goddard Space 

Flight Center.

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Tyrrhena Patera region of Mars: U.S. Geological Survey Miscellaneous Investigations Series 

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Journal of Geophysical Research, v. 100, p. 5407–5432.

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Geologic Map of MTM –30262 and –30267 Quadrangles, Hadriaca Patera Region of Mars

By

David A. Crown1 and Ronald Greeley2

2007

Figure 1. MOLA DEM (128 pixels/degree) of northeastern Hellas Planitia and Hesperia Planum, 

Mars, showing map area (MTM –30262 and –30267 quadrangles). Locations of highland paterae, 

canyon systems, and major physiographic provinces are indicated.

Figure 2. Perspective view of MOLA DEM (128 pixels/degree) of summit region of Hadriaca 

Patera, showing low relief of volcano, dissected patera flanks, and topographic depressions associated with parts of Dao and Niger Valles systems (fig. 1). Northwest of ~77 km-diameter caldera, 

patera flanks slope slightly uphill and appear to be confined by remnant of rugged crater rim. View 

to northeast; vertical exaggeration x 10.

0 25 KILOMETERS

Figure 3. Viking Orbiter image (410S02, 166 m/pixel resolution) of summit caldera of Hadriaca Patera. The morphology of 

the west rim is indicative of collapse; to the north and east, the 

rim may be covered by volcanic materials. Small dome-like 

features (d) are observed on the surface of Hadriaca Patera 

caldera-filling material (unit Hhc) in the eastern part of the 

caldera. Erosional scarps are apparent; some incise the caldera 

rim. A large scarp (arrow) in the southwest may be the margin 

of ponded lavas. Hadriaca Patera lower flank material (unit 

Hhfl) is visible south and west of the caldera. A plateau of 

Hadriaca Patera upper flank material (unit Hhfu) surrounds the 

caldera to the west and north. North is toward the upper right.

0 20 KILOMETERS

Figure 5. Viking Orbiter image (408S67, 108 m/pixel resolution) of the channeled flanks of Hadriaca Patera. The channels 

are trough-shaped valleys extending radially from the summit 

caldera. Layers are exposed in channel walls (arrows). Note 

theater-headed valleys indicative of groundwater sapping (h) 

and V-shaped runoff channels (rc) in the centers of some 

valleys. Erosional remnant mesas (m) are evident within 

Hadriaca Patera lower flank material (unit Hhfl). North is 

toward the upper right.

0 25 KILOMETERS

Figure 4 (left). Viking Orbiter image (411S02, 103 m/pixel resolution) 

showing an isolated massif (Ausonia Mensa) to the east of Hadriaca Patera 

that consists of a combination of mountainous material (unit Nm) and the 

dissected unit of the plateau sequence (unit Npld). On the north side, numerous parallel channels form on relatively shallow slopes, presumably by a 

combination of mass-wasting and fluvial processes. On the steeper south 

side, talus material (unit At, arrows) covers the contact between the mountainous material (unit Nm) and the surrounding plains (unit Hpl3). Part of a 

discontinuous leveed channel is observed at the center of a flow lobe (fl) in 

the Tyrrhena Patera flank flow unit (unit AHtf), whose flows superpose unit 

Hpl3 at the bottom center of the image. Ausonia Mensa and the surrounding 

plains exhibit a series of medium-sized craters with a range of degradation 

states (see crater materials in Description of Map Units). North is toward the 

upper right.

Table 1. Crater size-frequency data and relative age determinations for geologic units in the 

Hadriaca Patera region of Mars.

[Data from regional study (Crown and others, 1992) of MTM –30262, –30267, –30272, –35262, –35267, –35272, 

-40262, –40267, and –40272 quadrangles; total number of craters and area represent entire unit exposures within these 

nine quadrangles. N(2), N(5), and N(16) are cumulative number of craters >2, >5, and >16 km in diameter per 106 km2; 

error = ± [(n(x)1/2)/A] x 106, where n = number of craters > x km in diameter and A = area. Age range is based on 

superposition relations and crater counts using the crater-density boundaries of Tanaka (1986): EA, Early Amazonian; 

LH, Late Hesperian; EH, Early Hesperian; LN, Late Noachian; MN, Middle Noachian]

 Unit Total no. Area Age range

 label craters (km2) N(2) N(5) N(16) (epoch)

AHvt1 56 45,947 239±72 109±49 0 EA–LH

Hhc 10 5,744 174±174 0 0 LH or younger

AHtf 188 80,576 397±70 87±33 0 EA–LH

Hhft2 349 103,089 572±75 175±41 19±14 EH

Hpl3 366 121,447 519±65 165±37 33±17 EH

Npld 80 24,210 1,070±211 413±131 123±72 LN–MN

Nm 74 35,101 826±153 285±90 86±49 LN–MN

1Unit AHvt includes vallis floor material (AHv) and irregular vallis floor material (AHvi). 

2Unit Hhft includes Hadriaca Patera upper (Hhfu) and lower flank (Hhfl) materials.

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Available at http://pubs.usgs.gov/sim/2007/2936

Printed on recycled paper

1Planetary Science Institute, Tucson, AZ

2School of Earth and Space Exploration, Arizona State University,

 Tempe, AZ

MC–21

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