Astronomy

Mars is only about one-half the size of Earth and yet has several volcanoes that surpass the scale of the largest terrestrial volcanoes. The most massive volcanoes are located on huge uplifts or domes in the Tharsis and Elysium regions of Mars. The Tharsis dome is 4,000 kilometers across and rises to 10 kilometers in height. Located on its northwest flank are three large shield volcanoes: Ascraeus Mons, Pavonis Mons and Arsia Mons. Beyond the dome’s northwest edge is Olympus Mons, the largest of the Tharsis volcanoes. Olympus Mons is classified as a shield volcano. It is 24 kilometers high, 550 kilometers in diameter and is rimmed by a 6 kilometers high scarp. It is one of the largest volcanoes in the Solar System. By comparison the largest volcano on Earth is Mauna Loa which is 9 kilometers high and 120 kilometers across.

Elysium Planitia is the second largest volcanic region on Mars. Elysium Planitia is centered on a broad dome that is 1,700 by 2,400 kilometers in size. It has smaller volcanoes than the Tharsis region, but a more diverse volcanic history. The three volcanoes include Hecates Tholus, Elysium Mons and Albor Tholus.

The large shield volcanoes on Mars resemble Hawaiian shield volcanoes. They both have effusive eruptions which are relatively quiet and basaltic in nature. Both have summit pits or calderas and long lava flows or channels. The biggest difference between Martian and Terrestrial volcanoes is size. The volcanoes in the Tharsis region are 10 to 100 times larger than those on Earth. They were built from large magma chambers deep within the Martian crust. The Martian flows are also much longer. This is probably due to larger eruption rates and to lower gravity. One of the reasons volcanoes of such magnitude were able to form on Mars is because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years. On Earth, the tectonic flow of the crust across the hot volcanic regions prevent large volcanoes from forming. The Hawaiian islands were created as the Pacific plate moved northwest. These volcanoes have a relatively short life time. As the plate moves new volcanoes form and the old ones become silent.

Not all Martian volcanoes are classified as shields with effusive eruption styles. North of the Tharsis region lies Alba Patera. This volcano is comparable to Olympus Mons in its horizontal extent but not in height. Its base diameter is 1,500 kilometers but is less than 7 kilometers high. Ceraunius Tholus is one of the smaller volcanoes. It is about the size of the Big Island of Hawaii. It exhibits explosive eruption characteristics and probably consists of ash deposits. Tyrrhena Patera and Hadriaca Patera both have deeply eroded features which indicate explosive ash eruptions. Mt. Saint Helens is an example of a terrestrial ash eruption.

Views of Martian Volcanoes

This set of images was chosen to show some of the best examples of volcanic landforms on Mars.

Tharsis Montes

The alignment of the three shield volcanoes that make up the Tharsis [THAR-siss] Montes region is clearly evident in this view. They are named Ascraeus Mons (top right), Pavonis Mons (middle) and Arsia Mons (bottom). Olympus Mons can be seen in the upper left hand corner. The three volcanoes are each somewhat smaller than Olympus Mons, varying from 350 to 450 kilometers in horizontal extent and each rising about 15 kilometers above the surrounding plains. The Tharsis Montes are located on the crest of a broad uplift of the Martian crust so that their summits are at about the same elevation as the summit of Olympus Mons. The fractures southeast of Pavonis Mons are named Noctis Labyrinthus; this region merges with the enormous Vallis Marineris canyon system to the east.

Mantle Convection

This image shows a computer simulation of processes in the interior of Mars that could have produced the Tharsis region. The color differences are variations in temperature. Hot regions are red and cold regions are blue and green, with the difference between the hot and cold regions being as much as 1000°C. Because of thermal expansion, hot rock has a lower density than cold rock. These differences in density cause the hot material to rise toward the surface and the cold material to sink into the interior, creating a large-scale circulation known as mantle convection. This type of mantle flow produces plate tectonics on Earth. The hot, rising material tends to push the surface of the planet up, and the cold, sinking material tends to pull the surface down. These motions contribute to the overall topography of the planet. This deformation of the planet’s surface is shown in gray along the outer surface of the planet in this image. The amount of deformation is highly exaggerated to make it visible here. The actual uplift in Tharsis is estimated to be about 8 kilometers at its center. This uplift also stretches the crust, forming features such as grabens and Valles Marineris. In addition, the hot, rising material may melt as it approaches the surface, producing volcanic activity.

Elysium Planitia

Elysium Planitia is the second largest volcanic region on Mars. It is located on a broad dome that is 1,700 by 2,400 kilometers in size. The volcanoes Hecates Tholus, Elysium Mons and Albor Tholus can be seen going from north to south (top to bottom) in this image. Hectas Tholus is 160 by 175 kilometers in size with a caldera complex 11.3 by 9.1 kilometers in size. Elysium Mons is the largest volcano in this region. It has base dimensions of 420 by 500 by 700 kilometers and rises 13 kilometers above the surrounding plains. Its summit caldera is about 14.1 kilometers in diameter. Albor Tholus measures 160 by 150 kilometers with a summit caldera of 35 by 30 kilometers. Its northwest flanks have been partially buried by lava flows from Elysium Mons.

Olympus Mons

Olympus [oh-LIM-pus] Mons is the largest volcano known in the solar system. It is classified as a shield volcano, similar to volcanoes in Hawaii. The central edifice of Olympus Mons has a summit caldera 24 kilometers above the surrounding plains. Surrounding the volcano is an outward-facing scarp 550 kilometers in diameter and several kilometers high. Beyond the scarp is a moat filled with lava, most likely derived from Olympus Mons. Farther out is an aureole of characteristically grooved terrain, just visible at the top of the frame.

3D Olympus Mons

This 3D image of Olympus Mons was created from several images taken from different spacecraft positions and combined with a computer model of the surface topography. The final mosaic shows Olympus as it would be seen from the northeast. It is possible that volcanoes of such magnitude were able to form on Mars because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years.

Ascraeus Mons Summit

This complex caldera is composed of several discrete centers of collapse where the older collapse features are cross-cut by more recent collapse events. The lowermost circular floor preserves the last lava flooding event that followed the last major collapse. The southern wall of the caldera has at least 3 kilometers of vertical relief with an average slope of at least 26° (from horizontal). The caldera complex truncates several lava flows, indicating that the flows predate the collapse event and that their source areas have been destroyed by the caldera formation.

Arsia Mons

The caldera on Arsia Mons is considerably larger than the calderas on either Ascraeus Mons or Pavonis Mons. However, the last major collapse event on Arsia Mons was followed by a substantial outpouring of lava within the caldera. The caldera rim has been breached on the southwest side while the caldera floor lavas bury portions of the northeast rim. Aligned between these breaks in the caldera is a series of very subdued domes on the caldera floor, perhaps representing localized sources of the lava that flooded the caldera. The flaks of the shield have been deeply eroded near the locations of the breaks in the caldera rim and lava flows extend away from the volcanoes at these embayments.

Apollinaris Patera

This view of Apollinaris Patera, shows characteristics of an explosive origin and an effusive origin. Incised valleys in most of the flanks of Apollinaris Patera indicates ash deposits and an explosive origin. On the west side (left), landslides that have shaped its surface also indicate ash deposits. Towards the south flank, a large fan of material flowed out of the volcano. This indicates an effusive origin. Perhaps during its early development Apollinaris Patera had an explosive origin with effusive eruptions taking place later on.

Ceraunius Tholus and Uranius Tholus

Ceraunius Tholus (bottom) shows several incised valleys cut into its flanks which indicate that it was easily eroded and probably consists of ash deposits due to explosive activity. The lower flanks of the volcano have been buried beneath the plains material. Ceraunius Tholus is about the size of the Big Island of Hawaii. Uranius Tholus (Top) also shows similar characteristics to Ceraunius Tholus. A major impact crater, just above Ceranius Tholus, postdates the plains material and volcano. However, a prominent delta of probable volcanic material was emplaced within the impact crater at the mouth of a sinuous channel that extends up the flank of Cerauius Tholous to the summit crater. (Credit: Calvin J. Hamilton and Lunar and Planetary Institute)

Ceraunius Tholus and Uranius Tholus - 3D

This is a three dimensional view of Ceraunius Tholus (right) and Uranius Tholus (left). The view is from the northwest.

Tharsis Tholus

Tharsis Tholus measures about 150 kilometers across and 8 kilometers high. The east and west flanks are indented giving it a strange appearance. One possible cause for its appearance is that when the lava supply drained away, the center of the volcano collapsed. An alternative is that big slump areas carried off portions of the flanks, giving it the broken appearance.

Uranius Patera

Uranius Patera is about the size of the Big Island of Hawaii. It is about 3 kilometers in height. It has shallow slopes and lava flows. This indicates an effusive origin. The center caldera was formed when lava drained away and the volcano collapsed.

Ulysses Patera

This feature is an example of a class of volcanoes that are considerably smaller than the broad shield volcanoes. The summit consists of a single, very circular caldera with a smooth floor that predates the ejecta from two large impact craters. The lower flanks of the volcano, including portions of the impact craters, have been buried by the material that makes up the surrounding plains. This superpositional relationship indicates that the plains were emplaced subsequent to both the volcano and the large impact craters on the volcano. The plains are probably made up of lava supplied from Tharsis Montes that flowed down the sides of the broad uplift associated with the Tharsis shields. Both the plains and the volcano are cut by a graben, indicating tectonic activity subsequent to the emplacement of the plains.

Ulysses Patera in 3D

This shows perspective view of Ulysses Patera looking from the north.

Tyrrhena Patera

Volcanoes located within the densely cratered southern highlands have a very different morphology from either the Tharsis or Elysium volcanoes. Tyrrhena Patera has very little vertical relief (< 2 kilometers), resulting in very shallow flank slopes. The flanks of the volcano are deeply eroded with many broad channels that radiate from the summit region. The low relief and easily erodible nature of the flank materials has been interpreted to indicate that the bulk of the volcano is composed of pyroclastic ash deposits. This interpretation implies that the style of eruption for the highland volcanoes like Tyrrhena Patera is significantly different from the repeated effusion of fluid lavas that built up the shield volcanoes.

Tyrrhena Patera in 3D

This shows perspective view of Tyrrhena Patera looking from the north. The vertical dimension has been greatly exaggerated to show detail.

Hadriaca Patera

Much like Tyrrhena Patera, Hadriaca Patera is a deeply eroded feature having little vertical relief. Several impact craters are superimposed on the eroded flanks, indicating a great age for this volcano. A large channel has its source near the southeastern margin of the volcano; the fluid that carved the channel flowed southwest into the interior of the Hellas basin.

Tempe Volcano

Volcanic construct on Mars are not all enormous mountains like the Tharsis Montes. This elongate hill surmounted by a linear depression is interpreted to be a product of localized but not extremely voluminous eruptions. If the volcanic material was emplaced by ejection along a ballistic trajectory, this feature may be similar to a terrestrial cinder cone. This feature is aligned with several grabens in the area so that a structural weakness in the crust may have provided the conduit for the volcanic material to reach the surface.

Hellas Mounds

Numerous small mounds having summit craters are found in various locations on Mars. The mounds shown here are east of the Hellas basin. These features have been interpreted to be pseudocraters created by localized phreatic explosions where lava interacts with volatile-rich ground. Most of the mounds are between 400 meters to 1 kilometer across. Many have slotlike summit vents. However, images presently available do not have sufficient resolution to show conclusive evidence of a volcanic origin for the mounds.