page_title: Volcanism on Mars
section_title: Tharsis volcanic province
hierarchical_section_title: Volcanism on Mars / Tharsis volcanic province
caption_attribution_description: English: Mars Orbiter Laser Altimeter (MOLA) colorized topographic map of the western hemisphere of Mars, showing the Tharsis and Valles Marineris regions. The impact basin Argyre is at lower right. Many of the features on this map are annotated in Wikimedia Commons.
context_page_description: Volcanic activity, or volcanism, has played a significant role in the geologic evolution of Mars. Scientists have known since the Mariner 9 mission in 1972 that volcanic features cover large portions of the Martian surface. These features include extensive lava flows, vast lava plains, and the largest known volcanoes in the Solar System. Martian volcanic features range in age from Noachian to late Amazonian, indicating that the planet has been volcanically active throughout its history, and some speculate it probably still is so today. Both Earth and Mars are large, differentiated planets built from similar chondritic materials. Many of the same magmatic processes that occur on Earth also occurred on Mars, and both planets are similar enough compositionally that the same names can be applied to their igneous rocks and minerals.
  Volcanism is a process in which magma from a planet's interior rises through the crust and erupts on the surface. The erupted materials consist of molten rock, hot fragmental debris, and gases. Volcanism is a principal way that planets release their internal heat.
context_section_description: The western hemisphere of Mars is dominated by a massive volcano-tectonic complex known as the Tharsis region or the Tharsis bulge. This immense, elevated structure is thousands of kilometers in diameter and covers up to 25% of the planet's surface. Averaging 7–10 km above datum (Martian "sea" level), Tharsis contains the highest elevations on the planet. Three enormous volcanoes, Ascraeus Mons, Pavonis Mons, and Arsia Mons (collectively known as the Tharsis Montes), sit aligned northeast–southwest along the crest of the bulge. The vast Alba Mons (formerly Alba Patera) occupies the northern part of the region. The huge shield volcano Olympus Mons lies off the main bulge, at the western edge of the province.
  Built up by countless generations of lava flows and ash, the Tharsis bulge contains some of the youngest lava flows on Mars, but the bulge itself is believed to be very ancient. Geologic evidence indicates that most of the mass of Tharsis was in place by the end of the Noachian Period, about 3.7 billion years ago (Gya). Tharsis is so massive that it has placed tremendous stresses on the planet's lithosphere, generating immense extensional fractures (grabens and rift valleys) that extend halfway around the planet. The mass of Tharsis could have even altered the orientation of Mars' rotational axis, causing climate changes.
caption: MOLA colorized shaded-relief map of western hemisphere of Mars showing Tharsis bulge (shades of red and brown). Tall volcanoes appear white.
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