Why does mars have such large volcanoes

Although Mars may have been tectonically active in its early history, there is no evidence of geologically recent horizontal motion similar to plate tectonic motion on earth. Volcanism on Mars may be partly derived from the melting of hot mantle plumes. The lack of lateral motion means that these mantle hotspots would remain fixed relative to the Martian surface. This mechanism may account for regional uplift and volcanism at several sites on the Tharsis bulge , the extensive light-colored region on the west side of the image shown here.

The Tharsis bulge is associated with a number of exceptionally large volcanoes, which show as dark red spots on the western side of the image. The enormous Valles Marineris canyon system is visible in the center of the image, east of the Tharsis bulge.

This huge feature contains numerous canyons, with depths from 2 to 7 km, exposed over a distance of km for a close-up view, double-click Valles Marineris. The Marineris canyons were not eroded by running water, but rather by stretching and cracking of the crust during mantle-plume uplift of the Tharsis bulge. However, there is clear evidence of ancient water erosion on Mars, which may date back to nearly 4 billion years ago. There have been 23 scientific missions to Mars, which include Martian flybys, orbiters, and unmanned landings.

The first spacecraft to land on Mars was Mariner 4 in , followed by Viking 1 in and Mars Pathfinder in The volcanic features on Mars are very similar in shape, but not in scale, to those found on earth, and they probably formed by similar processes. The most recent lava flows that formed Olympus Mons spill over the steep scarp that surrounds its base. This scarp likely formed when parts of the volcano's flank collapsed and slid away.

Mars Volcanoes Mars today has no active volcanoes. A perspective view of part of the large scarp that surrounds the base of Olympus Mons. The explosions happen because as magma rises near the surface, the pressure keeping the water and gases dissolved goes away. Lowered pressure causes the gases to form bubbles in the magma. If enough gas is dissolved in the magma, this can cause a runaway effect. At that point, the superheated water vapor and gases burst out of the lava like popping the top of a soda can after shaking it.

The eruption of Mount St. Helens occurred in this way, after an earthquake shook off the volcano's upper part and exposed gas-rich magma. Most Earth volcanism is basaltic. Basalt bah-SALT is an igneous rock rich in iron and magnesium minerals. It is usually dark gray or black. The most iron-rich basalts erupt at high temperatures and flow easily, like maple syrup. When magma has more silica in its composition, however, it moves stiffly, like cookie dough or peanut butter.

Being thicker and stickier, high-silica magmas make it difficult for gas bubbles to escape smoothly once they form. Again, this makes explosive eruptions more likely. Volcanic eruptions on Mars have built numerous kinds of features. The main types of features are what scientists call shield volcanoes and flood basalts. Although it has taken billions of years to form, some regions of the mountain may be only a few million years old, relatively young in the lifetime of the solar system.

As such, Olympus Mons may still be an active volcano with the potential to erupt. The tallest volcano in the solar system may also house rock glaciers — rocky debris frozen in ice.

Snow and ice deposits above the base of the shield could result in such glaciers. Water-ice insulated by surface dust may exist near the top of the volcano.

The tops of these glaciers may host ridges, furrows, and lobes, and be covered by rocks and boulders, and could be as young as four million years old. Why would such a huge volcano form on Mars but not on Earth? Scientists think that the lower surface gravity of the red planet, combined with higher eruption rates, allowed for the lava on Mars to pile up higher. The presence and absence of tectonic plates could also play an important role in the different kinds of volcanoes.

The hot spots of lava under the crust remain in the same location on both planets. On Earth, however, the movement of the crust prevents the steady buildup of lava.

The Hawaiian Islands , for instance, formed as a plate drifted over a hot spot. Each eruption created a small island in a different spot.