There are many vulcanic mountains on Mars.

Not so very long ago our knowledge of Mars was supplied by using the humble telescope.  Whenever the Earth and Mars fell into close alignment astronomers diligently mapped the surface.  The Mars Global Surveyor project, launched in 1996 and completed in 2006, has revolutionised our understanding of the planet. It generated some extremely detailed maps of the planet.

The following maps from the project show the basic geography of Mars.  The maps are colour coded to show elevation above  a reference level.  The difference between the hemispheres is striking.  The northern hemisphere shown in blue is flat with few impact craters caused by asteroids. The southern hemisphere is mountainous and shows much higher relief.  The interpretation of these differences is puzzling planetary scientists to this day. One view is that there might have been a substantial ocean in the Northern hemisphere.

Source: Wikipedia Topographic map of Mars, courtesy NASA Goddard Space Flight Center, from Mars Global Surveyor laser altimeter research

The most mountainous area of Mars which shows up in red straddles the equator.  This area is known as the Tharsis Bulge and is home to some of the largest volcanoes in the solar system.  Three very large volcanoes can be seen on the bulge.Olympus Mons lies on the edge of the bulge at approximately 18°N 133°W. 

Source: Wikipedia

The shear scale of Olympus Mons is extra-ordinary.  This edifice rises 27 kilometers (16.7 miles, or 88,600 ft) from the mean surface level.  This is three times the height of Mount Everest.  The volcano resembles a giant pancake.  It spreads out over 550 km (342 miles) and has a gentle incline of just 2%.  The perimeter is lined by steep cliffs that are up to 6 kilometers (4 miles) high.  The central caldera complex is 85 km (53 km) long, 60 km (37 miles) wide, and up to 3 km deep and contains six overlapping pit craters.  The volcano is not entirely symmetric. The peak is so high that it rises above the Martian dust storms and can be seen by telescope from Earth.

Geologists define Olympus Mons as a shield volcano. Volcanoes of a similar type are found in the Hawaiian Islands.  The slope gradually builds up when highly fluid lava effluxes over a long period of time. Two features result in a much higher volcano on Mars.  Mars has a lower gravity than on Earth which allows a larger mound to build up.  Secondly, there are no plate tectonics on Mars.  Volcanoes, such as Olympus Mons, have built up their considerable bulk because they have sat above “hot stops” for a considerable period. The caldera was formed after the volcano ceased to be active.  It was formed by a collapse of the roof of an empty magma chamber. The satellite pictures imply there might have been several collapses.

Overflights by the Mars Express orbiter suggest that western flank of Olympus Mons was formed between 115 million and 2 million years ago.  This is comparatively recent in geological terms and suggests that the volcano may still be active.

There are many mysteries associated with the volcano.

The shallow slope and asymmetric shape of the volcano require explanation.  In February 2009 two professors, Patrick McGovern and Julia Morgan from Rice University published an article in Geology magazine.  Their view is that the volcano has developed on top of clay sediments.  More excitingly, these sediments may contain water within a sheltered environment that might support life. 

No one understands the formation of the very large cliffs at the base of the volcano. 

The origin of the Tharsis Bulge is a enigmatic.  The map compiled from the Mars Global Surveyor project shows a very long canyon extending from the Tharsis Bulge.  This is the Valles Marineris.  It is 4000 km (2,5000 miles) long. This tear is believed to have formed to accommodate the sustained uplift of rock within the Bulge.

On the map notice an area of low lying land in the southern hemisphere.  This basin is almost diametrically opposite the Tharsis Bulge.  One theory put forward in 2008 believes this is the site of a massive meteor impact.  Shock waves passing out from the event might be responsible for an upwelling of magma and the onset of volcanic activity within the Bulge. 

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