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Roger Weller, geology instructor

wellerr@cochise.edu

Mars-Tharsis
by Nicolas P.
Physical Geology
Fall 2016
  
 
 

Tharsis Plateau
 

I have had a fascination on and off with Marís volcanos for quite a few years. I always found documentaries of people climbing, and dying in the Himalayas to be fascinating because of how they change human morals, and perspective. Friends left each other for dead, and people summited ahead of storms knowing the risk they were taking, may cost them their lives. With these stories of human misery, triumph, and often idiocy in mind, I always found it captivating that there were mountains that doubled the height of The Himalayasí Mount Everest on Mars.           


The Tharsis Plateau is an enormous volcanic plateau on the planet of Mars. It is located in the western hemisphere of Mars. The plateau is home to the largest mountain in the solar system, Olympus Mons, as well as three other incredibly large shield volcanoes named Ascraeus Mons, Arsia Mons, and Pavonis Mons.










 

 

 

The standard view is that the Tharis Plateau shield volcanos occur over a hotspot like many shield volcanos do on Earth. A hot spot is a region under a planetís surface that produces basaltic magma in huge supplies. The Hawaiian Islands are an example of this phenomena, but the shield volcanoes on the Tharsis Plateau dwarf anything seen on Earth or in the known solar system. The plateau itself is the largest topographic feature on the planet and dominates the western hemisphere. The bulge that makes up the plateau is 5,000km (3107mi) across, and depending on how it is defined, covers up to 25% of Marsí surface area. The entire region is a product of volcanic and tectonic processes which have caused extreme crustal deformation. It is so large that it likely caused true polar wander (a change in the geographical location of the north and south poles on a planet caused by a solid body rotation), due to changing the way Mars rotates on its axis over time.
 

There is debate as to whether crustal buoyancy is what caused the bulge, or if the entire region is a large mass of igneous material supported by the underlying lithosphere. Analysis of gravitational data and the patterns of faults on the plateau suggest that it is likely one large mass of igneous material. The following image is the global topography of Mars. The area in red on the left-hand side is the Tharsis Bulge, which is mind bogglingly immense considering you are looking at the entire surface of Mars:


 

The volcanoes in the Tharsis Plateau region are shield volcanoes. Letís talk a little bit about what shield volcanoes are before diving into why these ones are so big. Shield volcanoes are the largest volcanoes on earth. Their profile is that of a Roman shield laid flat on the Earthís surface. They are made almost entirely of basaltic lava, which is very fluid. They are among the least violent volcanoes because they do not build up tremendous pressure before erupting. The lava spreads very thin when erupted, giving them their quite gradual profile. Essentially, the entire volcano is made of repeated layers of cooled lava, spreading out in all directions from many past eruptions.

 

 

Olympus Mons is especially immense among shield volcanos, and therefore garners the most attention publicly. Its footprint is nearly the size of France, approximately the same size as Arizona, and dwarves both Mount Everest and Mauna Kea. It is a staggering 21,229m (69,660ft) in height. Its slope is very gradual, like other shield volcanoes.

 


 

 


 

 

So why is Olympus Mons so big? Nasaís website has a few possible explanations, including higher eruption rates than those on earth and lower surface gravity. Also, Marsí crust is either much more stationary than Earthís, or frozen in place entirely, allowing a much larger volcano to build up above the hotspot. Whereas, Earthís crust moves, leaving trails of volcanoes like the Hawaiian Islands. If one is to look at the trail of Hawaiian Islands, you can see that although the hotspot under the surface remains stationary, the plate above it moves. This also will allow the seamount of LŲ'ihi to eventually breech the surface of the Pacific Ocean to form a new Hawaiian Island. Olympus Mons does not appear to be on a plate that is moving at all, and therefore lava continues to spew out of the ground in the same place for millions of years.
 


 

Olympus Monís has a grouping of craters and lava flows of many different ages, due to its perpetually active nature. High resolution photographs indicate that on its northwestern face the lava flows vary in age from 115 to 2 million years old. It has six overlapping calderas, the largest and oldest appears to have formed as a single colossal lava lake:
 

 

Olympus Mons also has signs of titanic landslides the scope of which is hard to wrap your mind around:
 


 

Considering the volcano, you are looking at is the size of Arizona, one can imagine
the size of the landslide that is seen in the foreground of the picture.
 

            Although Olympus Mons is the most popular and easiest of the volcanoes on Mars to find information on, there are several others that need mentioning, including Arsia Mons. This shield volcano is the furthest south in the collection of three volcanos known as Tharsis Montes. It is the second largest known volcano in the solar system, and is 30 times the volume of Mauna Loa in Hawaii (which is the largest volcano on Earth). It has been proposed that due to these three volcanoes forming a straight line, they could be the result of plate tectonics like chains of volcanos formed from hot spots on Earth. If not for figuratively standing in Olympus Monsí shadow, this volcano would captivate minds with its size and character, as would the other two volcanos that along with Arsia Mons form the Tharsis Montes volcanos:
 


 

            Ascraeus Mons is the northern most, and tallest, of this titanic trio of shield volcanos. This volcano was discovered by the Mariner 9 Spacecraft in 1971. It was called the North Spot because it was the northernmost of four visible spots that could be seen standing above a global dust storm. This can give one an idea of the scope we are dealing with here. Even Marsí famous planetary dust storms fall below the shoulders of these giants. As with the other volcanos of the area, it is also a shield volcano and formed over thousands, or millions of years due to fluid basaltic lava flows.
 

            Lastly is the central volcano in the chain Pavonis Mons. Also, discovered during the planetwide dust storm in 1971, and originally called Middle Spot. Its peak is 46,000ft in height. It is the smallest volcano of the three-volcano chain, but is still beyond 7000ft taller than the largest volcano on Earth. Any of these volcanos, if found on their own, would be infamous for their magnitude and an attraction for school children and adults alike.
 

I find the discovery, and exploration of the solar system to be incredible. I hope we continue to explore our universe, so that we can further expand the horizon of human imagination and knowledge. I think that there is more enchantment within our universe than we often find in our day to day, pedestrian lives. If scientific exploration continues to grow in this area as we move forward into the future, it will continue to test our imaginations and teach us more about the inspiration that life should offer.


 

 

Sources

Arsia Mons. (n.d.). Retrieved November 29, 2016, from https://en.wikipedia.org/wiki/Arsia_Mons

Ascraeus Mons. (n.d.). Retrieved November 29, 2016, from https://en.wikipedia.org/wiki/Ascraeus_Mons

Loihi Seamount: The Next Volcanic Island in the Hawaiian Chain. (n.d.). Retrieved November 29, 2016, from http://geology.com/usgs/loihi-seamount/

OLYMPUS MONS. (n.d.). Retrieved November 29, 2016, from https://mars.jpl.nasa.gov/gallery/atlas/olympus-mons.html

Pavonis Mons. (n.d.). Retrieved November 29, 2016, from https://en.wikipedia.org/wiki/Pavonis_Mons

Plate Tectonics and the Hawaiian Hot Spot. (n.d.). Retrieved November 29, 2016, from http://geology.com/usgs/hawaiian-hot-spot/

Society, N. G. (2012). Volcanoes. Retrieved November 30, 2016, from http://nationalgeographic.org/media/volcano-satellite-images/

Tharsis. (n.d.). Retrieved November 29, 2016, from https://en.wikipedia.org/wiki/Tharsis

Volcano World. (n.d.). Retrieved November 29, 2016, from http://volcano.oregonstate.edu/shield-volcanoes