Supervolcanoes on Mars!

The process that created the crater-rich region of Mars known as Arabia Terra has been determined – and they are not even craters at all!   They are calderas formed from collapsed volcanoes, containing large deposits of volcanic rock and ash debris.  The volcanic field, located in the equatorial region of the planet, consist of dozens of crater-like features, whose largest measures about 35 miles long and 55 miles wide (that’s bigger than Rhode Island).

Scientists associated with NASA and the Planetary Science Institute have used a variety of techniques to analyze the surficial geology from multiple Martian spacecraft. The Mars Express satellite used lasers to produce topographic maps and thermal images while high-resolution photographs were taken by the Mars Reconnaissance Orbiter and Mars Global Surveyor.  The science team determined that only ancient supervolcanoes could produce the vast quantities of volcanic rocks and ash debris found in the area.  The so-called ‘plain-style caldera complexes,’ similar to the Yellowstone caldera and Snake River Plain on Earth, are characterized by collapsed, low craters and plain-like lava flows.  The calderas themselves feature rings of fault scarps caused by the collapse of the structure as it sinks into the now-empty magma chamber; the structures are identical to structures found in collapsed calderas on earth, such as in Yellowstone and Long Valley, CA. During some eruptions, the empty magma chamber left behind acts like a giant sinkhole, collapsing under its own weight; it’s similar to trying to stand on an empty cardboard box versus a full one. These supervolcanoes represent a new form of Martian volcanism not previously identified anywhere else on the planet.

False color map of Martian topography. Cool colors indicate low elevations, while warm colors indicate high elevations. Arabia Terra, indicated by the box near the middle of the image, is home to Mars' newly identified supervolcanoes. Image modified from NASA.

Mars is no stranger to volcanism.  It is most known for its shield volcanoes like Olympus Mons, the largest volcano in the solar system, located in the Tharsis province.  These large volcanoes are similar in morphology to the volcanoes found in Hawaii, with gentle slopes that spread over hundreds of miles. Also like Hawaii, they would have erupted effusively, not producing the ash columns like those at Mt. St. Helens.  These eruptions were caused by magma chambers deep beneath the planet’s surface and occurred over long periods of time. 

In contrast, the newly identified Martian supervolcanoes would have had magma chambers closer to the surface and erupted explosively from several vents.  Supervolcanoes erupt massive amounts of material;  on Earth, a volcano must eject at least 1000 km³ of volcanic material (the equivalent to 400 Olympic swimming pools) to be considered a supervolcano.  There are dozens of known explosive supereruptions on Earth during the course of geologic time, the largest being the La Garita Caldera eruption in Colorado, which erupted 5,000 km³ of material.  Calculations based on satellite data indicate that the craters at Arabia Terra erupted almost twice as much material as the La Garita Caldera and thousands times more material than other Martian volcanoes.

The question remains: Why would supervolcanoes erupt at Arabia Terra and not anywhere else on the planet?  The Arabia Terra caldera is one of the oldest known features on the planet.  To the north of the region are fields of younger shield volcanoes; to the south are fields of crater impacts from meteorites that have decimated the landscape.  As such, the Arabia Terra region is one of the few regions of Mars where such features would be preserved and not destroyed or covered by other rocks. The early Martian surface may have been covered by these large supervolcanoes in the past, with only those at Arabia Terra still apparent.  Additionally, volatiles often need to be added to the magma to produce large supereruptions – volatiles like water! These supervolcanoes could be an indicator of higher water content on Mars billions of years ago. 

The discovery of supervolcanoes on Mars is an exciting discovery for not only planetary geologists but for terrestrial volcanologists as well.  Further study of these large eruption deposits could give some insight to the conditions surrounding the supereruptions on Earth, like those from Yellowstone.

Check out the original paper at: Michalski, J.R., and Bleacher, J.E. (2013).  “Supervolcanoes within an achient volcanic province in Arabia Terra, Mars,” Nature 502 pg 47-52