The Tale of the Martian Tsunamis

Pictures of Mars - Liquid Water on Mars
Mars may be dry now, but its surface shows evidence of water that carved out gullies and flooded across the plains. Copyright 1995-2003, California Institute of Technology

Giant Waves on Mars

Imagine this: a calm and placid day on ancient Mars. The oceans twinkle in the sunlight as waves gently wash to shore. Suddenly, bolides from an incoming chunk of asteroid come ripping through the sky. Some of the pieces fall into the ocean, sending giant waves — tsunamis — crashing to shore. In a few minutes, these 120-foot-tall waves moved hundreds of kilometers inland, scouring out whatever lay in their path.

This scenario is not so far-fetched; we know Earth has been hit many times in the past, and such tsunamis also resulted. They also occur when earthquakes happen, as we saw with the magnitude 6.6 earthquake that hit Japan in April 2011 and did damage to the Fukushima reactors. So, it's not too hard to imagine the bombardment of Mars, particularly since impact craters are scattered across its surface. It's tougher to imagine Mars with watery oceans, since the Mars we see today is a dry, cold, dusty desert. Yet, knowing the story of water on Mars is a huge part of understanding the planet itself.

Search Out the Shorelines

For tsunamis on early Mars, the Red Planet had to have deep oceans in the past. This is a much-debated point in the planetary science community. Oceans usually leave evidence behind, such as shorelines. On Earth, shorelines can disappear over geologic time. However, if you dig down deep enough (or take core samples using special drilling equipment), you can find the layers of sand and rocks deposited along shorelines. Also, you can often see traces of ancient oceans in mountain rocks. For example, in the Rocky Mountains, which was once an ancient ocean, you can find evidence in the layers of rock that now stick up as part of the mountains. 

On Mars, finding ocean shorelines is more difficult because we really only have images to study. And, even if something looks like an ocean shoreline, it's open to interpretation, since lakes can also make shorelines, as can rivers. So, the debate is over what caused them. An ocean shoreline on Mars (as on Earth) needs to run along a fairly long stretch of landscape maintaining the same elevation. Since those are few and far between on Mars, it may indicate that ancient oceans didn't occur on Mars. However, absence of proof is not proof of absence. Ancient shorelines may be covered up or changed from their original layout.

Tsunamis Effect Shorelines

Astronomers studying the effects of impacts have come up with the idea that tsunamis triggered by ancient impacts on Mars could have washed up huge deposits of rock and sand that would have deformed and covered up the shorelines of the oceans in many places. To test this, scientists did geologic mapping of the Martian northern plains and found huge deposits of sediments that were very like put there by the effects of impacts in an ancient ocean. The work was done at the Planetary Science Institute, and also show that between impacts, the oceans returned to their previous heights. This left behind huge piles of boulders, as well as flow channels where the water moved back into the ocean basin.

At the same time, Mars's climate became much colder. When the next mega-tsunami occurred, the water left behind in the flow channels froze, along with the rocks and sand they carried along with them during the flooding. Eventually, Mars lost all its water — either to space or to frozen deposits underground — leaving behind the oddly shaped lobes and devastated shorelines that planetary scientists are currently discussing as evidence for (or against) the idea of ancient oceans. Understanding the story of how Mars changed is ALSO a huge part of understanding the Red Planet as it is today.

Future Studies

Obviously, the best way to find out when and if an ancient ocean existed on Mars is to actually GO there and study the landscapes and rocks in person. As on Earth, this gives you first-hand experience with the geology of a region. Images will show explorers where to go (such as the Martian northern plains.  There are likely other places around the planet with similar deposits of rocks that could help them understand the action of water, particularly tsunami waves. 

Since the first human missions to Mars are still years away and we're still figuring out what it will be like to actually live there, the best way to understand what's seen in Mars images is to find places on Earth that mimic the landscapes on Mars. The high mountains of Tibet are a good spot, as are the deserts of the American west, and the northern plains of Canada. These all over extreme environmental conditions similar (but not exactly like) those on Mars of the past and present, and should give scientists a better idea of what to look for once the first humans DO set foot on the Red Planet.