Discovery supports ancient ocean theory and could lead to clues about past life on the red planet.
In a paper published in Nature, an international team of researchers outline evidence that Mars experienced two mega-tsunamis millions of years ago. The lack of shoreline features on Mars has long puzzled scientists who hypothesized that the northern lowlands of the planet were once covered by an ocean. The tsunami deposits offer an explanation and provide definitive evidence that an early ocean existed. We spoke with the paper’s lead author, Alexis Rodriguez of the Planetary Science Institute, who explains the findings and their implications.
ResearchGate: How can you tell that these tsunamis happened?
Rodriguez: They left a sedimentary record consisting of vast rocky lobate deposits (locally eroded by backwash channels) for the older tsunami, and ice-rich lobes for the younger tsunami. The lobes are oriented upslope, so they had to have formed by run-up flows capable of transporting large boulders and water over tens to hundreds of kilometers. Tsunamis are the most, if not the only, fitting explanation for these observations.
RG: How does your discovery change what we know about Mars’s oceans?
Rodriguez: For a start, it reconciles the ocean hypothesis itself with the puzzling absence of shorelines distributed along a constant elevation. This is because the tsunamis would have overridden and buried the shorelines, and their margins of course do not follow a constant elevation. Tsunamis move far inland and can deposit materials over hills and valleys, covering a vast range of topography. Then, of course, there is the fact that the discovery of tsunami deposits represents definite evidence for the existence of the early Mars ocean.
RG: How big were the tsunamis?
Rodriguez: We have estimated that on average they were about 50 meters high, but at some locations they could have reached as much as 120 m. Basically, high-rise heights. The surface areas they covered within the study region are also enormous; the older tsunami with ~800,000 Km^2, and he younger with 1000,000 Km^2. So, each had roughly the combined areas of California, Nevada and Oregon.
RG: When did they happen? What caused them?
Rodriguez: They happened approximately 3,400 million years ago, and they were likely separated by 3 to 15 million years.
We find that meteor impacts capable of generating craters 30 km in diameter are a likely cause, based on how frequently they occur over the northern ocean. However, there are other processes capable of triggering tsunamis such as quakes or landslides, and we do no not rule those out.
RG: Apart from the timeframe, are there other differences between the two events?
Rodriguez: The second tsunami appears to have frozen up prior to entering the backwash phase. We think this is because the wave propagated under much colder climatic conditions than those under which the first tsunami wave took place. These type of ice-rich slurry flows are rarely observed on Earth, however this video shows an example of what the younger tsunami might have looked like as it propagated. What is shown in the video is not a tsunami, but the surge flow is a good analog as far as the process goes.
RG: Could this discovery have any implications for the search for life on Mars?
Rodriguez: Yes. Particularly the second tsunami lobes, which are made of water-ice that emanated from the ocean itself. Sampling these materials for prebiotic and biotic signatures is important from an astrobiological perspective. Also, determining the composition of the ocean will be helpful to assess its habitability potential.
RG: What will the next research steps be for you?
Rodriguez: We are looking at marine lakes produced where the tsunamis spilled over into impact craters, and trying to compositionally characterize salt deposits that were left behind as the water evaporated. We also plan to comprehensively characterize tsunami-related morphologies surrounding the entire northern plains basin.
RG: What other research might this discovery inspire?
Rodriguez: There is a lot of research that can be done. But I think we particularly need numerical simulations capable of simulating the tsunami run-up distances from the shorelines and their subsequent backwash phases. The same applies to the dynamic behavior of tsunamis produced from an ice-covered ocean.
Featured image courtesy of the European Southern Observatory.
