Scientists: Viking-1 might have landed on a field of Martian tsunami debris

The geological history of the Viking-1 Mars landing site

As outlined in their new paper [pdf], a team of scientists now hypothesize that the features that surrounded Viking-1 when it landed on Mars in 1976 were caused by two past Martian tsunamis. Each tsunamis occurred due to an impact in the theorized ocean that is believed to have existed in this part of Mars’ northern lowland plains several billion years ago.

The graphic to the right, figure 8 from the paper, shows the hypothesized sequence of events. From the caption:

(a) Pohl crater forms within a shallow marine environment, (b) triggering tsunami water and debris flow fronts. (c) The wave fronts extensively inundate the highland lowland boundary plains, including a section ~ 900 km southwest of the impact site. (d) The ocean regresses to ~ − 4100 m, accompanied by regional glacier dissection, which erode the rims of Pohl and other craters. (e) The younger tsunami overflows Pohl and parts of the older tsunami. Glaciation continues, and mud volcanoes later source and emerge from the younger tsunami deposit. (f) ~ 3.4 billion years later, the Viking 1 Lander touches down on the edge of the older tsunami deposit.

The overview map below provides the larger context.
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Mars’s giant tsunamis

New research using data from a variety of Mars orbiters suggests that large tsunamis previously smashed against the shores of the red planet, shaping the geography.

The group zeroed in on a region on Mars where the highlands known as Arabia Terra bump up against the lowlands of Chryse Planitia — a place where the waters of an ancient ocean might have lapped at the shoreline. Using imagery from several Mars-orbiting spacecraft, Rodriguez’s group identified two particular geological formations that they say formed during two different tsunamis. The first, older formation looks as if an enormous wave had rushed up onto the edge of the highlands, dropping boulders as big as 10 metres across. The water then drained back down into the ocean, leaving channels cut through the freshly deposited debris.

Then, millions of years passed. Temperatures dropped and glaciers crept across the landscape, scouring deep valleys. Finally, a second impact-generated tsunami came rushing again towards the shore. “But this time it is different,” Rodriguez says. Because the climate was so much colder, the tsunami moved over the landscape like an icy slurry. It froze before it had a chance to wash back into the ocean, leaving dense lobes of frozen debris on the ground.

They propose the waves were caused by large meteorite impacts. They also admit that there are large uncertainties in their theory and conclusions.