Mars’ Ancient Mega-Floods Are Still Etched Into the Red Planet

Around 3.5 billion years ago — when basic life was just gaining a foothold on Earth — the Tharsis region on Mars was swamped with vast floods that scar the landscape to this day.

perspective_view_towards_worcester_crater
Rendered perspective view of Worcester Crater using Mars Express elevation data. The dramatic crater rim was carved by the flow of ancient floodwater (ESA)

Mars wears its geological history like a badge of honor — ancient craters remain unchanged for hundreds of millions of years and long-extinct volcanoes look as if they were venting only yesterday. This is the nature of Mars’ thin, cold atmosphere; erosional processes that rapidly delete Earth’s geological history are largely absent on the Red Planet, creating a smorgasbord of features that provide planetary scientists with an open book on Mars’ ancient past.

In this latest observation from the European Mars Express mission, a flood of biblical proportions has been captured in all its glory. But this flood didn’t happen recently, this flood engulfed a vast plain to the north of the famous Valles Marineris region billions of years ago.

It is believed that a series of volcanic eruptions and tectonic upheavals in the Tharsis region caused several massive groundwater releases from Echus Chasma, a collection of valleys some 100 kilometers (62 miles) long and up to 4 kilometers (2.5 miles) deep. These powerful bursts of water carved vast outflow channels into the adjacent Lunae Planum, contributing to the formation of the Kasei Valles outflow channels, releasing water into the vast Chryse Planitia plains which acted as a “sink.” Smaller “dendritic” channels can be seen throughout the plain, indicating that there were likely many episodic bursts of water flooding the region.

This context image shows a region of Mars where Kasei Vallis empties into the vast Chryse Planitia (NASA MGS MOLA Science Team)
This context image shows a region of Mars where Kasei Vallis empties into the vast Chryse Planitia (NASA MGS MOLA Science Team)

These floods happened between 3.4 to 3.6 billion years ago, less than a billion years after the most basic lifeforms started to appear on Earth (a period of time known as the Paleoarchean era).

In the middle of what was likely a powerful, vast and turbulent flows of water is Worcester Crater that was created before the Tharsis floods and, though its crater rim stands to this day and retains its shape, it was obviously affected by the flow of water, with a “tail” of sediment downstream.

ESA Mars Express observation of the mouth of Kasei Valles, as it transitions into Chryse Planitia. The large crater in the lower left is Worcester Crater. (ESA/DLR/FU Berlin)
ESA Mars Express observation of the mouth of Kasei Valles, as it transitions into Chryse Planitia. The large crater in the lower left is Worcester Crater (ESA/DLR/FU Berlin)

Also of note are smaller “fresh” craters that would have appeared long after the flooding took place, excavating the otherwise smooth outflow channels. These younger craters have tails that seem to be pointed in the opposite direction of the flow of water. These tails weren’t caused by the flow of water, but by the prevailing wind direction.

From orbital observations by our armada of Mars missions, it is well known that these channels contain clays and other minerals associated with the long-term presence of water. Although the Red Planet is now a very dry place, as these beautiful Mars Express images show, this certainly hasn’t always been the case.

Mars Crater’s Cracked Frosting

Subliming ice from the crater's edge (NASA/JPL/University of Arizona)
Subliming ice from the crater edge (NASA/JPL/University of Arizona)

This image looks like the frosted top of an over-baked muffin, but it’s actually the side of a crater on Mars covered with ice. Taken by NASA’s Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) over the Martian south pole, this example demonstrates an active process of weathering acting on the red landscape. According to the HiRISE site, the ice layer is approximately 3 km thick.

In regions situated closer to the equator, craters aren’t open to erosion by ice (not surface ice in any case), but in polar regions it’s a different story. Due to the Martian thin and cold atmosphere, water ice rarely melts into a liquid; it bypasses the liquid phase and turns straight into a gas. This process is known as sublimation. There are terrestrial examples of sublimation too, including frozen carbon dioxide (or “dry ice”) which sublimes at room temperature, generating a carbon dioxide vapour.

For this particular crater, it is obvious where there is a higher rate of sublimation than others. As the Sun illuminates the crater edge from the bottom right, the rim of the crater receives the most sunlight, heating up the darker regolith and causing more ice loss. The large cracked-like structure within the crater is most likely a combination of darker material under the ice receiving preferential heating and shrinkage of the subliming ice pack.

This seasonal freezing of water vapour and sublimation of water ice erodes the sides of these polar craters, wearing them down season after season.

I never tire of seeing HiRISE images of the Red Planet, especially when they include active atmospheric processes that continue to shape the landscape of this alien world.

Source: HiRISE