Ancient mega-floods in Kasei Valles on Mars

Kasei Valles (Photo ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO)
Kasei Valles (Photo ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO)

ESA has published new photos of the Kasei Valles channel system on Mars captured by the Mars Express space probe’s High Resolution Stereo Camera (HRSC) instrument. The collected data indicate that Kasei Valles were generated by a series of mega-floods and not by a continuous water flow on the surface. Today this system of channels is one of the largest on Mars and extends for 3,000 kilometers (almost 1,900 miles) from Echus Chasma, near Valles Marineris, up to Chryse Planitia.

It’s not the first time that research on the history of Mars indicate that once those regions were hit by violent phenomena. The most striking example is a study published in May 2016 in the journal “Nature” which described two possible mega-tsunamis that shook the red planet’s surface. Some research focused on the geological history of Kasei Valles, with channels that cover very long distances, a feature that led to the conclusion that they formed as a result of individual mega-floods.

Between 3.6 and 3.4 billion years ago, a combination of volcanism, tectonic collapse and subsidence in the neighboring region of Tharsis led to massive releases of water on the surface to Echus Chasma. The result was the series of mega-floods that generated the channels visible today. The traces of these ancient events are not visible only in those channels but also in other areas such as Worcester crater.

Various craters were generated by impacts in that region before the floods began to radically change its appearance. With its 25 kilometers (about 15.5 miles) in diameter, Worcester crater is the largest and stood up well to the floods’ erosive forces. Its rimas about 1.5 km (almost 1 mile) high form an obstruction in the middle of the valley and the impact had compacted the rocks, making them more resistant to flooding than the less compact materials around it.

The area around Worcester crater looks different depending on their position relative to the floods’ flow. The situation of the adjacent crater is quite different as the debris surrounding it remained intact, a situation that indicates that it was generated by an impact after the floods. The debris also suggest that the flood plain was full of water or water ice.

The crater in the upper right corner of the image shows more features. It doesn’t seem to be penetrated in the soil as much as Worcester and its neighbor and that’s due to the fact that it’s located on a plateau that is at least a kilometer higher than the plains below. Despite this there’s a small depression in the center of the crater and this normally means that there’s a weaker layer, which may be for example of ice, buried under it at the impact moment.

The characteristics of the materials ejected from that crater are also different from those of the materials ejected from the other craters. Maybe the impact was different in the energy given off and the way the materials were placed coming from the crater but also in the composition of the materials present in the plateau. Small dendritic channels are visible all around the plateau, which could indicate various levels of intensity of the floods.

All this shows once again that when it was young, Mars was much more like the Earth, with so much liquid water on the surface that there could be violent events. In this case, the traces also show the volcanic activity of the time and the influence it could have on the environment.

Perspective view towards Worcester crater (Image ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO)
Perspective view towards Worcester crater (Image ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO)

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