Numerous dramatic flood events sculpted the impressive valley system of Kasei Valles on Mars, seen in a new mosaic of 67 individual images acquired by the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft und- Raumfahrt; DLR) on board ESA’s Mars Express spacecraft.
The section of the surface of Mars shown here extends from 280 to 310 degrees east and 19 to 36 degrees north, spanning an area of around 1500 by 1000 kilometres – roughly three times the area of France. The image resolution is 100 metres per pixel. The small colour and brightness variations between the individual image strips in this exceptionally large image mosaic are due to the fact that the images were taken at different times, when the lighting and atmospheric conditions were not the same.
Did volcanoes release the water?
From source to sink, Kasei Valles extends roughly 3000 kilometres. Like many of the striking valleys that run in a conspicuous straight line for great distances, there are many indications that the Kasei valleys were not created by the continuous flow of surface water, but rather by very rare and massive flood events. While their cause is not absolutely clear, it is possible that these flood events are related to volcanic and tectonic activity in the source region, located on the edge of the large Tharsis volcanic region.
The heat that was radiated into the highlands from rising magma bodies may have thawed the ice that was present in cavities under the surface within a relatively short time, causing large volumes of water to rapidly escape. It is also possible that ground water was quickly released along tectonic stress fractures: a striking pattern of fault structures near Sacra Fossae and the huge table-shaped 'island' of Sacra Mensae lying between the two main arms of Kasei indicate the influence of tectonic processes in the region.
The floodwaters followed the topography, making their way to the highlands, which are slightly inclined towards the north. There, they carved the particularly large outflow channel system of Kasei Valles. The volumes of water required for such erosion formations were likely enormous – surely several times the volume of water flowing from the Amazon into the ocean, for example, but in a short period of time. On Earth, a few landscapes caused by a similar process; for example, the Channeled Scablands in the western United States, which were formed by catastrophic floods during the last Ice Age.
Islands, terraces, flow patterns – and traces of the wind
At Kasei Valles, the flowing water and its erosive force left behind typical landscape features such as flow patterns in the valley floor, terraces on the valley walls and droplet-shaped islands sculpted by the floodwaters. Although a great deal of these geological phenomena continue to look well preserved and 'fresh', the water is thought to have flowed through this outflow system some two or even three billion years ago. Multiple valleys were formed by the strong erosive force of the water and the variations in the composition of the substrata, as the water – originally flowing from north to south – was diverted towards the east. It flowed around Sacra Mensa and the Sharanov crater, which are clearly visible as islands in the topographic image map (image 1) and in the perspective view (image 2). Some formations in the terrain also indicate that glaciers, with their erosive force, left their mark on the valley floor and on the slopes to the side.
Increasingly small impact craters can be seen as you zoom in on the large image mosaic (image 4). Some of these have a bright 'dust tail' formed in a streamlined manner, but against the direction of flow of the water. The impacts that generated such craters all took place after the flood events. The dust trails were formed subsequently by the winds blowing up the valley, which deposited the dust and sand on the downwind, leeward side of such craters, which constituted natural obstacles.
Kasei Valles is one of the largest outflow valley systems on our planetary neighbour. The valleys rise further south in Echus Chasma and divide the Martian highlands to the northeast of the large rift valley of Valles Marineris into the uplands of Lunae Planum and Tempe Terra. The Kasei valleys, which are very dendritic at this point, flow into the Chryse plain at the transition from the highland to the lowland. Kasei is the Japanese name for Mars.
Image processing and the HRSC experiment on the Mars Express mission
The images were acquired by the HRSC during 67 different Mars Express orbits. The image resolution is about 100 metres per pixel. The colour image (Image 4) was acquired using the nadir channel, which is directed vertically down onto the surface of Mars, and the colour channels of the HRSC; the perspective oblique view (Image 2) was computed from data acquired with the HRSC stereo channels. The aerial view, encoded in false colours (Image 1), is based on a digital terrain model of the region, from which the topography of the landscape can be derived.
The HRSC camera experiment on board the European Space Agency's Mars Express mission is headed by Principal Investigator (PI) Professor Gerhard Neukum (Freie Universität Berlin), who was also responsible for the technical design of the camera. The science team consists of 40 co-investigators from 33 institutions in 10 nations. The camera was developed at DLR under the leadership of the PI and it was built in cooperation with industrial partners EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH. The instrument is operated by the DLR Institute of Planetary Research in Berlin-Adlershof. The systematic processing of the HRSC image data is carried out at DLR. The images shown here were created by the Institute of Geological Sciences at Freie Universität Berlin in cooperation with the DLR Institute of Planetary Research, Berlin.