Delta and fan morphologies on Mars as climate indicators

Abstract

The presence, duration and quantity of water on Mars remains an important research topic in planetary science. Large valley networks, regional outflow channels, and small-scale gullies indicate the presence of water on the surface at certain points in the past. However, the climatic history and evolution is poorly understood and reconstruction of the early climate is still uncertain, and most importantly, the quantity of water and its spatial and temporal extent on the surface is still unknown. The surface is host to a large variety of landforms that were studied using remote sensing satellite data from ESA (European Space Agency) and NASA (National Aeronautics and Space Administration). Different landforms, including mainly deltas and other fan-shaped sedimentary deposits, as well as shallow-marine impact craters, are investigated in order to infer climate conditions at the time that these features were formed. By studying the geomorphology of landforms on Mars and comparing them to the geomorphology of similar landforms on Earth and in the laboratory, important features such as length of time of formation, initial water level (if any), and upstream conditions can be deduced; all of which may be used to interpret the climate history of the planet. This thesis includes research on a) satellite observations of shallow-marine impact craters and of fan-shaped sedimentary deposits (the equivalent of ‘field-work’ on Mars), b) descriptions of terrestrial analogues for Martian alluvial fans in the Atacama Desert (real field-work on Earth), c) experimental laboratory work with emphasis on the creation of deltas in crater lakes and with some terrestrial application to the study of river-morphodynamics during dam removal, and d) numerical modelling of sediment transport and formative processes for delta deposits on Mars, in order to deduce the length of time required to form these deposits and ultimately, to infer the climate conditions at the time of formation. From the satellite observations of shallow-marine impact craters in selected regions, it is suggested that the duration of extensive oceans may have been limited. From the satellite observations of all fan-shaped sedimentary deposits on Mars, it is observed that distinctly different classes of deposits exist and that most of these deposits have morphologies indicating short formation times. From the description of terrestrial analogues for alluvial fans, it is proposed that Martian alluvial fans may have been formed predominantly by debris-flow events instead of by run-off. From the laboratory experiments in combination with simple numerical modelling, it is concluded that most delta morphologies on Mars were likely constructed by single, catastrophic, short-duration flow events in which large quantities of water flowed over the surface in short periods of time. This thesis concludes that even though water has played a crucial role in shaping the landscape of Mars, there is limited evidence of a long-duration, stable hydrological cycle that could have supported long-lived oceans. The author favours a predominately cold and dry climatic history for the planet Mars, with intermitted pulses of hydrological activity that are capable of producing the landforms that are studied in this thesis.