Debris flows on Earth and Mars

• Main Author: Conway, Susan Jane
• Published: Open University 2010
• Subjects: 551.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520681

This thesis explores the morphology of debris flows and their role in shaping planetary surfaces. The primary objective is to assess the scale of the present martian near-surface water budget by studying recent gullies visually similar to water-carved gullies on Earth. The potential involvement of debris flow in forming these gullies is important, because it implies the action of liquid water. To assess the role of debris flow in forming martian gullies requires a better understanding of debris flows on Earth. I first performed a detailed study of unconfined debris flows in NW Iceland and developed a model to predict their path and deposition thickness using only the morphology of the previous deposits. I used this model to define areas at risk from debris flow inundation. Secondly I have used quantitive geomorphological methods to study long profiles and digital elevation models and have successfully ascertained the geomorphic “fingerprint” of mass wasting, debris flow and pure water flow on Earth. Using these methods, I then confirmed that gullies on Mars contain the signature of debris flow. In addition, these investigations revealed a strong climatic signal in gully development. Laboratory simulation experiments showed that under present martian climate liquid water can not only survive for appreciable time-scales, but can perform significant geomorphic work. Freezing at the base of the flow not only decreases infiltration, but increases the runout of the flow. These results indicate that gullies are a product of the recent action of thaw of ice on Mars. I suggest that moderate orbital spin obliquity is required to form gullies (rather than high obliquity suggested previously), because this is consistent with their distribution, the time needed for their development, and their relative youth. Thus the surface of Mars has been wetter, more recently than previously thought.