Debris Flow Gullies at the Great Kobuk Sand Dunes, Alaska: Implications for Analogous Features on Mars

Debris flows with fresh-appearing gullies or erosion tracks occur on the slopes of several mid- to high-latitude dune fields in both Martian hemispheres. These features originate in alcoves near dune crests, become channelized down lee faces, and terminate with depositional fans. They bear a striking resemblance to small meltwater-induced debris flows observed on the lee slopes of large dunes at the 67 degrees N latitude Great Kobuk Sand Dunes (GKSD), Kobuk Valley National Park, Alaska. The high-latitude, cold-climate GKSD are an optimal terrestrial system within which to conduct a Mars analog study focused on understanding the integrated factors that cause alluvial debris flows to initiate on the lee slopes of aeolian dunes. Debris flow processes in the GKSD are activated by seasonal thawing and consist of a mixture of sand and liquid water cascading down the dune slipface. A distinguishing environmental attribute that separates cold-climate dune fields from temperate and warm-climate dune fields is the seasonal and prolonged occurrence of snow and ice. Cold region dunes often include niveo-aeolian deposits composed of interbedded sand, snow, and ice. The GKSD are variably affected by snowcover for ~70% of each year, which likely has direct analogy to hydrocryospheric factors that influence debris flow development on Mars. Melting and/or sublimation of snow and ice during warm periods cause distinctive morphologic and sedimentologic phenomena ascribed as denivation features or forms, including spongy and hummocky surfaces, tensional cracks, deformed strata, slumping, and compressional structures. We observed small debris flows, niveo-aeolian deposits, and denivation features in the GKSD during fieldwork in March 2010. Wind-transported sand and snow accumulated on the lee slopes of large transverse, longitudinal, and barchanoid dunes. Snow banks with intercalated sand layers are especially prominent and thickest near the top of westward-facing lee slopes at the GKSD. Small debris flows induced by snowmelt were observed on the lee slopes of large dunes and usually terminated in meltwater alluvial fans that exhibited a lobate flow-front morphology. We propose that these debris flows are generated when high pore-water pressures develop in thawed, near-surface niveo-aeolian deposits due to impeded infiltration by frozen sand and pore ice. The melting of niveo-aeolian deposits is one possible trigger for generating both terrestrial and Martian debris flows and is a likely mechanism in the formation of the associated gullies. Detailed knowledge of the processes involved in niveo-aeolian transport, deposition, and reworking is relatively sparse and poorly understood. Our investigation provides insights into the interactions between niveo-aeolian deposition, thawing, insolation, slope aspect, and initiation of alluvial processes.