Chasma Boreale, Mars: Topographic characterization from Mars Orbiter Laser Altimeter data and implications for mechanisms of formation

Abstract

[1] Chasma Boreale, a large reentrant in the north polar cap of Mars, is distinct in scale, detailed topography, and orientation from the spiraling troughs that characterize the majority of the polar cap. We use new, high-resolution Mars Orbiter Laser Altimeter (MOLA) data and Mars Orbiter Camera (MOC) and Viking images of the chasma region to assess hypotheses of origin of Chasma Boreale. These hypotheses include formation by glacial flow and ablation, by eolian processes (such as katabatic winds) and sublimation, by outflow of meltwater, or by a combination of two or more of these processes. We find that these new data support initial formation by outflow of meltwater with later modification by katabatic winds and sublimation. On the basis of our analysis we suggest a possible scenario in which outflow has occurred in several stages. The outflow appears to have begun near an enclosed depression at the head of the chasma; meltwater migrated within and below the ice down the regional slope and eventually broke out to the surface. Removal of material by melting caused subsidence and erosion of the polar deposits forming the chasma, which has subsequently undergone modification by eolian and sublimation processes. The outflow deposited most of its sediment in the form of a lobe that stratigraphically overlies the polygonal plains mapped at the mouth of the chasma and scoured some of the circumpolar sediment mantle in the surrounding region. The lowest portions of the North Polar Basin received the rest of the sediment as a deposit a few meters thick. MOLA data also reveal evidence for similar events of smaller magnitude elsewhere on the margins of the polar cap.

Evolution of the north-polar cap of Mars: a modelling study

“…They also report strongly enhanced ice-flow velocities of up to 50 mm a −1 at the steepest scarps, minimum local sublimation rates of 50 mm a −1 required to keep the troughs open in time and inward-migration speeds of the troughs of tens of centimeters per year. Fishbaugh and Head (2002) discussed possible formation mechanisms of Chasma Borealis. Based on an analysis of high-resolution MOLA data and Mars Orbiter Camera (MOC) and Viking images of the region, they favoured a formation scenario by meltwater outflow (probably in a jökulhlaup-type event) with subsequent shaping by sublimation and eolian processes.…”

The construction of Chasma Boreale on Mars

“…Stratigraphic analyses of the exposed portions of Chasma Boreale-a large canyon 500 km long, up to 100 km wide, and nearly 2 km deep-have led most researchers to favour an erosional process for its formation following initial NPLD accumulation. Candidate mechanisms include the catastrophic outburst of water 5 , protracted basal melting 6 , erosional undercutting 7 , aeolian downcutting [7][8][9] and a combination of these processes 10 . Here we use new data from the Mars Reconnaissance Orbiter to show that Chasma Boreale is instead a long-lived, complex feature resulting primarily from non-uniform accumulation of the NPLD.…”

Scenarios for the formation of Chasma Boreale, Mars

“…A possible explanation for its origin is a jökulhlaup (glacial outburst flood) induced by a temporary heat source under the ice due to a tectono-thermal or volcanic event (Clifford 1980a,b, 1987, 1993, Benito et al 1997, Fishbaugh and Head 2002. Support for this mechanism is provided by the likely identification of geologically young volcanic craterforms on the floor of Chasma Boreale and near its mouth (Hodges and Moore 1994, Garvin et al 2000a,b, Sakimoto et al 2000.…”