Chasma Boreale, Mars: A Sapping and Outflow Channel with a Tectono-thermal Origin

Abstract

apparent head of Chasma Boreale was interpreted as an impact crater. Then, the Viking images showed the crater A detailed geomorphological study of Chasma Boreale, a did not exist, and other questions were raised over the widely known feature of Mars' north polar cap, has been carried out for the first time, along with a quantitative paleohydro-feasibility of the subglacial river.logical model. It is concluded that the chasma was eroded Clifford (1980Clifford ( , 1987 has studied in detail the mechaby a flow whose discharge was on the order of magnitude of nisms for a catastrophic water release from the permafrost, 109 m sec ؊1 . This catastrophic flow is thought to have been looking for analogs on both Earth and Mars. His comparipreceded by a powerful sapping process, caused by a tectoni-son with Ravi Vallis, a box-headed channel on Mars equacally focused thermal event. Several lines of evidence indicate tor (1ЊS, 43Њ) is particularly compelling, because of the tectonic control in the distribution and present aspect of most angular, straight head and huge flow marks. His hypothesis of the polar troughs. This tectonic forcing probably played a of glaciovolcanic outburst water flows (jö kulhlaups of Icemajor role in the inception of not only Chasma Boreale but landic authors) also seems appropriate, since this mechaalso other polar reentrants as well.

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

“…Here, plains are observed beneath the channel wall, and polygonal and dendritic terrain occupies the channel floor. Benito et al [1997] liken some of the polygonal terrain in this region to the braided channels observed in subglacial and proglacial regions. In terms of origin, Benito et al [1997] suggest that at least part of the cap formed along a fault system that allowed heat to be directed to this region, thus causing sapping, which in turn caused outflow.…”

“…Benito et al [1997] liken some of the polygonal terrain in this region to the braided channels observed in subglacial and proglacial regions. In terms of origin, Benito et al [1997] suggest that at least part of the cap formed along a fault system that allowed heat to be directed to this region, thus causing sapping, which in turn caused outflow. The authors argue that this process created the linearity of the chasma, a linearity that is not seen in terrestrial glacial outburst floods.…”

“…If the chasma was initially formed by melting and outflow as suggested by Clifford [1987] and Benito et al [1997], then this volume is probably an overestimate of the volume at the time of initial formation of the chasma due to later enlargement by sublimation and wind erosion. If the chasma was formed purely by wind erosion and sublimation as suggested by Howard [1980Howard [ , 2000, then the initial volume is irrelevant as these processes are ongoing and have presumably, under this scenario, been gradually enlarging the chasma through time.…”

“…[11] A topographic contour map of Chasma Boreale created by Benito et al [1997] using the Viking USGS Digital Elevation Model is shown in Figure 2. The authors estimated the chasma length to be 600 km, the width to be 200 km at its distal end, and the depth to be 500 m. The lowest elevation in the chasma is reached both at the source (0°W) of the chasma (with steep walls), and in the middle portion of the chasma (40°W).…”

“…[8] Benito et al [1997] suggested an origin in which catastrophic outflow of meltwater is triggered by sapping caused by a tectono-thermal event. They map flow features within the northern reaches of Chasma Boreale where the flow is assumed to be the most shallow.…”