Post contributed by David P. Mayer, Department of Geophysical Science, the University of Chicago
Debris-covered glaciers are glaciers whose ablation zones are at least partially covered by supraglacial debris. On Earth, debris-covered glaciers are found in all major mountain glacier systems. The debris itself is primarily derived from rockfall above the accumulation zone. This material becomes entrained in the accumulating ice and is carried englacially before emerging in the ablation zone. On Mars, numerous mid-latitude landforms have been interpreted as debris-covered glaciers based on their geomorphic similarity to nearby ice-rich landforms such as lobate debris aprons (LDA), as well as their similarity to terrestrial debris-covered alpine glaciers (Head et al., 2010 and refs. therein).
Image 1: Aerial photo of Mullins Glacier in Beacon Valley, Antarctica, a debris-covered glacier and possible analog to certain landforms on Mars. USGS aerial photo TMA 3080/275. Available from http://www.pgc.umn.edu/imagery/aerial/antarctica.
Posted by suja82 on June 30, 2016
Post contributed by Dr Veronica Bray, Lunar and Planetary Laboratory, University of Arizona.
Images of Pluto coming back from NASA’s New Horizons spacecraft have revealed many unexpected landforms and show extreme albedo and compositional variations across the dwarf planet’s surface. This blog post concentrates on one high-resolution swath across the boundary between the cratered terrains of Viking and Voyager Terra and the smoother ices of Sputnik Planum (see Figure 1). Take time to scroll down this long image (Figure 2), that covers ~530 km of Pluto’s surface at around 30°N.
Figure 1: A global image of Pluto created from high-resolution (2.2km/pixel) panchromatic images from the LORRI instrument and lower-resolution (5km/pixel) colour data from the Ralph/Multispectral Visual Imaging Camera. The colours have been enhanced to show the diversity of the surface units by combining blue, red and near infra red images. Credits: NASA/JHUAPL/SWRI.
Posted by suja82 on December 1, 2015
Post by Dr. Alberto G. Fairén, Dept. of Astronomy, Cornell University, USA, and Centro de Astrobiología, Spain.
Gale crater, the site of the currently active Mars Science Laboratory (MSL) or Curiosity Rover mission, is a ~154-km-diameter impact crater formed during the Late Noachian/Early Hesperian at the dichotomy boundary on Mars (Cabrol et al., 1999; Anderson and Bell III, 2010; Wray, 2013). The northern floor and rim of Gale are ~1–2 km lower in elevation than its southern floor and rim, and the crater shows a layered central mound named Aeolis Mons, which is 100 km wide, extends over an area of 6000 km2, and is up to 5 km in height (Malin and Edgett, 2000).
Image 1: Details of the lobate features, arcuate ridges and terminal moraines in the central mound of Gale.
Posted by megafloods2013 on September 1, 2014
The current climate on Mars does not allow for significant accumulations of surface ice at low latitudes. Therefore ice is only found at the two polar ice caps and in a number of ice-filled craters scattered at northern and southern latitudes (> 70°).
Image 1 : Extent of Late Noachian – Early Hesperian glaciation and location of supraglacial landslides in Valles Marineris (Gourronc et al., 2014).
Posted by megafloods2013 on May 29, 2014
1Assistant Research Planetary Scientist, UC Santa Cruz, USA. 2Planetary geosciences group, Brown University, Providence, Rhode Island, USA.
On Earth, cold-based glaciers (glaciers deforming internally, without basal melting and basal sliding) are found in the coldest environments (e.g., Antarctica, Marchant et al., 1993). Unlike the majority of glaciers, cold-based glaciers do not scour their substrate and leave pre-glacier topography unaffected. When cold-based glaciers advance and then dynamically stabilize (the ice flow is balanced by frontal ice ablation); debris carried forward by the glacier drops out at the glacial fronts as sublimation of the ice occurs; the dropped material produces so-called drop moraines.
In three locations at high northern latitudes of Mars, overlapping small ridges of arcuate planforms associated with slopes were interpreted as drop moraines left by extinct cold-based glaciers (Garvin et al., 2006; Kreslavsky and Head, 2011). Image 1 shows one of these locations, where a presumable glacier was formed at south-eastern part of an impact crater rim. The shapes of the extinct glacial lobes around the central peak of the crater suggest a few hundred meters thickness of the glacier.
Image 1: Unnamed impact crater in the Northern Lowlands on Mars at 70.3oN, 266.5oE with loop-shaped ridges interpreted as drop moraines created by carbon dioxide glaciers. Image captured by Context Camera onboard Mars Reconnaissance Orbiter, image number T01_000876_2505 Illumination is from lower left.
Posted by megafloods2013 on September 16, 2013
Mars’s Athabasca Vallis is a 10 km wide, 300 km long channel carved by floods originating in the Cerberus Fossae. Recent images acquired by the HiRISE instrument aboard the Mars Reconnaissance Orbiter provides strong evidence that the head reaches of Athabasca Vallis experienced repeated cycles of freezing, with the development of ground ice and polygonised terrain, and warming, marked by ground ice thaw.
Image 1: Retrogressive thaw slumps (RTSs) on the inclined margins (examples marked A) of thermokarst depressions (examples marked B). RTSs have steep, shallow headwalls fronted by inclined flow slumps. Thaw consolidation and ground lowering precedes retrogressive backwearing of the headwall (Czudek and Demek, 1970). RTS headwalls are often facetted due to retrogression exploiting exposed, thawing ice wedges spatially arranged in polygons. Thaw fluids transported through gullies and channels on the slump, from melting ground ice exposed in the headwall, are stored in the depressions fronting the RTSs. However, depressions frequently merge by the retrogressive erosion of inter-depressions. When this occurs, fluid in the higher depression may be tapped into the lower through breaches (examples arrowed), exposing the floor of the drained depression. So, as the depressions fronting these RTSs filled and later drained by tapping, residual taliks froze, epigenetic polygons formed on the exposed floor due to ice segregation and heave and pingos formed by the intrusion of pressurised liquid water into the frozen surface and/or by the freezing of enclosed taliks (e.g. at point of arrow marked C). The resulting “alas” form is a basin with an undulating floor pierced by conical pingo mounds and enclosed by gentle polygonised slopes. White boxes are approximate footprints of Images 2 and 3. All Mars images are sub-scenes from HiRISE image PSP_007843_1905. Image credit NASA/JPL/UofA.
Posted by megafloods2013 on September 13, 2013
Glacial and fluvial landforms that date to ancient Noachian and Hesperian times indicate an abundance of liquid water on Mars at that time. Of interest is evidence of younger (i.e., Amazonian) glacial activities. These processes have recently been suggested for some locations in the Marmers Valles region of Mars [Kress et al., 2006; Di Achille and Ori, 2008; Tirsch, 2009a] (Image 1).
Image 1: Crater near Mamers Valles (HRSC orbit 3304, perspective view, north is to the left).
Posted by megafloods2013 on September 13, 2013
At the north pole of Mars lies Planum Boreum, a dome of layered, icy materials similar in some ways to the large ice caps in Greenland and Antarctica and comparable in size to the former. The dome itself consists of the polar layered deposits, consisting of over 90% ice with a little bit of dust, and the basal unit, consisting of ice, dust, and sand.
An enhanced color image from the Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) shows a portion of the martian north polar layered deposits, the basal unit, and the Olympia Undae dune field. The image is 1.2 km (0.75 mi) across. This image is best understood if you imagine yourself flying over a cliff in a plane. Note that the colors in an enhanced color image do not re-create what it would look like to the naked, human eye, but rather bring out the compositional differences between the materials.
Posted by megafloods2013 on September 11, 2013
Lobate debris aprons (LDA) are distinctive geomorphic landforms showing evidence for the creep and deformation of ice-rich debris in Martian mid-latitudes [e.g., Carr and Schaber, 1977; Squyres, 1978, 1979; Lucchitta, 1984].
Image 1: The image shows a textbook example of a typical Martian lobate debris apron, considered to be a mixture of ice and rocky particles (rock glaciers are a terrestrial analog). The lobate flow front and the convex-upward profile are characteristic for these phenomena. The data were acquired on May 29, 2004 with the Mars Express High Resolution Stereo Camera (HRSC). The 3D-perspective in this image was rendered to simulate an oblique view from the north. The mountain with the lobate debris apron is centered at 40.60 S and 103.01 E, in the Promethei Terra region, very close to Reull Vallis.
Posted by megafloods2013 on September 10, 2013