Lobate debris aprons (LDAs) are geological features onMars, first seen by theViking Orbiters, consisting of piles of rock debris below cliffs.^[1][2] These features have a convex topography and a gentle slope from cliffs orescarpments, which suggest flow away from the steep source cliff. In addition, lobate debris aprons can show surfacelineations as do rock glaciers on the Earth.^[3]

• 
  Wide view of mesa with CTX showing cliff face and location of lobate debris apron (LDA) Location isIsmenius Lacus quadrangle.
• 
  Enlargement of previous CTX image of mesa. This image shows the cliff face and detail in the LDA. Image taken withHiRISE underHiWish program. Location isIsmenius Lacus quadrangle.
• 
  Lobate debris aprons (LDAs) around a mesa, as seen by CTX. Mesa and LDAs are labeled, so one can see their relationship. Radar studies have determined that LDAs contain ice; therefore, these can be important for future colonists of Mars. Location isIsmenius Lacus quadrangle.
• 
  Close-up of lobate debris apron (LDA), as seen by HiRISE under HiWish program
• 
  Lobate debris apron inPhlegra Montes, as seen by HiRISE. The debris apron is probably mostly ice with a thin covering of rock debris, so it could be a useful source of water. Scale bar is 500 meters (1,600 feet) long.
• 
  Close-up of surface of a lobate debris apron inHellas quadrangle. Note the lines that are common inrock glaciers on the Earth.
• 
  Place where a lobate debris apron begins. Note stripes which indicate movement. Image located inIsmenius Lacus quadrangle.

• 
  Wide view of mesa with surrounding lobate debris apron, as seen by CTX. Part of this picture is enlarged in the following HiRISE image. Location is the Ismenius Lacus quadrangle.
• 
  Part of lobate debris apron, as seen by HiRISE under HiWish program This lobate debris apron surrounds a mesa. Location is the Ismenius Lacus quadrangle.
• 
  Lobate debris apron around mesa, as seen by HiRISE under HiWish program
• 
  Close view of lobate debris apron around mesa, as seen by HiRISE under HiWish program.Brain terrain is visible.

TheMars Reconnaissance Orbiter's Shallow Radar gave a strong reflection from the top and base of LDAs, meaning that pure water ice made up the bulk of the formation (between the two reflections).^[4] This is evidence that the LDAs inHellas Planitia areglaciers covered with a thin layer of rocks.^{[5][6][7][8][9]} In addition, radar studies inDeuteronilus Mensae show that all lobate debris aprons examined in that region contain ice.^[10]

Analysis ofSHARAD data led researchers to conclude that Lobate debris aprons (LDA's) are over 80% pure ice. The paper authors examined five different sites from around the planet and all showed high levels of pure water ice.^[11][12][13]

Because of the high purity of the ice content that was found, the authors argued that the formation of glaciers happened by atmospheric precipitation or direct condensation. After glaciers were formed there was a time when enhanced sublimation formed a lag layer or promoted the accumulation of dry debris atop the water ice glacier. Those dry debris would then insulate the underlying ice from going away.^[14]

The experiments of thePhoenix lander and the studies of theMars Odyssey from orbit show thatfrozen water exists just under the surface of Mars in the far north and south (high latitudes). Most of the ice was deposited as snow when the climate was different.^[15] The discovery of water ice in LDAs demonstrates that water is found at even lower latitudes. Futurecolonists on Mars will be able to tap into these ice deposits, instead of having to travel to much higher latitudes. Another major advantage of LDAs over other sources of Martian water is that they can easily be detected and mapped from orbit. Lobate debris aprons are shown below from the Phlegra Montes which are at a latitude of 38.2 degrees north. The Phoenix lander set down at about 68 degrees north latitude, so the discovery of water ice in LDAs greatly expands the range of water easily available on Mars.^[16] It is far easier to land a spaceship near the equator of Mars, so the closer water is available to the equator, the better it will be for colonists.^{[citation needed]}

The floors of some channels show ridges and grooves that seem to flow around obstacles; these features are called lineated floor deposits orlineated valley fill (LVF). Like lobate debris aprons, they are believed to be ice-rich. Some glaciers on the Earth show such features.

It has been suggested that lineated floor deposits began as LDAs.^[17][18] By tracing the paths of the curved ridges characteristic of LDAs, researchers have come to believe that they straighten out to form the ridges of LVF.^{[19][20][21][22]} Both lineated floor deposits and lobate debris aprons often display a strange surface formation calledbrain terrain because it looks like the surface of the human brain.^[23]

• 
  Wide CTX view showing mesa and buttes with lobate debris aprons and lineated valley fill around them. Location isIsmenius Lacus quadrangle.
• 
  Close-up oflineated valley fill (LVF), as seen by HiRISE under HiWish program. This is an enlargement of the previous CTX image.
• 
  Wide CTX view of mesa showing lineated valley fill and lobate debris apron (LDA). Both are believed to be debris-covered glaciers. Location isIsmenius Lacus quadrangle.
• 
  Close-up of lobate debris apron from the previous CTX image of a mesa. Image shows open-cell brain terrain and closed-cellbrain terrain, which is more common. Open-cell brain terrain is thought to hold a core of ice. Image is from HiRISE under HiWish program.
• 
  Closed-cell brain terrain, as seen by HiRISE under the HiWish program. This type of surface is common on lobate debris aprons, concentric crater fill, and lineated valley fill.
• 
  Open and closed-cell brain terrain, as seen by HiRISE, under HiWish program.

Reull Vallis, pictured below, displays these deposits.^[24] Sometimes the lineated floor deposits show a chevron pattern, which is further evidence of movement. The picture below taken with HiRISE of Reull Vallis shows these patterns.

Recent analyses of theNereidum Montes (~35°- 45°S, ~300° - 330°E), andPhlegra Montes (NNE - SSW, between latitudes 30° - 52°N) mountain ranges ofMars have revealed terrains rich inviscous flow features (VFFs), a cyro-geomorphological group of which lobate debris aprons are a sub-class. In a 2014 study, 11,000 VFFs have been recorded between 40° and 60° in northern and southern latitudes, with a 2020 study identifying approximately 3,348 VFFs in theNereidum Montes range.^[25][26] These LDAs were more extensive and older VFF features (hundreds of Ma) in the range, with the vast majority located in impact craters and surroundingmassifs.^[25]

Water-ice tolithic ratios of 9:1 were recorded for LDAs by theMars Reconnaissance Orbiter (MRO), with Berman's 2020 study presentingNereidum Montes as possibly containing more water-ice rich LDAs, than other locations in the mid-latitude band.^[25][27] Studies have estimated that LDAs could reach from tens of meters up to 390 meters (1,280 feet) in thickness, with anywhere from 1 to 10 meters (3.3 to 32.8 feet) of overlyingregolith preventing sublimation.^[27][28][29]Late Amazonianglaciation may have occurred in the mid-latitudes due to water-ice emplacement from higher latitudes. Thisglaciation may have occurred duringhigh obliquity periods inMars past.^{[25][29][30][31]} Some of these LDAs are overlain with another class of viscous ice flows that is smaller, and younger (tens of Ma) calledglacial-like flows (GLFs). Some 320 of these superposed GLFs (SGLFs) have been found, implying successive glaciation periods.^[31]

The datasets utilized in these studies included MRO Context Camera (CTX; ~5–6 m/pixel), High-Resolution Imaging Science Experiment (HiRISE) (~25 cm/pixel) images, MRO Shallow Radar (SHARAD), 128 pixel/degree (~463 m/pixel) Mars Global Surveyor (MGS),Mars Orbiter Laser Altimeter (MOLA),Digital Elevation Modelling (DEM), 100 m/pixelTHEMIS Day and Night IR mosaics, and the GIS-based (ESRI ArcGIS Desktop) software.^{[25][28][29][30][31][32][33]}

Lobate debris aprons (LDA's) and lineated valley fill (LVF) are now thought to be the same--mostly ice with a covering of debris, their shapes are dependent on their locations. When confined within a valley, LVF is present; in contrast when not confined, this flowing debris covered ice forms LDA's.^[34]

• 
  Map of the eastern part ofHellas Planitia (a vast impact crater), showing two large river valleys that slope left, toward the floor of the crater.
• 
  Reull Vallis with lineated floor deposits, as seen byTHEMIS. Click on image to see relationship to other features.
• 
  Niger Vallis with features typical of this latitude, as seen byHiRISE. Chevron pattern results from movement of ice-rich material. Click on image to see chevron pattern and mantle.
• 
  Material moving down slope inPhlegra Montes, as seen byHiRISE. Movement is probably aided by water/ice.

• Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention
• Jeffrey Plaut - Subsurface Ice - 21st Annual International Mars Society Convention

• Geology of Mars
• Surface features of Mars

• All articles with dead external links
• Articles with dead external links from July 2022
• CS1 maint: multiple names: authors list
• CS1 errors: missing title
• CS1 errors: bare URL
• Articles with short description
• Short description matches Wikidata
• All articles with unsourced statements
• Articles with unsourced statements from October 2020