Mars Fourth Order Landscapes Geography 441541 S16 Dr

Mars: Fourth Order Landscapes Geography 441/541 S/16 Dr. Christine M. Rodrigue

Mars: Fourth Order Landscapes • The “Orders of Relief” for Martian Landscapes – The first order was the great crustal dichotomy and Tharsis: • Northern lowlands: ~ 1/3 • Southern highlands: ~2/3 • Tharsis Rise: ~1/4 – The second order was the large regional features: • • Elysium Rise The largest craters: Hellas, Argyre, Isidis, Utopia Valles Marineris The polar ice caps

Mars: Fourth Order Landscapes • The “Orders of Relief” for Martian Landscapes – The third order was the somewhat smaller major regions associated with the araeological eras: • In many ways, this is a cross-cutting category • It addresses the “geological column” or relative ages of all Martian landscapes in terms of the three regional units that gave three -part sequences of Mars’ evolution their names: – The Noachian Era – The Hesperian Era – The Amazonian Era

Mars: Fourth Order Landscapes • The “Orders of Relief” for Martian Landscapes – The fourth order is “in order” now: • These are smaller features (a few kilometers to a few hundred km): • They are landscapes dominated by one or two processes – Fluvial valleys – Sapping alcoves – Outwash channels – Linear fossæ – Folded and faulted mountains of Thaumasia – Lava tubes – Layered mesas – Patterned ground – Wind abraded/etched landscapes – Dune fields – Evidence of mass wasting

Mars: Fourth Order Landscapes Secondary cratering issue: (W. K. Hartmann painting http: //psi. edu/hartmann/)

Mars: Fourth Order Landscapes • Secondary cratering issue: – Secondary cratering from a primary impact event can be hard to detect – odd-shaped craters are often described as secondaries – lower velocity impacts don't produce a symmetrical detonation

Mars: Fourth Order Landscapes • Secondary cratering issue: – Secondary cratering from a primary impact event can be hard to detect just from odd shapes – Plot complication: really low angle impacts, <15° , can also produce odd shapes, if rarely ° Orchus Patera (340 x 140 km)? ° Terra Sabæa near Huygens (80 x 20 km) ° crater N of Acheron Fossæ

Mars: Fourth Order Landscapes • Secondary cratering issue: – Secondary cratering often produces linear chains of craters – THEMIS, +19 at 348 E( Trouvelot Crater) – MOC, +16 at 325° (Margaritifer Terra) – MRO image of Candor Chasma wall with this weird chain cutting across at an angle to gravity – This can result from forces in the ejecta curtain organizing the debris into linear, unsorted rays, as seen (and preserved) on the moon

Mars: Fourth Order Landscapes • Secondary cratering issue: – My attempt to detect crater rays – 6 th order nearest neighbors – calculated azimuths from each crater to its 6 th order nearest neighbors – compensated for random “alignments” by counting craters at various standards of “alignment” and comparing the counts with the binomial distribution using a Chi-square goodness-of -fit test – a <15° departure of azimuths from that of the nearest neighbor pair was considered “aligned”

Mars: Fourth Order Landscapes • Secondary cratering issue: – My attempt to detect crater rays came out kinda groovy!

Mars: Fourth Order Landscapes • Secondary cratering issue: – Robbins and Head (2011) – mapped crater clusters – drew great circle routes – several great circles converged on Lyot Crater north of Arabia Terra

Mars: Fourth Order Landscapes • Folded and Faulted Mountains: – Grabens and folds – Thaumasia Highlands

Mars: Fourth Order Landscapes • Lava Tubes: – Lava flows under a crust, which may collapse – Pavonis – Check out catena

Mars: Fourth Order Landscapes • Lava Tubes: – Lava flows under a crust, which may collapse – Pavonis – Check out catena inside a graben or dike or lava tube

Mars: Fourth Order Landscapes • Layered Mensæ: – Resistant caprocks protect less resistant materials below – Artist: Marilynn Flynn www. tharsisartworks. com

Mars: Fourth Order Landscapes • Layered Mensæ: – Resistant caprocks protect less resistant materials below – Cydonia and the Face on Mars

Mars: Fourth Order Landscapes • Layered Mensæ: – Resistant caprocks protect less resistant materials below – Cydonia – Face with HRSC and MOC

Mars: Fourth Order Landscapes • Layered Mensæ: – Resistant caprocks protect less resistant materials below – The heart on Mars south polar region, ~255 m across

Mars: Fourth Order Landscapes • Faces of Other Species, too! – Flow of younger lava? – The Elephant on Mars – Thanks to Ms. Stoddard – Okay, not a mensa. . .

Mars: Fourth Order Landscapes • Yardangs: – Erosional æolian features – – Classic sandblasting south of Olympus Mons taken by HRSC (Mars Express) near +6 by 220 Earth grooved terrain/yardangs (military source: location unknown)

Mars: Fourth Order Landscapes • Yardangs: – Erosional æolian features – – Interesting parallel between Earth yardangs (again some unspecified military source) and Mars yardangs and layered terrain The Mars yardangs (top) are from Æolis Mensæ, just south of Elysium on the margins of the southern highlands

Mars: Fourth Order Landscapes • Dunes: – Depositional æolian features – Classic barchans in Nili Pateræ, a volcanic depression in Syrtis Major

Mars: Fourth Order Landscapes • Dunes: – Depositional æolian features – Dune field in Endurance Crater imaged by Opportunity – Closest ridges < ~1 m – Blue color in slacks between dune crests reflect hæmatite blueberries – Lighter dust accumulates more on the lip of the crests than on the flanks – Like Earth star dune fields, probably reflect an unpredictable wind regime, as seen in this mystery military image (below)

Mars: Fourth Order Landscapes • Dunes: – Depositional æolian features – Endurance Crater and its load of dunes

Mars: Fourth Order Landscapes • Patterned Ground: – Polygons and permafrost – Mars -72 at 29 (MOC) – Earth NW Territories, Canada, Sharon Johnson’s Geo. Images, UC Berkeley – Stresses from: – Freeze-thaw of water – Expansion-contraction of other materials with temperature changes – Sorting of rock material in the polygon boundaries

Mars: Fourth Order Landscapes • Patterned Ground: – Polygons and permafrost – Close up of boulders and other larger clasts caught in the boundaries among polygons

Mars: Fourth Order Landscapes • Eskers: – Subglacial streams – Basal melt feeds streams – Stream beds later exposed as sinuous, gravelly ridges – Dorsa Argentea, north of the South Polar Ice Cap Basal Unit, southwest of Hellas, southeast of Argyre

Mars: Fourth Order Landscapes • Mass Wasting: – Landslides – Common on crater gully walls at a small scale – Very evident as a major mechanism for the expansion of Valles Marineris – Ganges Chasma – Noctis Labyrinthus

Mars: Fourth Order Landscapes • Mass Wasting: – Landslides – Common on crater gully walls at a small scale – Very evident as a major mechanism for the expansion of Valles Marineris – South Candor Chasma

Mars: Fourth Order Landscapes • Mass Wasting: – Chaos – Collapsed, jumbled terrain – May be source of massive outflows, possibly explosive if CO 2 is involved – Aram Chaos, which seems to feed into Ares Vallis

Mars: Fourth Order Landscapes • Softened Craters: – Rims eroded – Burns Ridge (Opportunity) – Floors filled – Dust and ice (Mars Exp)

Mars: Fourth Order Landscapes • Softened Craters: – Rims eroded possibly by oceanic currents and processes before the northern lowlands dried out or were resurfaced with younger lavas – Ground penetrating radar (MARSIS on ESA Mars Express)

Mars: Fourth Order Landscapes • Softened Craters: – Floors filled – Water – alluvial fans in Eberswalde Crater (below) – Floors re-excavated by wind – Arabia Terra crater layers (to right)

Mars: Fourth Order Landscapes • Softened Craters: – Floors REALLY worked over – Arabia Terra Crater (MOC)