77°28′S162°31′E / 77.467°S 162.517°E /-77.467; 162.517
TheMcMurdo Dry Valleys are a row of largelysnow-free valleys inAntarctica, located withinVictoria Land west ofMcMurdo Sound.[1] The Dry Valleys experience extremely low humidity and surrounding mountains prevent the flow of ice from nearbyglaciers. The rocks there aregranites andgneisses, and glacialtills dot thisbedrock landscape, with loose gravel covering the ground. It is one of the driest places on Earth,[2] though there are several anecdotal accounts of rainfall within the Dry Valleys.[3][4]
The region is one of the world's most extremedeserts, and includes many features includingLake Vida, a saline lake, and theOnyx River, a meltwater stream and Antarctica's longest river. Although no living organisms have been found in thepermafrost here,endolithicphotosynthetic bacteria have been found living in the relatively moist interior of rocks, andanaerobic bacteria, with a metabolism based on iron and sulfur, live under theTaylor Glacier.
The valleys are located within the McMurdo ValleysAntarctic Specially Managed Area (ASMA-2).[5]
The Dry Valleys are so named because of their extremely low humidity and lack of snow or ice cover. They are also dry because, in this location, the mountains are sufficiently high that they block seaward-flowing ice from theEast Antarctic Ice Sheet from reaching theRoss Sea. At 4,800 square kilometres (1,900 sq mi), the valleys constitute around 0.03% of the continent and form the largest ice-free region in Antarctica. The valley floors are covered with loose gravel, in whichice wedgepolygonal patterned ground may be observed.[6]
The unique conditions in the Dry Valleys are caused, in part, bykatabatic winds; these occur when cold, dense air is pulled downhill by the force of gravity. The dry wind evaporates the snow rapidly and little melts into the soil. During the summer, this process can take only hours.
Another important factor is a lack of precipitation. Precipitation averages around 100 millimetres (4 in) per year over a century of records, almost[3][4] exclusively in the form of snow. This contributes to the low humidity of the area.[7]
For several weeks in the summer, the temperature increases enough to allow for glacial melt, which causes small freshwater streams to form.[8] These streams feed the lakes at the base of the valleys, which do not have outflow to the sea, causing them to become highly saline.[citation needed]
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TheMcMurdo Oasis constitutes approximately 4,000 square kilometres (1,500 sq mi) of "deglaciated mountainous desert", according to McKelvey, bounded by the coastline of southVictoria Land and thePolar Plateau. TheTaylor andWright Valleys are major ice-free valleys within theTransantarctic Mountains. These "dry valleys" includehummockymoraines, with frozen lakes, saline ponds, sand dunes, and meltwater streams.Basement rocks include the LatePrecambrian or EarlyPalaeozoic SkeltonGroupmetamorphic rocks, primarily the AsgardFormation, which is a medium-high-grade marble and calcschist. The PalaeozoicGranite Harbourintrusives includegranitoidplutons anddykes, which intruded into the metasedimentary Skelton Group in theLate Cambrian–Early Ordovician during theRoss orogeny. The basement complex is overlain by theJurassicBeacon Supergroup, which is itself intruded byFerrar Dolerite sheets andsills. TheMcMurdo Volcanic Group intrudes, or isinterbedded with, the Taylor and Wright Valleys' moraines asbasalticcinder cones andlava flows. These basalts have ages between 2.1 and 4.4Ma. The Dry Valley Drilling Project (1971–75) determined thePleistocene layer within the Taylor Valley was between 137 and 275 m thick, and composed of interbeddedsandstones, pebbleconglomerates, and laminated siltymudstones. This Pleistocene layerdisconformably overliesPliocene andMiocenediamictites.[9][10]
Endolithicbacteria have been found living in the Dry Valleys, sheltered from the dry air in the relatively moist interior of rocks. Summermeltwater from the glaciers provides the primary source ofsoil nutrients.[11] Scientists consider the Dry Valleys perhaps the closest of any terrestrial environment to the planetMars, and thus an important source of insights into possibleextraterrestrial life.[citation needed]
Anaerobic bacteria whose metabolism is based on iron and sulfur live in sub-freezing temperatures under theTaylor Glacier.
It was previously thought that algae were staining the red ice emerging atBlood Falls but it is now known that the staining is caused by high levels ofiron oxide.[12][13]
Irish and American researchers conducted a field expedition in 2013 toUniversity Valley in order to examine the microbial population and to test a drill designed for sampling on Mars in the permafrost of the driest parts of the valleys, the areas most analogous to the Martian surface. They found no living organisms in the permafrost, the first location on the planet visited by humans with no active microbial life.[14]
In 2014, drones were used in the McMurdo Dry Valleys by a team of scientists fromAuckland University of Technology (AUT) to create baseline maps of the vegetation. In 2015, the New Zealand Antarctic Research Institute granted funding to AUT to develop methods for operatingunmanned aerial vehicles. Over successive summer seasons in Antarctica, the AUT team created three dimensional maps with sub-centimeter resolution, which are now used as baselines.[15]
Part of the Valleys was designated an environmentally protected area in 2004.[citation needed]
From north to south, the three main valleys are
West of Victoria Valley are, from north to south,
Stretching south from Balham Valley are, from west to east:
West of Taylor Valley is
Further south, betweenRoyal Society Range in the west and the west coast ofMcMurdo Sound at the lobe ofKoettlitz Glacier are, from north to south:
Some of the lakes of the Dry Valleys rank among the world's most saline lakes, with a higher salinity thanLake Assal or theDead Sea. The most saline of all is smallDon Juan Pond.
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