McMurdo Dry Valleys

imagery acquired on December 18, 1999 The Dry Valleys are one of the most extreme habitats on Earth, and are classified as a cold desert. At approximately , the valleys constitute around 0.03% of the continent and form the largest ice-free region in Antarctica. The region's low precipitation is the result of the snow shadow that is created from the Transantarctic Mountains the valleys are situated in; the highest peaks in the region are some . As a result, much of the valley floors remain exposed and covered with loose gravel, in which ice wedge polygonal patterned ground may be observed. The unique conditions in the Dry Valleys are caused, in part, by katabatic 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 per year over a century of records, almost Despite a notable lack of precipitation or surface-level ice, the Dry Valley region is home to over 6000 lakes and ponds. For several weeks in the summer, the temperature increases enough to allow for glacial melt, which causes small freshwater streams to form. 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. The maximum and minimum air temperatures recorded in the McMurdo Dry Valleys (MDVs) were at Taylor Glacier and at Lake Vida, respectively. The mean annual air temperature on the valleys floors ranged between at Lake Bonney to at Lake Vida. Within Taylor Valley, which has eight stations, the valley bottom mean annual temperatures ranged from to , in contrast to the four glaciers stations that ranged from to . High elevation sites ranged from to . The order of mean annual temperatures among the valleys, using valley bottom stations, warmest to coldest is Miers Valley , Taylor Valley , Wright Valley and Victoria Valley . ==Geology==

The McMurdo Oasis is bounded by the coastline of south Victoria Land and the Polar Plateau. The Taylor and Wright Valleys are major ice-free valleys within the Transantarctic Mountains. These "dry valleys" include hummocky moraines, with frozen lakes, saline ponds, sand dunes, and meltwater streams. Basement rocks include the Late Precambrian or Early Palaeozoic Skelton Group metamorphic rocks, primarily the Asgard Formation, which is a medium-high-grade marble and calc schist. The Palaeozoic Granite Harbour intrusives include granitoid plutons and dykes, which intruded into the metasedimentary Skelton Group in the Late Cambrian–Early Ordovician during the Ross orogeny. The basement complex is overlain by the Jurassic Beacon Supergroup, which is itself intruded by Ferrar Dolerite sheets and sills. The McMurdo Volcanic Group intrudes, or is interbedded with, the Taylor and Wright Valleys' moraines as basaltic cinder cones and lava flows. These basalts have ages between 2.1 and 4.4 Ma. The Dry Valley Drilling Project (1971–75) determined the Pleistocene layer within the Taylor Valley was between 137 and 275 m thick, and composed of interbedded sandstones, pebble conglomerates, and laminated silty mudstones. This Pleistocene layer disconformably overlies Pliocene and Miocene diamictites. ==Research==

seal carcass|thumb Since the Valleys' discovery in the early 1900s and the establishment of McMurdo Station (United States) and Scott Base (New Zealand) as research stations on nearby Ross Island in the 1950s, the Dry Valleys region has been extensively studied by scientists. The valleys' hyper-arid, cold-desert climate was soon identified as a high-fidelity terrestrial analogue for the environment of Mars, and geologists and astrophysicists have subsequently used the Valleys as a testing ground for analog-based studies since NASA's Viking Program in the 1970s. In 1985, the first continuously operating meteorological station was installed at Lake Hoare, and in 1992, Taylor Valley, the southernmost of the three major Dry Valleys, was selected as a National Science Foundation Long Term Ecological Research (LTER) site, enabling for long-term scientific investigation of ecological processes over decadal timescales. , there are a total of 26 real-time meteorological stations, stream gauges, and observing platforms and a total of 1028 unique scientific publications affiliated or supported by the LTER program. Irish and American researchers conducted a field expedition in 2013 to University 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, making University Valley the first location on the planet visited by humans with no detected active microbial life. Similarly, much research has been done on analyzing the various ice-covered lakes and streams in the valleys. The lakes are unique physically due to a climate-induced balance between the maintenance of a thick, permanent ice cover due to low temperatures, the loss of ice to sublimation, and the replacement of water into the lakes themselves from seasonal glacial meltwater inflow. Research has discovered the presence of microbial mats along glacial-melt streams, lakes, wetlands, and ice in the region. Dry Valley microbial mats are unique due to the constant scouring from katabatic winds. Endolithic bacteria have been found living in the Dry Valleys, sheltered from the dry air in the relatively moist interior of rocks. Summer meltwater from the glaciers provides the primary source of soil nutrients. Anaerobic bacteria whose metabolism is based on iron and sulfur live in sub-freezing temperatures under the Taylor Glacier. It was previously thought that algae were staining the red ice emerging at Blood Falls, but it is now known that the staining is caused by high levels of iron oxide. In 2014, drones were used in the McMurdo Dry Valleys by a team of scientists from Auckland 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 operating unmanned 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. Part of the Valleys was designated an environmentally protected area in 2004. ==Major geographic features==

Valleys • Alatna Valley (sometimes incorrectly spelled Atlanta Valley) is the northernmost, north of Benson Glacier. From north to south, the three main valleys are • Victoria Valley (between St. Johns Range in the north and Olympus Range in the south) • Wright Valley (between Olympus Range in the north and Asgard Range in the south) • Taylor Valley (between Asgard Range in the north and Kukri Hills in the south) West of Victoria Valley are, from north to south, • Barwick Valley • Balham Valley • McKelvey Valley Stretching south from Balham Valley are, from west to east: • Priscu Valley • Wall Valley • Virginia Valley • Stuiver Valley West of Taylor Valley is • Pearse Valley (sometimes incorrectly spelled Pearce Valley). Further south, between Royal Society Range in the west and the west coast of McMurdo Sound at the lobe of Koettlitz Glacier are, from north to south: • Garwood Valley • Marshall Valley • Miers Valley Glaciers • Clark Wright Valley • Wright Upper • Wright Lower Taylor Valley • Rhone • Suess • Hughes • Taylor • Canada • Commonwealth • Howard • Doran Lakes Some of the lakes of the Dry Valleys rank among the world's most saline lakes, with a higher salinity than Lake Assal or the Dead Sea. The most saline of all is small Don Juan Pond. • Lake Vida (Victoria Valley) • Lake Thomas (Victoria Valley) • Lake Vanda (Wright Valley) • Lake Brownworth (Wright Valley) (freshwater) • Don Juan Pond (Wright Valley) • Lake Fryxell (Taylor Valley) • Lake Hoare (Taylor Valley) • Lake Chad (Taylor Valley) • Parera Pond (Taylor Valley) (freshwater) • Lake Bonney (Taylor Valley) • Lake Joyce (Pearse Valley) • Lake Garwood (Garwood Valley) • Lake Miers (Miers Valley) Former lakes • Lake Washburn (Taylor Valley) Rivers • Kite Stream (Victoria Valley) • Onyx River (Wright Valley) • Doran Stream (Taylor Valley) • Vincent Creek (Taylor Valley) • Crescent Stream (Taylor Valley) • Harnish Creek (Taylor Valley) • Huey Creek (Taylor Valley) • Lost Seal Stream (Taylor Valley) Other • Blood Falls, a feature caused by iron oxide causing a coloured water outflow from Taylor Glacier into West Lake Bonney • Gargoyle Ridge, a ridge of eroded exposed rocks in Wright Valley • Airdevronsix Icefalls, a set of icefalls at the head of Wright Upper Glacier • Battleship Promontory, a sandstone promontory in Alatna Valley ==See also==