Hudson Mountains

The Hudson Mountains are a mountain range in western Ellsworth Land just east of Pine Island Bay at the Walgreen Coast of the Amundsen Sea. They are of volcanic origin, consisting of low scattered mountains and nunataks that protrude through the West Antarctic Ice Sheet. The Hudson Mountains are bounded on the north by Cosgrove Ice Shelf and on the south by Pine Island Glacier. The mountains were volcanically active during the Miocene and Pliocene, but there is evidence for an eruption about two millennia ago and uncertain indications of activity in the 20th century.

Geography and geomorphology
The Hudson Mountains rise in western Ellsworth Land of West Antarctica and were discovered in 1940 by the United States Antarctic Service Expedition. The mountains lie at some distance from the Amundsen Sea's Walgreen Coast, facing Pine Island Bay. The Cosgrove Ice Shelf lies north of the Hudson Mountains. The mountains are remote and visits are rare. In 1991, they were prospected as a potential aircraft landing site.

The mountains are a volcanic field formed by parasitic vents and stratovolcanoes covered in snow and ice, forming a cold desert landscape with an area of about 8400 km2. About 20 mountains emerge above the Antarctic Ice Sheet in the form of nunataks, with the largest rocky outcrops found at Mount Moses and Maish Nunatak. The stratovolcanoes Mount Manthe, Mount Moses, and Teeters Nunatak constitute the bulk of the volcanic field and are heavily eroded. Better preserved are some parasitic cones and volcanic craters which appear to have formed on these three volcanoes. To their south lies the Pine Island Glacier, while the Larter Glacier traverses the Hudson Mountains between Mount Moses and Mount Manthe and other glaciers from the Hudson Mountains join the Pine Island Glacier. The glaciers are rapidly thinning owing to global warming.

Mount Moses reaches an elevation of 749 m above sea level, Teeters Nunatak 617 m, and Mount Manthe 576 m. Other named structures are:
 * Inman Nunatak east-southeast, Meyers Nunatak southeast, Shepherd Dome south, 495 m high Webber Nunatak (which has a crater on its northern side) west and Evans Knoll west-southwest of Mount Manthe; there are additional unnamed features southeast of Inman Nunatak and south/southwest of Webber Nunatak.
 * Mount Moses is almost due north of Mount Manthe; Siren Rock lies far east of Mount Moses, while 536 m high Slusher Nunatak and 574 m high Velie Nunatak are found north of Mount Moses and 232 m high Maish Nunatak southwest of Mount Moses. Unnamed features exist between Maish and Moses and east-northeast from Moses.
 * West-northwest of Mount Moses is the 212 m high Tighe Rock, followed to its north by Hodgson Nunatak and then Teeters Nunatak. To the northwest of Teeters is first an unnamed feature, then Mount Nickens. Northeast of Mount Nickens are Pryor Cliff and Kenfield Nunatak.
 * There may be about three to eleven volcanoes buried under ice in the Hudson Mountains.

The volcanoes are made up by breccia, palagonite tuff, scoriaceous lava flows and tuffs. At Mount Nickles and Mount Moses there are pillow lavas. Lava fragments are dispersed on the slopes of Mount Moses. Volcanic rock sequences that were emplaced under water and under ice are overlaid by volcanic products that were deposed under the atmosphere, there are deposits of volcanic ash and breccia produced by hydromagmatic activity and tuya-like shapes associated with subglacial growth of the volcanoes. At Mount Moses, erosion has exposed dykes. Glaciers have deposited granite boulders and erratic blocks on the Hudson Mountains, and left glacial striations on the pillow lavas of Mount Moses. Physical weathering has yielded soils in some areas. Volcanic glass found in the Pine Island Glacier probably originates in the Hudson Mountains.

Geology
Neighbouring Marie Byrd Land was volcanically active during the Cenozoic, forming a number of volcanoes, some of which are buried under ice, while others emerge above the ice sheet. The Hudson Mountains are part of the Thurston Island or Bellingshausen Volcanic Province, and are its largest and best preserved volcanic field. The volcanism at the mountains may have either been caused by a mantle plume under Marie Byrd Land or by the presence of anomalies (slab windows) in the mantle left over by subduction. Seismic tomography has found evidence of low velocity anomalies under the Hudson Mountains, which may reflect the presence of the Marie Byrd Land mantle plume.

The bedrock around the Hudson Mountains lies below sea level. The basement on which the volcanoes formed is not exposed in the Hudson Mountains, but crops out in the neighbouring Jones Mountains. It forms the so-called Thurston Island tectonic block. Below the Hudson Mountains, the crust is about 21 - 27 km thick. A proposal by Lopatin and Polyakov 1974 is that east and north-trending fractures have controlled the position of the volcanoes.

Composition
The main volcanic rocks include alkali basalt, basalt, hawaiite and tephrite. They define an alkaline suite, some samples trend towards subalkaline. Ultramafic nodules have been reported from some rocks. The magmas erupted by the volcanoes may have originated in a mantle that had been influenced by subduction, and underwent fractionation of olivine as they ascended.

Life and climate
Sparse lichens grow on most of the nunataks, including Usnea species. Mosses have been found growing in gaps between or cracks in boulders. Petrels have been observed. There are no data on the local climate. An automated weather station was installed on Evans Knoll in 2011 and records air temperatures and wind speeds.

Geologic history
The volcanoes were active during the late Miocene and Pliocene. Dates range between 8.5±1.0 and 3.7±0.2 million years ago, an older date is 20±4 million years. There is no evidence of an age progression in any direction.

Ice cover was thicker on the Hudson Mountains during the last glacial maximum, perhaps by about 150 m. Retreat commenced about 14,000-10,000 years ago; however, glaciers were still thicker than today during the early Holocene and deposited rocks on the Hudson Mountains. Another thinning step began about 8,000 years ago and was very fast, perhaps lasting only a century.

Radar data have found a tephra deposit buried under the ice, which may have originated during an eruption of the Hudson Mountains around $207$ BCE; the eruption may correspond to an electrical conductivity anomaly in an ice core at Siple Dome and a tephra layer dated to 325 BCE in the Byrd Station ice core. The eruption may have had a volcanic explosivity index of 3-4 and originated in an area east of the main Hudson Mountains. LeMasurier et al. 1990 referenced reports of activity in the Hudson Mountains. These include a report of steaming at one of the nunataks and of satellite data of a potential eruption in 1985 of Webber Nunatak, but the report of this eruption is questionable. There is no evidence of increased heat flow or morphological changes at Webber Nunatak since then, but anomalies in helium isotope ratios from the Pine Island Glacier ice have been attributed to volcanic activity in the Hudson Mountains.

Named features
The southern part of the mountains includes, from west to east, Evans Knoll, Webber Nunatak, Shepherd Dome, Mount Manthe, Inman Nunatak, Meyers Nunatak and Wold Nunatak. The central part includes, from west to east, Tighe Rock, Maish Nunatak, Mount Moses, Velie Nunatak, Slusher Nunatak and Siren Rock. Features to the north, from south to north, include Hodgson Nunatak, Teeters Nunatak, Mount Nickens, Pryor Cliff and Kenfield Nunatak.

Evans Knoll
-74.85°N, -100.41667°W. A mainly snow-covered knoll on the coast at the north side of the terminus of Pine Island Glacier. It lies 9 nmi southwest of Webber Nunatak and marks the southwest end of the Hudson Mountains. Mapped from air photos taken by United States Navy OpHjp, 1946-47. Named by US-ACAN for Donald J. Evans who studied very-lowfrequency emissions from the upper atmosphere at Byrd Station,1960-61.

Webber Nunatak
-74.78333°N, -99.83333°W. A nunatak 495 m high standing 6 nmi west of Mount Manthe. Mapped from air photos taken by United States Navy Operation Highjump (OpHjp), 1946–47. Named by US-ACAN for George E. Webber, electrical engineer at Byrd Station, 1967.

Shepherd Dome
-74.86667°N, -99.55°W. A low dome-shaped mountain at the north side of Pine Island Glacier, standing 4 nmi southwest of Mount Manthe. Mapped from air photos made by United States Navy OpHjp, 1946-47. Named by US-ACAN for Donald C. Shepherd, ionospheric physicist at Byrd Station, 1967.

Mount Manthe
-74.78333°N, -99.35°W. A mountain 575 m high standing 5 nmi north-northeast of Shepherd Dome, in the south part of the Hudson Mountains. Mapped from air photos taken by United States Navy OpHjp, 1946-47. Named by US-ACAN for Lawrene L. Manthe, meteorologist at Byrd Station, 1967.

Inman Nunatak
-74.81667°N, -98.9°W. A nunatak standing 6 nmi east of Mount Manthe in the southeast part of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Martin M. Inman, auroral scientist at Byrd Station, 1960–61 and 1961-62 seasons.

Meyers Nunatak
-74.9°N, -98.76667°W. A nunatak located 10 nmi east-southeast of Mount Manthe, at the southeast end of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Herbert Meyers, USARP geomagnetist at Byrd Station, 1960-61.

Wold Nunatak
-74.78333°N, -98.63333°W. A nunatak standing 10 nmi east of Mount Manthe in the southeast  part of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Richard J. Wold, USARP geologist at Byrd Station, 1960-61 season.

Koehler Nunatak
-74.86667°N, -98.13333°W. Isolated nunatak about 20 nmi east-southeast of Mount Manthe, at the southeast  margin of the Hudson Mountains. Mapped by USGS from ground surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Walter Koehler, United States Army Aviation Detachment, helicopter pilot for the Ellsworth Land Survey, 1968-69.

Tighe Rock
-74.43333°N, -100.06667°W. A rock outcropping along the coastal slope at the west margin of the Hudson Mountains, located 15 nmi northwest of Mount Moses. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Robert F. Tighe, electrical engineer at Byrd Station, 1964-65.

Maish Nunatak
-74.6°N, -99.46667°W. A nunatak located 5 nmi west-southwest of Mount Moses, in the central part of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for F. Michael Maish, ionospheric physicist at Byrd Station in 1967, who served as United States exchange scientist at Vostok Station in 1969.

Mount Moses
-74.55°N, -99.18333°W. The highest 750 m high and most prominent of the Hudson Mountains, located near the center of the group, about 14 nmi north-northeast of Mount Manthe. Mapped from air photos taken by United States Navy OpHjp, 1946–47. Named by US-ACAN for Robert L. Moses, geomagnetist-seismologist at Byrd Station, 1967.

Dean Nunataks
-74.51667°N, -98.8°W. Two nunataks lying about 6 nmi east-northeast of Mount Moses. Mapped by USGS from ground surveys and United States Navy air photos, 1960-66. Named by US-ACAN for William S. Dean of Pleasanton, Texas, who served as ham radio contact in the United States for the Ellsworth Land Survey party of 1968-69, and for other USARP field parties over a three year period.

Velie Nunatak
-74.38333°N, -99.16667°W. A nunatak located 9 nmi north of Mount Moses. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-AC AN for Edward C. Velie, meteorologist at Byrd Station, 1967.

Slusher Nunatak
-74.45°N, -99.1°W. A nunatak lying 5 nmi north of Mount Moses. Mapped from air photos taken by United States Navy OpHjp, 1946-47. Named by US-ACAN for Harold E. Slusher, meteorologist at Byrd Station, 1967.

Siren Rock
-74.55°N, -98.4°W. A fairly isolated rock lying 12 nmi east of-Mount Moses, in the east  part of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Jan C. Siren, radio scientist at Byrd Station, 1967.

Hodgson Nunatak
-74.28333°N, -100.06667°W. A nunatak which lies 5 nmi south of Teeters Nunatak and 20 nmi northwest of Mount Moses. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Ronald A. Hodgson, United States Navy, builder with the Byrd Station party, 1966.

Teeters Nunata
-74.2°N, -100.01667°W. A nunatak 615 m high standing 5 nmi north of Hodgson Nunatak. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Robert E. Teeters, United States Navy, storekeeper at Byrd Station, 1966.

Rebholz Nunatak
-74.08333°N, -100.21667°W. Isolated nunatak just north of the Hudson Mountains, located 8 nmi north-northwest of Teeters Nunatak. Mapped by USGS from ground surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Major Edward Rebholz, operations officer of the United States Army Aviation Detachment which supported the Ellsworth Land Survey, 1968-69.

Mount Nickens
-73.93333°N, -100.33333°W. A snow-covered mesa-type mountain with a steep northern rock face, marking the northwest extremity of the Hudson Mountains. It stands just east of the base of Canisteo Peninsula and overlooks Cosgrove Ice Shelf. Mapped from air photos taken by United States Navy OpHjp, 1946-47. Named by US-ACAN for Herbert P. Nickens, map compilation specialist who contributed significantly to the construction of USGS sketch maps of Antarctica.

Pryor Cliff
-73.88333°N, -100°W. A distinctive rock cliff which faces northward toward Cosgrove Ice Shelf, standing 5 nmi northeast of Mount Nickens at the north end of the Hudson Mountains. Mapped by USGS from surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Douglas A. Pryor, map compilation specialist who contributed significantly to construction of USGS sketch maps of Antarctica.

Kenfield Nunatak
-73.76667°N, -99.05°W. An isolated nunatak which lies about 8 nmi southeast of the head of Cosgrove Ice Shelf and 17 nmi east-northeast  of Pryor Cliff, at the extreme north end of the Hudson Mountains. Mapped by USGS from ground surveys and United States Navy air photos, 1960-66. Named by US-ACAN for Richard E. Kenfield, USGS topographic engineer working from Byrd Station in the 1963-64 season.