Mount Moulton

Mount Moulton is a complex of ice-covered shield volcanoes, standing east of Mount Berlin in the Flood Range, Marie Byrd Land, Antarctica. It is named for Richard S. Moulton, chief dog driver at West Base. The volcano is of Pliocene age and is presently inactive.

The Prahl Crags are located on the southern slopes of Mount Moulton and are part of a caldera. There, an exposed area of blue ice can be found; this ice contains tephra layers from mainly neighbouring Mount Berlin volcano and some of the ice is almost half a million years old.

Geology and geomorphology

Mount Moulton lies in Marie Byrd LandTemplate:Sfn of Western Antarctica and in the region of the West Antarctic Ice Sheet. It is part of a system of volcanoes including Mount Berlin, Mount Takahe and Mount Waesche as well as of recently active subglacial volcanism.Template:Sfn The volcano is named for Richard S. Moulton, chief dog driver of the United States Antarctic Service Expedition;Template:Sfn the western end of the Flood RangeTemplate:Sfn where Mount Moulton lies was visited by this expedition in December 1940.Template:Sfn Other field expeditions took place in 1967–1968, 1977–1978, 1993-1994 and 1999–2000.Template:Sfn

File:MountMoultonMap.jpg

Topographic map of Mounts Moulton and Berlin

The volcano appears to be of Pliocene ageTemplate:Sfn and there is no evidence that it was glaciated during its eruptions.Template:Sfn Only a few outcrops of Mount Moulton have been dated and these yield ages of 5.3 million years,Template:Sfn with further age estimates of 4.9 – 4.7 million years ago,Template:Sfn 5.9 million years agoTemplate:Sfn and 1.04 ± 0.04 million years agoTemplate:Sfn at Gawne Nunatak,Template:Sfn which is a parasitic cone.Template:Sfn There is no evidence of eruptive or thermal activity unlike at its neighbourTemplate:Sfn Mount Berlin.Template:Sfn Earthquakes have been recorded at Mount Moulton and are either of volcano-tectonic origin or due to the movement of ice along the flanks of the volcano.

The mountain is high,Template:Sfn rising about above the ice surface on its northern flank,Template:Sfn and located within the Flood Range; Mount Berlin lies across the c. wide, high-elevationTemplate:Sfn Wells SaddleTemplate:Sfn to the west and Kohler Dome is east of Moulton.Template:Sfn Even farther east lie Mount Bursey, Mount Andrus, Mount Kosciuszko and Mount Kauffman, in the Ames Range. Mount Moulton is an obstacle to ice flow in the West Antarctic Ice Sheet, which has piled up on the mountain and is about higher on the upstream side.Template:Sfn

Mount Moulton is formed by a complex of glaciated but largely unerodedTemplate:Sfn shield volcanoesTemplate:Sfn with two or possibly threeTemplate:Sfn ice-filled calderas,Template:Sfn each of which is about wide.Template:Sfn The calderas are apartTemplate:Sfn and located at the Prahl Crags, Britt Peak and potentially Kohler Dome localities.Template:Sfn Additionally the Prahl Crags – remnants of the former caldera rim – are found south, Gawne Nunatak west, Edwards Spur northeast and the Moulton Icefalls on the northern side of the mountain.Template:Sfn The total volume of the complex is about ,Template:Sfn comparable to that of Mount Shasta in the Cascade Range, and is one of the largest volcanoes in the Flood Range and Ames Range.Template:Sfn Only the western part of the Mount Moulton emerges from the ice.

Volcanic rocks found at Mount Moulton include pantellerite,Template:Sfn phonoliteTemplate:Sfn and trachyte;Template:Sfn phenocryst phases found in the pantellerite include aenigmatite, anorthoclase, fayalite, hedenbergite, ilmenite and quartz.Template:Sfn

Blue ice field

A blue ice field has formed within the caldera of Mount Moulton behind the Prahl Crags, and contains ice almost 500,000 years old.Template:Sfn It is the oldest dated ice in West AntarcticaTemplate:Sfn and much older than ice found elsewhere in West Antarctic ice cores.Template:Sfn Such blue ice fields like those found at Mount Moulton form when glaciers run into an obstacle – in this case the Prahl Crags – and part of the ice starts moving vertically as it undergoes ablation processes like sublimation.Template:Sfn In the case of Mount Moulton, this outcrop of ice is about long.Template:Sfn The ice has been used to reconstruct past climate states in West Antarctica, including the beginning and end of the last interglacial,Template:Sfn and shows evidence that the West Antarctic Ice Sheet collapsed during that interglacial.

In addition, recognizable tephra layers are found in this iceTemplate:Sfn and appear to originate from explosive eruptions of volcanoes such as Mount Berlin, Mount Takahe and Mount Waesche,Template:Sfn although some may come from parasitic vents of Mount Berlin and Mount Moulton.Template:Sfn These tephra layers at Mount Moulton crop out in parallel layersTemplate:Sfn and geochemical traits indicate an origin at Mount Berlin although some layers may have been erupted from mafic volcanoes at Mount Moulton and Mount Berlin.Template:Sfn Furthermore, the appearance of the deposits indicates that the eruptions of Mount Berlin were highly explosive.Template:Sfn Most likely they eventually fell onto the ice of Mount Moulton, were incorporated in it and then transported downward to the blue ice field.Template:Sfn

See also

• List of volcanoes in Antarctica

Further reading

• Template:Gnis