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Topic Name: BAS Scientists for the First Time Find Under-Ice Volcanic Eruption in Antarctica Using Airborne Ice-Sounding Radar

Category: Geo sciences & technology

Research persons: Hugh Corr, Professor David Vaughan

Location: British Antarctic Survey (BAS), United Kingdom

Details

The first evidence of a volcanic eruption from beneath Antarctica’s most rapidly changing ice sheet is reported this week in the journal Nature Geosciences. The volcano on the West Antarctic Ice Sheet erupted 2000 years ago (325BC) and remains active.

Using airborne ice-sounding radar, scientists from British Antarctic Survey (BAS) discovered a layer of ash produced by a ‘subglacial’ volcano. It extends across an area larger than Wales.

Lead author, Hugh Corr of the BAS says, “The discovery of a ‘subglacial’ volcanic eruption from beneath the Antarctic ice sheet is unique in itself. But our techniques also allow us to put a date on the eruption, determine how powerful it was and map out the area where ash fell. We believe this was the biggest eruption in Antarctica during the last 10,000 years. It blew a substantial hole in the ice sheet, and generated a plume of ash and gas that rose around 12 km into air.”

The discovery is another vital piece of evidence that will help determine the future of the West Antarctic Ice Sheet and refine predictions of future sea-level rise. Co-author Professor David Vaughan (BAS) says,

“This eruption occurred close to Pine Island Glacier on the West Antarctic Ice Sheet. The flow of this glacier towards the coast has speeded up in recent decades and it may be possible that heat from the volcano has caused some of that acceleration. However, it cannot explain the more widespread thinning of West Antarctic glaciers that together are contributing nearly 0.2mm per year to sea-level rise. This wider change most probably has its origin in warming ocean waters.”

Note for West Antarctic Ice Sheet
The West Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West (or Lesser) Antarctica, the portion of Antarctica west of the Transantarctic Mountains. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.
It is estimated that the volume of the Antarctic ice sheet is about 25.4 million km3, and the WAIS contains just under 10% of this, or 2.2 million km3. This enormous weight has caused the underlying rock to sink by between 0.5 and 1 kilometres in a process known as isostatic depression.
Under the massive forces of their own weight, the ice sheets deform and drag themselves outward. The interior ice flows slowly over rough bedrock. Away from the interior, the ice is channelled into ice streams, transporting ice from the center of the continent to the sea. These streams are separated by slow-flowing ice ridges. The inter-stream ridges are frozen to the bed while the bed beneath the ice streams consists of water-saturated clay. The clay was deposited before the ice sheet occupied the region, when much of West Antarctica was a marine seaway. The rapid ice-stream flow is due to the water-saturated clay.
When ice streams finally reach the coast and push out across the ocean, they pass over rocky terrain, anchoring themselves to the irregular rocks to form a hinge. The ice will continue to grow outward onto the water. The result is a large, floating shelf of ice affixed to the continent.

Note for Glacier
A glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water. Glaciers cover vast areas of polar regions but are restricted to the highest mountains in the tropics. Elsewhere in the solar system, the vast polar ice caps of Mars rival those of the Earth.
Many geologic processes are interrupted or modified significantly by glaciers. Geologic features created by glaciers include end, lateral, ground and medial moraines that form from glacially transported rocks and debris; U-shaped valleys and cirques at their heads, and the glacier fringe, which is the area where the glacier has recently melted into water. Much precipitation becomes trapped in the glaciers instead of flowing immediately back to the oceans, causing sea level drops and greatly modifying the hydrology of streams. The Earth's crust is pushed down by the weight of the ice, and meltwater commonly collects and forms lakes along the ice margins.

The subglacial volcano has a ’volcanic explosion index’ of around 3-4. Heat from the volcano creates melt-water that lubricates the base of the ice sheet and increases the flow towards the sea.

Pine Island Glacier on the West Antarctic Ice Sheet is showing rapid change and BAS scientists are part of an international research effort to understand this change.

Glaciers are like massive rivers of ice that flow towards the coast and discharge icebergs into the sea.

Since the 1970’s scientists have used radar, seismic and satellite technologies to discover a number of features – including lakes – hidden beneath the ice.

The volcano is located beneath the West Antarctic ice sheet in the Hudson Mountains at latitude 74.6°South, longitude 97°West. Volcanoes are an important component of the Antarctic region. They formed in diverse tectonic settings, mainly as a result of mantle plumes acting on the stationary Antarctic plate. The region also includes amongst the world's best examples of a long-lived continental margin arc (Antarctic Peninsula), a very young marginal basin (Bransfield Strait) and an oceanic island arc (South Sandwich Islands). Many extinct volcanoes are very well preserved and others are still active (e.g. Deception Island, Mount Erebus, and the South Sandwich Islands). Volcanic eruptions were common during the past 25 million years, and coincided with the great period of climatic deterioration that resulted in the formation of the Antarctic ice sheet. Many of the volcanoes show the effects of interaction with ice. BAS has played a major role in describing these effects and modelling their influences on the resulting volcanic sequences. It is important to describe and understand these interactions in geologically recent times in order to predict future configurations of the ice sheet and its role in the global system.

In figure 1, BAS Twin Otter in flight during the aerial survey

In figure 2, Team photo from the Hudson Mountain survey flight season. Hugh Corr is centre foreground - lying, Prof David Vaughan is directly behind him. Pilot David Leatherdale is in blue in the back row behind David Vaughan.

In figure 3, British Antarctic Survey Twin Otter taking off with full survey fit. The plane is fitted with 8 radar antennas and magnetometer pods for this research.

In figure 4, BAS Twin Otter in flight during the aerial survey