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SPRI Physical Sciences Seminar Series 2008-9

SPRI Physical Sciences Seminar Series 2008-9

Michaelmas Term 2008-9

Wednesday 15th October
Murray Mitchell
Antarctic Engineering
Structural engineering in Antarctica presents unique technical and logistical challenges. With more than twenty-five years of experience, Murray Mitchell has been the lead structural engineer in New Zealand's Antarctic programme. Projects include rebuilding of the Scott Base, structural assessments of Scott's and Shackleton's huts and wind turbines for Arrival Heights. This illustrated talk will focus on the technical challenges of ANDRILL , an international Antarctic drilling project where sedimentary cores are collected from beneath moving ice. The talk will also outline some of the general engineering techniques that New Zealand has utilised in one of the world's most extreme environments.
Wednesday 29th October [please note change in speaker & topic]
Kelly Hogan (University of Cambridge)
Late Quaternary submarine landform assemblages and former ice flow of the Svalbard-Barents Sea Ice Sheet, east of Svalbard
Geophysical and geological data from the seafloor around Kong Karls Land and the northern Barents Sea Shelf reveal a variety of subglacial, ice marginal and proglacial bedforms that were produced when grounded ice last expanded and retreated in the area. The spatial arrangement of both flow-parallel (subglacial) bedforms and flow-transverse (ice-marginal) bedforms indicate that ice flow was to the east/northeast in bathymetric depressions around the archipelago and probably fed into the larger Franz Victoria Trough. In the Kvitøya Trough ice flow was to the north. The form, type and discontinuity of streamlined bedforms indicates that these depressions were not filled with fast-flowing ice streams sensu stricto, although elevated ice flow velocities did occur. Landform assemblages characterise the glacial evolution of this margin. Subglacial assemblages suggest that up to two ice flow phases occurred, with grounded ice advancing across a variety of seafloor substrates. Ice marginal assemblages suggest that retreat from the outer shelf was rapid although retreat was slower/punctuated as ice reached the shallow parts of bathymetric depressions. During deglaciation, temporary calving bays were established and facilitated rapid ice loss through calving. Reconstructions of the former Svalbard-Barents Sea Ice Sheet derived from these data are significantly different from previous regional reconstructions (e.g. Landvik et al., 1998; Svendsen et al., 2004). This area is particularly important for understanding the history of the margin as regional uplift data and numerical modelling place the former ice sheet centre just east/southeast of Kongs Karls Land.
Wednesday 12 November
Adrian Luckman (Swansea University)
Greenland Ice Sheet dynamics and drivers
This talk will review the recent fast-paced developments in our knowledge of the dynamics of Greenland glaciers and what influences the rates of flow. The role of satellite remote sensing in understanding surface melt patterns, surface flow rate and ice front geometry will be explained. The current conditions at Kangerdlugssuaq and Helheim glaciers will be brought up to date.
Wednesday 26 November
Robert Bingham (British Antarctic Survey)
In situ glacial geophysical investigations of Pine Island Glacier, West Antarctica
Remote sensing observations since the 1990s have exposed Pine Island Glacier as one of the most rapidly thinning and accelerating ice streams in Antarctica, and therefore the world. Flowing into the Amundsen Sea Embayment, thought to be an area of potential ocean warming, and grounded well below isostatically-rebounded sea levels, there is concern that the astonishing changes witnessed across the region from space reflect the onset of a major response of the West Antarctic Ice Sheet to global warming. Attempts to model the behaviour of the ice sheet in this region have been hindered by a dearth of subsurface information, with fieldwork hampered by the extreme remoteness of the catchment. This talk will report on the first in situ glacial geophysical investigations ever conducted on Pine Island Glacier. Punctuated with photographic material from the speaker's first visit to the continent, the talk will outline the range of geophysical methods used to investigate change across this extremely remote, yet highly dynamic region; and will focus on the use of oversnow radar to image the internal and basal conditions beneath the surface of Pine Island Glacier.

Lent Term 2008-9

Wednesday 18 February 2009
Clive Oppenheimer, University of Cambridge
Erebus volcano, Antarctica: eruption dynamics and atmospheric impacts
Erebus is an exceptional volcano. It rises nearly 4 km above sea-level, dominating Ross Island, and continuously erupts an unusual magma (phonolite) via a persistent lava lake in the summit crater. But it also goes through phases, lasting months, in which this peaceful behaviour is punctuated by violent explosive eruptions that occur a few times a day. Erebus also represents the largest point source of several reactive gases and particles to the Antarctic troposphere. The volcano is monitored more or less year-round by a network of seismometers and other instruments, and is subject to intense field campaigns each year during the austral summer. Drawing on the results of measurements of gas and heat emissions from the volcano, I will review progress in the development of conceptual models for the evolution, transport and degassing of magma beneath Erebus, discuss the origins of the explosive activity, and examine the evidence for impacts of the emissions of NOx, halogens and sulfur on the atmospheric environment.
Wednesday 4 March 2009
John Woodward, Northumbria University
Geophysical surveys of Subglacial Lake Ellsworth, West Antarctica: implications for in-situ exploration.
In addition to exerting a significant impact on ice sheet dynamics, subglacial lakes are expected to contain unique life forms and records of ice sheet history. To date, none of the ~150 Antarctic lakes discovered from radio echo sounding surveys have been accessed directly. The Ellsworth Consortium has recently received funding to access Subglacial Lake Ellsworth (SLE) in West Antarctica in 2012/13. In order to plan for lake access we have completed a geophysical reconnaissance of SLE. A series of airborne and ground-based radar surveys have mapped: a) the lake outline, b) the ice thickness in the region and c) the internal structure of the ice sheet. Radar surveys reveal that SLE lies beneath 3.2 km of ice in a deep, topographically controlled fjord-like valley, is 11.9 km long and has a maximum width of 2.9 km. Between November 2007 and February 2008 five seismic reflection survey lines were collected perpendicular to the long axis of the lake at 1.4 km intervals. The seismic profiles show the steep valley side-walls, lake water depths and the morphology and composition of the lakebed. The seismic profiles indicate that the thickness of the water-body increases down-lake from a maximum depth of 50 m on the up-flow profile to a maximum depth of nearly 160 m on the down-flow profile, producing a water volume of 1.4 km3, suggesting that SLE is a substantial body of water. The lake bed is composed of high-porosity, low-density sediments with acoustic properties very similar to material found on the deep ocean floor. Seismic reflections indicate a substantial thickness of this soft sedimentary material, accumulated at the lake bed in a low-energy environment. Modelled basal mass balance suggests that nearly 80% of the ice water interface is at the melting point. A thin 15 m thickness of accretion ice forms at the down-ice-flow end of the lake. Geophysical results confirm that SLE is an ideal target for in situ sampling and indicate significant practical implications for the lake access operation.

Easter Term 2008-9

Wednesday 22nd April, 16:30 - 17:30
Jason Gulley (Department of Geological Sciences, University of Florida)
Mechanisms of englacial conduit formation and their implications for subglacial recharge
Ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by Shreve (1972). The Shreve model is based on three main assumptions: (1) englacial drainage is in steady state; (2) englacial water will flow along the steepest hydraulic gradient within the glacier; and (3) pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls. The Shreve model has been widely adopted as a fundamental component of englacial drainage theory.
To evaluate Shreve's theory, we used speleological techniques to directly survey englacial conduits. We have explored more than 45 distinct englacial conduits to ice depths of 110 m and mapped a total of 9.5 km of passage in 28 conduits in temperate, polythermal, cold-based and debris-covered glaciers between 2005 and 2009. New information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 203 m using speleological techniques. In all cases, englacial drainage systems consisted of a single unbranching conduit. Englacial conduit morphologies were found to be intimately linked to the orientation of a glacier's principal stresses or the presence of pre-existing lines of high hydraulic conductivity. If a sufficient supply of water is available, hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive. On unfractured glacier surfaces, relatively shallow subhorizontal conduits with migrating nickpoints form by cut-and-closure provided channel incision is significantly faster than surface lowering. Conduits can also form along permeable debris-filled crevasse traces that connect supraglacial lake basins of different potential. Only conduits formed by extensional hydrofracture were found to be connected to glacier beds. Our results suggest that a Shreve-type englacial drainage system probably does not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed of the Greenland Ice Sheet where supraglacial water bodies either intersect, or are advected through, zones of acceleration.
Wednesday 20th May, 16:30 - 17:30
Chris Woodworth-Lynas (NW Atlantic Ocean Observing System Partnership)
Where Have All the Icebergs Gone?
The Greenland Ice Sheet is annually producing nearly 50% more icebergs, volumetrically, than it did prior to 1995. This volumetric increase should be reflected in a similar increase in the numbers of icebergs. However, the increase in numbers is not seen along the iceberg drift route further south on the Grand Banks of Newfoundland. The presentation examines the reasons for this unanticipated and massive increase in iceberg production into the NW Atlantic and discusses possible reasons why the increase is not seen further south.