%0 Journal Article
%J Geophysical Research Letters
%D 2013
%T Rapid Submarine Melting Driven by Subglacial Discharge, LeConte Glacier, Alaska
%A Roman J. Motyka
%A Dryer, W. P.
%A Jason M Amundson
%A Martin Truffer
%A Mark Fahnestock
%K frontal ablation
%K submarine melting
%K tidewater glaciers
%X We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted 4 days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d−1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff.
%B Geophysical Research Letters
%V 40
%G eng
%U http://dx.doi.org/10.1002/grl.51011
%R 10.1002/grl.51011
%0 Journal Article
%J Journal of Geophysical Research: Oceans
%D 2013
%T On the seasonal freshwater stratification in the proximity of fast-flowing tidewater outlet glaciers in a sub-Arctic sill fjord
%A Mortensen, J.
%A Bendtsen, J.
%A Roman J. Motyka
%A Lennert, K.
%A Martin Truffer
%A Mark Fahnestock
%A Rysgaard, S.
%K fjord
%K freshwater sources and their distribution
%K Greenland Ice Sheet
%K subglacial freshwater fraction model
%K subsurface heat sources for glacial ice melt
%K tidewater outlet glaciers
%X The Greenland Ice Sheet releases large amounts of freshwater into the fjords around Greenland and many fjords are in direct contact with the ice sheet through tidewater outlet glaciers. Here we present the first seasonal hydrographic observations from the inner part of a sub-Arctic fjord, relatively close to and within 4–50 km of a fast-flowing tidewater outlet glacier. This region is characterized by a dense glacial and sea ice cover. Freshwater from runoff, subglacial freshwater (SgFW) discharge, glacial, and sea ice melt are observed above 50–90 m depth. During summer, SgFW and subsurface glacial melt mixed with ambient water are observed as a layered structure in the temperature profiles below the low-saline summer surface layer (<7 m). During winter, the upper water column is characterized by stepwise halo- and thermoclines formed by mixing between deeper layers and the surface layer influenced by ice melt. The warm (T > 1°C) intermediate water mass is a significant subsurface heat source for ice melt. We analyze the temperature and salinity profiles observed in late summer with a thermodynamic mixing model and determine the total freshwater content in the layer below the summer surface layer to be between 5% and 11%. The total freshwater contribution in this layer from melted glacial ice was estimated to be 1–2%, while the corresponding SgFW was estimated to be 3–10%. The winter measurements in the subsurface halocline layer showed a total freshwater content of about 1% and no significant contribution from SgFW.
%B Journal of Geophysical Research: Oceans
%V 118
%P 1382–1395
%G eng
%U http://dx.doi.org/10.1002/jgrc.20134
%R 10.1002/jgrc.20134
%0 Journal Article
%J Journal of Geophysical Research
%D 2012
%T Gravity and uplift rates observed in southeast Alaska and their comparison with GIA model predictions
%A Tatsuru Sato
%A Miura, S.
%A Sun, W.
%A Sugano, T.
%A Jeffrey T. Freymueller
%A Chris F. Larsen
%A Ohta, Y.
%A Fujimoto, H.
%A Inazu, D.
%A Roman J. Motyka
%B Journal of Geophysical Research
%V 117
%P B01401
%G eng
%0 Journal Article
%J Eos, Transactions American Geophysical Union
%D 2011
%T A complex relationship between calving glaciers and climate
%A Post, Austin
%A Shad OʼNeel
%A Roman J. Motyka
%A Streveler, Gregory
%K climate
%K glaciers
%X Many terrestrial glaciers are sensitive indicators of past and present climate change as atmospheric temperature and snowfall modulate glacier volume. However, climate interpretations based on glacier behavior require careful selection of representative glaciers, as was recently pointed out for surging and debris-covered glaciers, whose behavior often defies regional glacier response to climate [Yde and Paasche, 2010]. Tidewater calving glaciers (TWGs)—mountain glaciers whose termini reach the sea and are generally grounded on the seafloor—also fall into the category of non-representative glaciers because the regional-scale asynchronous behavior of these glaciers clouds their complex relationship with climate. TWGs span the globe; they can be found both fringing ice sheets and in high-latitude regions of each hemisphere. TWGs are known to exhibit cyclic behavior, characterized by slow advance and rapid, unstable retreat, largely independent of short-term climate forcing. This so-called TWG cycle, first described by Post [1975], provides a solid foundation upon which modern investigations of TWG stability are built. Scientific understanding has developed rapidly as a result of the initial recognition of their asynchronous cyclicity, rendering greater insight into the hierarchy of processes controlling regional behavior. This has improved the descriptions of the strong dynamic feedbacks present during retreat, the role of the ocean in TWG dynamics, and the similarities and differences between TWG and ice sheet outlet glaciers that can often support floating tongues.
%B Eos, Transactions American Geophysical Union
%V 92
%P 305–306
%G eng
%U http://dx.doi.org/10.1029/2011EO370001
%R 10.1029/2011EO370001
%0 Journal Article
%J Geophysical Research Letters
%D 2011
%T An increase in crevasse extent, West Greenland: Hydrologic implications
%A Colgan, William
%A Steffen, Konrad
%A McLamb, W. Scott
%A Waleed Abdalati
%A Rajaram, Harihar
%A Roman J. Motyka
%A Phillips, Thomas
%A Robert S Anderson
%K crevasses
%K Greenland
%K mass balance
%K velocity
%X We compare high-resolution 1985 and 2009 imagery to assess changes in crevasse extent in the Sermeq Avannarleq ablation zone, West Greenland. The area occupied by crevasses >2 m wide significantly increased (13 ± 4%) over the 24-year period. This increase consists of an expansion of existing crevasse fields, and is accompanied by widespread changes in crevasse orientation (up to 45°). We suggest that a combination of ice sheet thinning and steepening are responsible for the increase in crevasse extent. We examine the potential impact of this change on the hydrology of the ice sheet. We provide a first-order demonstration that moulin-type drainage is more efficient in transferring meltwater fluctuations to the subglacial system than crevasse-type drainage. As enhanced basal sliding is associated with meltwater “pulses”, an increase in crevasse extent can therefore be expected to result in a net decrease in basal sliding sensitivity. An increase in crevasse extent may also accelerate cryo-hydrologic warming and enhance surface ablation.
%B Geophysical Research Letters
%V 38
%P n/a–n/a
%G eng
%U http://dx.doi.org/10.1029/2011GL048491
%R 10.1029/2011GL048491
%0 Journal Article
%J Tectonophysics
%D 2011
%T Reevaluation of the viscoelastic and elastic responses to the past and present-day ice changes in Southeast Alaska
%A Tatsuru Sato
%A Chris F. Larsen
%A Miura, S.
%A Ohta, Y.
%A Fujimoto, H.
%A Sun, W.
%A Roman J. Motyka
%A Jeffrey T. Freymueller
%B Tectonophysics
%V 511
%P 79–88
%G eng
%R 10.1016/j.tecto.2010.05.009
%0 Journal Article
%J Journal of Geophysical Research
%D 2011
%T Submarine melting of the 1985 Jakobshavn Isbræ floating tongue and the triggering of the current retreat
%A Roman J. Motyka
%A Martin Truffer
%A Mark Fahnestock
%A Mortensen, J.
%A Rysgaard, S.
%A I M Howat
%B Journal of Geophysical Research
%V 116
%P F01007
%G eng
%R 10.1029/2009JF001632
%0 Journal Article
%J Journal of Geophysical Research
%D 2010
%T Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland
%A Jason M Amundson
%A Mark Fahnestock
%A Martin Truffer
%A Brown, J.
%A M P Lüthi
%A Roman J. Motyka
%B Journal of Geophysical Research
%V 115
%P F01005
%G eng
%R 10.1029/2009JF001405
%0 Journal Article
%J Journal of Geophysical Research
%D 2010
%T Tectonic block motion and glacial isostatic adjustment in southeast Alaska and adjacent Canada constrained by GPS measurements
%A Elliott, J.L.
%A Chris F. Larsen
%A Jeffrey T. Freymueller
%A Roman J. Motyka
%B Journal of Geophysical Research
%V 115
%P B09407
%G eng
%R 10.1029/2009JB007139
%0 Journal Article
%J Journal of Glaciology
%D 2010
%T Volume change of Jakobshavn Isbrae, West Greenland:: 198519972007
%A Roman J. Motyka
%A Mark Fahnestock
%A Martin Truffer
%B Journal of Glaciology
%V 56
%P 635–646
%G eng
%U http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=56&issue=198&spage=635
%0 Journal Article
%J Journal of Glaciology
%D 2009
%T Terminus dynamics at an advancing glacier: Taku Glacier, Alaska
%A Martin Truffer
%A Roman J. Motyka
%A Hekkers, M.
%A I M Howat
%A King, M.A.
%B Journal of Glaciology
%V 55
%P 1052–1060
%G eng
%U http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=55&issue=194&spage=1052
%0 Journal Article
%J Journal of Glaciology
%D 2008
%T Correspondence: Another surge of Variegated Glacier, Alaska, USA, 2003/04
%A Harrison, W.
%A Roman J. Motyka
%A Martin Truffer
%B Journal of Glaciology
%V 54
%P 192-200
%G eng
%U http://www.ingentaconnect.com/content/igsoc/jog/2008/00000054/00000184/art00019
%R doi:10.3189/002214308784409134
%0 Journal Article
%J Geophysical Research Letters
%D 2008
%T Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
%A Jason M Amundson
%A Martin Truffer
%A M P Lüthi
%A Mark Fahnestock
%A West, M.
%A Roman J. Motyka
%B Geophysical Research Letters
%V 35
%P L22501
%G eng
%U http://www.agu.org/pubs/crossref/2008/2008GL035281.shtml
%0 Journal Article
%J Journal of Glaciology
%D 2008
%T Seasonal fluctuations in the advance of a tidewater glacier and potential causes: Hubbard Glacier, Alaska, USA
%A Ritchie, J.B.
%A C S Lingle
%A Roman J. Motyka
%A Martin Truffer
%B Journal of Glaciology
%V 54
%P 401–411
%G eng
%U http://openurl.ingenta.com/content/xref?genre=article&issn=0022-1430&volume=54&issue=186&spage=401
%0 Journal Article
%J Journal of Glaciology
%D 2007
%T Flotation and retreat of a lake-calving terminus, Mendenhall Glacier, southeast Alaska, USA
%A Boyce, E.S.
%A Roman J. Motyka
%A Martin Truffer
%B Journal of Glaciology
%V 53
%P 211–224
%G eng
%0 Journal Article
%J J. Geophys. Res
%D 2007
%T Glacier changes in southeast Alaska and northwest British Columbia and contribution to sea level rise
%A Chris F. Larsen
%A Roman J. Motyka
%A Anthony A. Arendt
%A Echelmeyer, K.A.
%A Geissler, P.E.
%B J. Geophys. Res
%V 112
%P F01007
%G eng
%0 Journal Article
%J Annals of Glaciology
%D 2007
%T Glaciervolcano interactions in the North Crater of Mt Wrangell, Alaska
%A Benson, C.S.
%A Roman J. Motyka
%A McNUTT, S.
%A M P Lüthi
%A Martin Truffer
%B Annals of Glaciology
%V 45
%P 48–57
%G eng
%0 Journal Article
%J Journal of geophysical research
%D 2007
%T Hubbard Glacier, Alaska: 2002 closure and outburst of Russell Fjord and postflood conditions at Gilbert Point
%A Roman J. Motyka
%A Martin Truffer
%B Journal of geophysical research
%V 112
%P F02004
%G eng
%0 Journal Article
%J Alaska Park Science
%D 2007
%T Post Little Ice Age Glacial Rebound in Glacier Bay National Park and Surrounding Areas
%A Roman J. Motyka
%A Chris F. Larsen
%A Jeffrey T. Freymueller
%A Echelmeyer, K.A.
%B Alaska Park Science
%V 6
%P 36–41
%G eng
%0 Journal Article
%J Landslides
%D 0
%T Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska
%A Wieczorek, Gerald
%A Geist, Eric
%A Roman J. Motyka
%A Jakob, Matthias
%X An unstable rock slump, estimated at 5 to 10 × 106 m3, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3–4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green’s law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours.
%B Landslides
%V 4
%P 205-215
%G eng
%U http://www.ingentaconnect.com/content/klu/10346/2007/00000004/00000003/00000084
%R doi:10.1007/s10346-007-0084-1
%0 Journal Article
%J Journal of Glaciology
%D 0
%T Hubbard Glacier update: another closure of Russell Fiord in the making?
%A Roman J. Motyka
%A Lawson, Daniel
%A Finnegan, David
%A Kalli, George
%A Molnia, Bruce
%A Anthony A. Arendt
%B Journal of Glaciology
%V 54
%P 562-564
%G eng
%U http://www.ingentaconnect.com/content/igsoc/jog/2008/00000054/00000186/art00020
%R doi:10.3189/002214308785837066