%0 Journal Article %J Journal of Glaciology %D 2018 %T Active seismic studies in valley glacier settings: strategies and limitations %A ZECHMANN, JENNA M. %A BOOTH, ADAM D. %A Truffer, Martin %A Gusmeroli, Alessio %A Amundson, Jason M. %A Larsen, Christopher F. %K glacial tills %K glacier geophysics %K glaciological instruments and methods %K seismics %K subglacial %X Subglacial tills play an important role in glacier dynamics but are difficult to characterize in situ. Amplitude Variation with Angle (AVA) analysis of seismic reflection data can distinguish between stiff tills and deformable tills. However, AVA analysis in mountain glacier environments can be problematic: reflections can be obscured by Rayleigh wave energy scattered from crevasses, and complex basal topography can impede the location of reflection points in 2-D acquisitions. We use a forward model to produce challenging synthetic seismic records in order to test the efficacy of AVA in crevassed and geometrically complex environments. We find that we can distinguish subglacial till types in moderately crevassed environments, where ‘moderate' depends on crevasse spacing and orientation. The forward model serves as a planning tool, as it can predict AVA success or failure based on characteristics of the study glacier. Applying lessons from the forward model, we perform AVA on a seismic dataset collected from Taku Glacier in Southeast Alaska in March 2016. Taku Glacier is a valley glacier thought to overlay thick sediment deposits. A near-offset polarity reversal confirms that the tills are deformable. %B Journal of Glaciology %V 64 %P 796–810 %8 oct %G eng %U https://www.cambridge.org/core/product/identifier/S0022143018000692/type/journal{\_}article %R 10.1017/jog.2018.69 %0 Journal Article %J The Cryosphere %D 2018 %T Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison %A Goelzer, Heiko %A Nowicki, Sophie %A Edwards, Tamsin %A Beckley, Matthew %A Abe-Ouchi, Ayako %A Aschwanden, Andy %A Calov, Reinhard %A Gagliardini, Olivier %A Gillet-Chaulet, Fabien %A Golledge, Nicholas R. %A Gregory, Jonathan %A Greve, Ralf %A Humbert, Angelika %A Huybrechts, Philippe %A Kennedy, Joseph H. %A Larour, Eric %A Lipscomb, William H. %A Le clec'h, Sébastien %A Lee, Victoria %A Morlighem, Mathieu %A Pattyn, Frank %A Payne, Antony J. %A Rodehacke, Christian %A Rückamp, Martin %A Saito, Fuyuki %A Schlegel, Nicole %A Seroussi, Helene %A Shepherd, Andrew %A Sun, Sainan %A van de Wal, Roderik %A Ziemen, Florian A. %X Abstract. Earlier large-scale Greenland ice sheet sea-level projections (e.g. those run during the ice2sea and SeaRISE initiatives) have shown that ice sheet initial conditions have a large effect on the projections and give rise to important uncertainties. The goal of this initMIP-Greenland intercomparison exercise is to compare, evaluate, and improve the initialisation techniques used in the ice sheet modelling community and to estimate the associated uncertainties in modelled mass changes. initMIP-Greenland is the first in a series of ice sheet model intercomparison activities within ISMIP6 (the Ice Sheet Model Intercomparison Project for CMIP6), which is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the ice sheets. Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of (1) the initial present-day state of the ice sheet and (2) the response in two idealised forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without additional forcing) and in response to a large perturbation (prescribed surface mass balance anomaly); they should not be interpreted as sea-level projections. We present and discuss results that highlight the diversity of data sets, boundary conditions, and initialisation techniques used in the community to generate initial states of the Greenland ice sheet. We find good agreement across the ensemble for the dynamic response to surface mass balance changes in areas where the simulated ice sheets overlap but differences arising from the initial size of the ice sheet. The model drift in the control experiment is reduced for models that participated in earlier intercomparison exercises. %B The Cryosphere %V 12 %P 1433–1460 %8 apr %G eng %U https://www.the-cryosphere.net/12/1433/2018/ %R 10.5194/tc-12-1433-2018 %0 Journal Article %J Journal of Glaciology %D 2016 %T Modeling the evolution of the Juneau Icefield between 1971 and 2100 using the Parallel Ice Sheet Model (PISM) %A Ziemen, Florian A %A Hock, Regine %A Aschwanden, Andy %A Khroulev, Constantine %A Kienholz, Christian %A MELKONIAN, ANDREW %A ZHANG, JING %B Journal of Glaciology %V 62 %P 199–214 %G eng %0 Journal Article %J Geophys. Res. Lett. %D 2015 %T Dynamic jamming of iceberg-choked fjords %A Peters, I %A Amundson, J. M. %A Cassotto, R %A Fahnestock, M %A Darnell, K %A Truffer, M. %A Zhang, W. %K 10.1002/2014GL062715 and glaciers %K calving %K icebergs %K jamming %B Geophys. Res. Lett. %V 42 %P 1122–1129 %G eng %R 10.1002/2014GL062715 %0 Journal Article %J Journal of Glaciology %D 2015 %T Run-away thinning of the low elevation Yakutat Glacier and its sensitivity to climate change %A Truessel, Barbara %A Martin Truffer %A Regine Hock %A Roman Motyka %A Matthias Huss %A Jing Zhang %B Journal of Glaciology %V 61 %G eng %R 10.3189/2015JoG14J125 %0 Journal Article %J Science %D 2014 %T Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica %A Rebesco, M %A Domack, E %A Zgur, F %A Lavoie, C %A Leventer, A %A Brachfeld, S %A Willmott, V %A Halverson, G %A Truffer, M %A Scambos, T %A Pettit, Erin C %B Science %I American Association for the Advancement of Science %V 345 %P 1354–1358 %G eng %0 Journal Article %J Climate of the Past %D 2014 %T Coupled ice sheet–climate modeling under glacial and pre-industrial boundary conditions %A Ziemen, F. A. %A Rodehacke, C. B. %A Mikolajewicz, U. %X In the standard Paleoclimate Modelling Intercomparison Project (PMIP) experiments, the Last Glacial Maximum (LGM) is modeled in quasi-equilibrium with atmosphere–ocean–vegetation general circulation models (AOVGCMs) with prescribed ice sheets. This can lead to inconsistencies between the modeled climate and ice sheets. One way to avoid this problem would be to model the ice sheets explicitly. Here, we present the first results from coupled ice sheet–climate simulations for the pre-industrial times and the LGM. Our setup consists of the AOVGCM ECHAM5/MPIOM/LPJ bidirectionally coupled with the Parallel Ice Sheet Model (PISM) covering the Northern Hemisphere. The results of the pre-industrial and LGM simulations agree reasonably well with reconstructions and observations. This shows that the model system adequately represents large, non-linear climate perturbations. A large part of the drainage of the ice sheets occurs in ice streams. Most modeled ice stream systems show recurring surges as internal oscillations. The Hudson Strait Ice Stream surges with an ice volume equivalent to about 5 m sea level and a recurrence interval of about 7000 yr. This is in agreement with basic expectations for Heinrich events. Under LGM boundary conditions, different ice sheet configurations imply different locations of deep water formation. %B Climate of the Past %V 10 %P 1817-1836 %G eng %U http://www.clim-past.net/10/1817/2014/cp-10-1817-2014.html %& 1817 %R 10.5194/cp-10-1817-2014 %0 Journal Article %J The Cryosphere %D 2014 %T The effect of climate forcing on numerical simulations of the Cordilleran ice sheet at the Last Glacial Maximum %A Seguinot, J. %A Khroulev, C. %A Rogozhina, I. %A Stroeven, A. P. %A Zhang, Q. %B The Cryosphere %V 8 %P 1087–1103 %G eng %U http://www.the-cryosphere.net/8/1087/2014/ %R 10.5194/tc-8-1087-2014 %0 Journal Article %J Journal of Glaciology %D 2013 %T Mass balance in the Glacier Bay area of Alaska, USA, and British Columbia, Canada, 1995–2011, using airborne laser altimetry %A Johnson, Austin J %A Chris F. Larsen %A Murphy, Nathaniel %A Anthony A. Arendt %A Zirnheld, S Lee %B Journal of Glaciology %V 59 %P 632–648 %G eng %N 216 %R 10.3189/2013JoG12J101 %0 Journal Article %J Geophysical Research Letters %D 2013 %T An open ocean region in Neoproterozoic glaciations would have to be narrow to allow equatorial ice sheets %A Rodehacke, Christian B. %A Voigt, Aiko %A Ziemen, Florian %A Abbot, Dorian S. %K ice sheet modeling %K Neoproterozoic glaciations %K snowball Earth %X A major goal of understanding Neoproterozoic glaciations and determining their effect on the evolution of life and Earth's atmosphere is establishing whether and how much open ocean there was during them. Geological evidence tells us that continental ice sheets had to flow into the ocean near the equator during these glaciations. Here we drive the Parallel Ice Sheet Model with output from four simulations of the ECHAM5/Max Planck Institute Ocean Model atmosphere-ocean general circulation model with successively narrower open ocean regions. We find that extensive equatorial ice sheets form on marine margins if sea ice extends to within about 20° latitude of the equator or less (Jormungand-like and hard snowball states), but do not form if there is more open ocean than this. Given uncertainty in topographical reconstruction and ice sheet ablation parameterizations, we perform extensive sensitivity tests to confirm the robustness of our main conclusions. %B Geophysical Research Letters %V 40 %P 5503–5507 %G eng %U http://dx.doi.org/10.1002/2013GL057582 %R 10.1002/2013GL057582 %0 Journal Article %J The Cryosphere %D 2012 %T Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula %A Zagorodnov, V %A Nagornov, O %A Scambos, TA %A Muto, A %A Mosley-Thompson, E %A Erin C Pettit %A Tyuflin, S %B The Cryosphere %I Copernicus GmbH %V 6 %P 675–686 %G eng %0 Journal Article %J Journal of Geophysical Research: Solid Earth %D 2012 %T A detailed view into the eruption clouds of Santiaguito volcano, Guatemala, using Doppler radar %A Scharff, L. %A Ziemen, F. %A Hort, M. %A Gerst, A. %A Johnson, J. B. %K Doppler radar %K eruption dynamics %K Santiaguito volcano %X Using Doppler radar technology we are able to show that eruptions at Santiaguito volcano, Guatemala, are comprised of multiple explosive degassing pulses occurring at a frequency of 0.2 to 0.3 Hz. The Doppler radar system was installed about 2.7 km away from the active dome on the top of Santa Maria volcano. During four days of continuous measurement 157 eruptive events were recorded. The Doppler radar data reveals a vertical uplift of the dome surface of about 50 cm immediately prior to a first degassing pulse. Particle velocities range from 10 to 15 m/s (in the line of sight of the radar). In 80% of the observed eruptions a second degassing pulse emanates from the dome with significantly higher particle velocities (20–25 m/s again line of sight) and increased echo power, which implies an increase in mass flux. We carry out numerical experiments of ballistic particle transport and calculate corresponding synthetic radar signals. These calculations show that the observations are consistent with a pulsed release of material from the dome of Santiaguito volcano. %B Journal of Geophysical Research: Solid Earth %V 117 %P n/a–n/a %G eng %U http://dx.doi.org/10.1029/2011JB008542 %R 10.1029/2011JB008542 %0 Journal Article %J Journal of Glaciology %D 2011 %T The crossover stress, anisotropy and the ice flow law at Siple Dome, West Antarctica %A Erin C Pettit %A Waddington, Edwin D %A Harrison, William D %A Thorsteinsson, Throstur %A Elsberg, Daniel %A Morack, John %A Zumberge, Mark A %B Journal of Glaciology %I International Glaciological Society %V 57 %P 39–52 %G eng %0 Journal Article %J The Cryosphere %D 2008 %T Benchmark experiments for higher-order and full Stokes ice sheet models (ISMIP-HOM) %A Frank Pattyn %A Perichon, L. %A Andy Aschwanden %A Breuer, B. %A de Smedt, B. %A Gagliardini, O. %A Gudmundsson, G. H. %A Hindmarsh, R. C. A. %A Hubbard, A. L. %A Jesse V Johnson %A Kleiner, T. %A Konovalov, Y. %A Martin, C. %A Payne, A. J. %A David Pollard %A Stephen F. Price %A M Rückamp %A Fuyuki Saito %A Souček, O. %A Sugiyama, S. %A Zwinger, T. %B The Cryosphere %V 2 %P 95–108 %G eng %0 Journal Article %J Journal of Glaciology %D 2004 %T Depth-and time-dependent vertical strain rates at Siple Dome, Antarctica %A Elsberg, Daniel H %A Harrison, William D %A Zumberge, Mark A %A Morack, John L %A Erin C Pettit %A Waddington, Edward D %A Husmann, Eric %B Journal of Glaciology %I International Glaciological Society %V 50 %P 511–521 %G eng %0 Journal Article %J Journal of Glaciology %D 2002 %T Measurement of vertical strain and velocity at Siple Dome, Antarctica, with optical sensors %A Zumberge, Mark A %A Elsberg, Daniel H %A Harrison, William D %A Husmann, Eric %A Morack, John L %A Erin C Pettit %A Waddington, Edwin D %B Journal of Glaciology %I International Glaciological Society %V 48 %P 217–225 %G eng