AUTHOR=Durkin William J. , Bartholomaus Timothy C. , Willis Michael J. , Pritchard Matthew E. 

TITLE=Dynamic Changes at Yahtse Glacier, the Most Rapidly Advancing Tidewater Glacier in Alaska

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 5 - 2017

YEAR=2017

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2017.00021

DOI=10.3389/feart.2017.00021

ISSN=2296-6463

ABSTRACT=Since 1990, Yahtse Glacier in southern Alaska has advanced at an average rate of ∼100 m/yr
despite of a negative mass balance, widespread thinning in its accumulation area, and a low
accumulation-area ratio. To better understand the interannual and seasonal changes at Yahtse
and the processes driving these changes, we construct velocity and ice surface elevation time
series spanning the years 1985-2014 and 2000-2014, respectively, using satellite optical and
synthetic aperture radar (SAR) observations. In terms of seasonal changes, we find contrasting
dynamics above and below a steep (up to 18% slope) icefall located approximately 6 km from the
terminus. Above the icefall, speeds peak in May and reach minima in October synchronous with
the development of a calving embayment at the terminus. This may be caused by an efficient,
channelized subglacial drainage system that focuses subglacial discharge into a plume, resulting
in a local increase in calving and submarine melting. However, velocities near the terminus are
fastest in the winter, following terminus retreat, possibly off of a terminal moraine resulting in
decreased backstress. Between 1996-2014 the terminus decelerated by ∼40% at an average
rate of ∼0.4 m/day/yr , transitioned from tensile to compressive longitudinal strain rates,
and dynamically thickened at rates of 1-6 m/yr , which we hypothesize is in response to the
development and advance of a terminal moraine. The described interannual changes decay
significantly upstream of the icefall, indicating that the icefall may inhibit the upstream transmission
of stress perturbations. We suggest that diminished stress transmission across the icefall could
allow Yahtse’s upper basin to remain in a state of mass drawdown despite of moraine-enabled
terminus advance. Our work highlights the importance of glacier geometry in controlling tidewater
glacier re-advance, particularly in a climate favoring increasing equilibrium line altitudes.