Monitoring the Dynamics of the Bering Glacier with Global Fiducials Imagery

Abstract:

The 1,000 km² Bering Glacier Global Fiducials site includes the glacier’s piedmont lobe and parts of the adjacent coastal foreland to the south and the Chugach Mountains to the north. The site was created to monitor the post-surge dynamics of Bering Glacier following a 1993-1995 surge that resulted in a terminus advance of ~6 km. Global Fiducials imagery has not only documented the onset of a second surge that began in 2008 and continued through 2012; but also the accelerating retreat of the glacier’s terminus, characterized by the calving of large tabular icebergs; a massive ice-rock avalanche that occurred in September 2005; and in 2014, a major change in the hydrology of Berg Lake, the ice-marginal lake dammed by the terminus of Bering’s Steller Lobe, which comprises the northwestern part of the glacier’s piedmont lobe.

Following the 1993-1995 surge, Bering’s terminus retreated rapidly. Between September 1996 and mid-2010, it retreated a maximum of 7 km. During the second surge, part of the terminus advanced >3.5 km with maximum advance rates >19 m/d in 2011. Since then, the glacier has thinned rapidly and resumed retreating, with part of the terminus retreating >6 km.

October 2005 Fiducials imagery was used to evaluate one of the largest-ever non-earthquake-generated Alaskan landslides. It originated from just below the south-facing summit of 3,236 m Mount Steller, removing a near-summit hanging glacier and a substantial amount of bedrock, ice, and snow. Much of the displaced slide-mass landed on a Bering Glacier tributary, ~2,500 m below. The slide, with a volume of ~50x10⁶ m³, extended >8 km from the point of impact. Fiducials imagery confirmed that near-summit meltwater had played a role in destabilizing sub-glacial permafrost resulting in the mass wasting event. Subsequent melting continued for more than a year.

Fiducials imagery also documented that through the early 21^st century, Berg Lake drained through a bedrock outlet into the Bering River gorge. Subsequent terminus thinning lowered the lake surface below this outlet. Seven times since September 2014, Berg Lake has rapidly drained sub-glacially, flooding an ~100 km² area of the coastal foreland.

Global Fiducials imagery has proven beneficial in monitoring the dynamics of Bering Glacier.