Austin Post

How much do we really know about glacier surging

Abstract Some of the ideas about glacier surging are considered, mainly but not entirely in the light of observations of temperate glaciers in Alaska, U.S.A., made within the last 15 years. Climate has an influence on surge recurrence interval. Climate and weather also affect surge initiation, termination and magnitude. Regional studies lead to the speculation that subglacial “till” plays a key role in surging, and it has been found under all surge-type glaciers studied so far, including Black Rapids and Variegated Glaciers, Alaska. In most of the glaciers studied, till deformation processes dominate the motion in quiescence. The linked-cavity model of surge triggering and rapid motion is not consistent with these observations, but the limited coverage of the observations does not rule it out under parts of the glaciers studied. The till observations in Alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers. The role of stored water, which observations show to be active even in winter on Black Rapids Glacier, is noted.

TAKU AND LE CONTE GLACIERS, ALASKA: CALVING-SPEED CONTROL OF LATE-HOLOCENE ASYNCHRONOUS ADVANCES AND RETREATS

Taku Glacier, Alaska, which until around 1950 calved icebergs into tidewater, has advanced 7.3 km since 1890, although all other valley glaciers in the immediate area have retreated. This anomalous...

HOLOCENE HISTORY OF BERING GLACIER, ALASKA: A PRELUDE TO THE 1993–1994 SURGE

Within the last few centuries, Bering Glacier, the largest and longest glacier in continental North America, began to retreat from its Neoglacial maximum position. This position also represents the Holocene maximum extent of the glacier. For much of the period between 8000 yr B.P. and about 1500 yr B.P., the Bering Glacier was in a retracted position, although a readvance may have occurred about 5000 yr B.P. A major readvance began about 1500 yr B.P., culminating with the glacier reaching its Holocene maximum extent between 1000 and 500 years ago. During the last millennium, the glacier margin fluctuated near this maximum position, only beginning to retreat within the last 100–200 years. This century, the recession from the Neoglacial maximum position has been interrupted by at least six surges that have displaced parts of the glaciers terminus forward. Prior to the latest surge, beginning in 1993, retreat resulted in the net loss of more than 130 km2 of glacier in the terminus region, as much as 12 km o...

Airborne and spaceborne DEM- and laser altimetry-derived surface elevation and volume changes of the Bering Glacier system, Alaska, USA, and Yukon, Canada, 1972-2006

Using airborne and spaceborne high-resolution digital elevation models and laser altimetry, we present estimates of interannual and multi-decadal surface elevation changes on the Bering Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006. We find: (1) the rate of lowering during 1972-95 was 0.9 � 0.1 m a -1 ; (2) this rate accelerated to 3.0 � 0.7 m a -1 during 1995-2000; and (3) during 2000-03 the lowering rate was 1.5 � 0.4 m a -1 . From 1972 to 2003, 70% of the area of the system experienced a volume loss of 191 � 17 km 3 , which was an area-average surface elevation lowering of 1.7 � 0.2 m a -1 . From November 2004 to November 2006, surface elevations across Bering Glacier, from McIntosh Peak on the south to Waxell Ridge on the north, rose as much as 53 m. Up-glacier on Bagley Ice Valley about 10 km east of Juniper Island nunatak, surface elevations lowered as much as 28 m from October 2003 to October 2006. NASA Terra/MODIS observations from May to September 2006 indicated muddy outburst floods from the Bering terminus into Vitus Lake. This suggests basal-englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006.

Surging, accelerating surface lowering and volume reduction of the Malaspina Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006

Near-concurrent surges and multi-decadal surface-elevation changes on the Malaspina Glacier system Alaska, USA, and Yukon, Canada, were investigated using digital elevation models and laser altimetry from airborne and space-borne sensors. Surface-elevation changes on Seward Lobe in two time periods support a hypothesis of moraine folding by a mechanism of sequential surges alternating from southeast to south-southwest. The near-concurrent surges of Agassiz, Lower Seward and Marvine glaciers support a hypothesis of englacial water storage being a critical factor of surging. Acceleration of area-average surface lowering on the piedmont glaciers occurred, from 1.5 � 0.1 m a -1 between 1972 and 1999 to 2.3 � 0.3 m a -1 between 1999 and 2002. On the western half of Upper Seward Glacier, above 1600 m, acceleration of surface lowering occurred from 2000 to 2003 relative to that from 1976 to 2000, indicating an effect from the surge of Lower Seward Glacier. From 2003 to 2006, the rate of surface lowering on Upper Seward Glacier has moderated back to the pre-2000 rate, indicating a recovery of surface elevation following the surge. From 1972 to 2002, the Malaspina Glacier system lost 156 � 19 km 3 (ice equivalent) on an area of 3661 km 2 .

Alaskan glaciers: Recent observations in respect to the earthquake-advance theory

Preliminary aerial photographic studies indicate that the Alaskan earthquake produced some rockfalls but no significant snow and ice avalanches on glaciers. No rapid, short-lived glacier advances (surges) are conclusively associated with this earthquake. Recent evidence fails to support the earthquake-advance theory of Tarr and Martin.

The Neoglacial landscape and human history of Glacier Bay, Glacier Bay National Park and Preserve, southeast Alaska, USA:

The Neoglacial landscape of the Huna Tlingit homeland in Glacier Bay is recreated through new interpretations of the lower Bays fjordal geomorphology, late Quaternary geology and its ethnographic landscape. Geological interpretation is enhanced by 38 radiocarbon dates compiled from published and unpublished sources, as well as 15 newly dated samples. Neoglacial changes in ice positions, outwash and lake extents are reconstructed for c. 5500—200 cal. yr ago, and portrayed as a set of three landscapes at 1600—1000, 500—300 and 300—200 cal. yr ago. This history reveals episodic ice advance towards the Bay mouth, transforming it from a fjordal seascape into a terrestrial environment dominated by glacier outwash sediments and ice-marginal lake features. This extensive outwash plain was building in lower Glacier Bay by at least 1600 cal. yr ago, and had filled the lower bay by 500 cal. yr ago. The geologic landscape evokes the human-described landscape found in the ethnographic literature. Neoglacial climate and landscape dynamism created difficult but endurable environmental conditions for the Huna Tlingit people living there. Choosing to cope with environmental hardship was perhaps preferable to the more severely deteriorating conditions outside of the Bay as well as conflicts with competing groups. The central portion of the outwash plain persisted until it was overridden by ice moving into Icy Strait between AD 1724—1794. This final ice advance was very abrupt after a prolonged still-stand, evicting the Huna Tlingit from their Glacier Bay homeland.