Lamplugh Glacier is situated on the western shore of Glacier Bay at the entrance to Johns Hopkins Inlet in Glacier Bay National Park and Preserve, about 109 miles (175 km) southeast of Yakutat and 55 miles (89 km) northwest of Gustavus, Alaska. The Lamplugh Glacier flows out of the Brady Icefield from an elevation of about 2,460 feet (750 m) and trends north for 13 miles (21 km) where, at an elevation of about 2,200 feet (671 m), the ice flow splits into the Lamplugh and Reid Glaciers. The Lamplugh Glacier continues north-northwest for 8 miles (13 km) to tidewater and the Reid Glacier flows north for 5 miles (8 km) to Reid Inlet but is no longer tidal. Lamplugh Glacier was named by Lawrence Martin of the U.S. Geological Survey around 1912 for the English geologist George William Lamplugh, who visited Glacier Bay in 1884. The Lamplugh Glacier is about 0.75 miles (1.2 km) wide at the terminus. The ice terminus rises to a height of 150–160 feet (46–49 m). The flow rate of the glacier is estimated at 900–1,000 feet (270–300 m) per year. The terminus is currently receding by calving in the central part of the ice face. The western third and maybe also the eastern third of the terminus are grounded, and only at the highest tides does saltwater reach the entire glacial toe. A large subglacial stream flows from the central part of the terminus, but its position shifts laterally from year to year, sometimes in response to the build-up of fluvial sediment as a small delta that can be seen at low tide. This turbid subglacial stream discharges large volumes of sediment-laden water into the fjord where the outwash has built up extensive mudflats along the entire face of the glacier.

Recent studies have documented that the majority of alpine glaciers worldwide have been losing ice mass during the past century and have been contributing to global sea level rise. A small fraction of the world’s ice mass is represented by temperate alpine glaciers, but because these are losing ice mass more quickly than polar ice, they are contributing disproportionately and significantly to sea level rise. Averaged over the past 20 years, the loss of ice from Alaskan glaciers represents the largest regional contribution to global sea level rise outside of the polar ice sheets. For example, alpine glaciers in Alaska and Canada are thinning so rapidly that they made a larger contribution to global sea level rise than the Greenland ice sheet during the latter half of the 20th century. Glaciers cover ∼3.5% of the surface area in Alaska, but within the Gulf of Alaska watershed, this coverage exceeds 15%. Most glaciers along the Gulf of Alaska have been retreating since achieving their Little Ice Age maximums sometime between 1750 and 1900 AD, in some cases quite rapidly. Nowhere in Alaska have these effects been more dramatic than along the coastal mountains of Southeast Alaska where high annual snow accumulation rates (up to 13 feet/year (4 m/yr) water equivalent) and severe annual ice ablation (up to -46 feet/year (-14 m/yr) water equivalent) result in extremely high rates of ice mass exchange. The surface geometry of these glaciers, called glacial hypsometry, is the distribution of glacier area over elevation and is important for long-term glacier response to climatic changes. Glacier hypsometry is determined by valley shape, topographic relief, and ice volume distribution. The Equilibrium Line Altitude is the elevation that separates the accumulation and ablation zones on a glacier, and its elevation fluctuations relative to the glacier hypsometry determine the glacier sensitivity to climate change. For example, Lamplugh Glacier originates from a flow divide at an elevation of approximately 2,460 feet (750 m) and has a large area near the long-term Equilibrium Line Altitude, and therefore, is more sensitive to climatic fluctuations than one with little area near the Equilibrium Line Altitude. Measurements show that on average the glacier-wide mass balance on the Lamplugh Glacier between 1995 and 2011 was -1.0 feet/year (-0.32 m/yr), while a maximum average thickness loss rate of 1.8 feet/year (0.54 m/yr) occurred between 2000 and 2005.

In June 2016, a massive landslide spread rocky debris more than 6 miles (10 km) across the upper Lamplugh Glacier. The Lamont-Doherty Earth Observatory estimated the slide involved more than 132 million tons of rock. The slide caused seismic tremors of magnitude 5.5 according to the Alaska Earthquake Center. Deglaciation of the Glacier Bay Icefield, which reached a maximum thickness of 0.9 miles (1.5 km) during the Little Ice Age formed Glacier Bay proper. Post-glacial rebound as a result of deglaciation contributes to uplift rates of up to 1.2 inches/year (30 mm/yr). Adding to this instability, the Fairweather Fault runs approximately north-south through the western peninsula under the Brady Icefield and accommodates slip along the transform boundary between the Pacific and North American Plates. The Lamplugh rock avalanche originated from a bedrock ridge at an elevation of approximately 1.3 miles (2.1 km) and traveled a distance of about 6.5 miles (10.5 km), including about 4 miles (6.4 km) across the surface of the Lamplugh Glacier. The source area consists of sedimentary and metamorphic rocks from the Triassic to Cretaceous Kelp Bay Group, including phyllite, quartzite, greenschist, greenstone, and greywacke. The north-facing ridge from which the rock avalanche originated drops at an average slope of 48° to an elevation of approximately 2,953 feet (900 m) before sloping toward the surface of the Lamplugh Glacier at an average gradient of 8°. The average gradient of the Lamplugh Glacier along the portion of the valley floor over which the rock avalanche traveled is approximately 1.3°. The Lamplugh Glacier flows through a mountain valley that is approximately 8,202 feet (2,500 m) wide and confined by steep mountains on both sides. The rock avalanche was confined by mountains on the west but did not travel far enough across the valley to reach the mountains on the east side. The frontal margin of the Lamplugh rock avalanche lies approximately 8,600 m from the terminus of the Lamplugh Glacier and will start flowing into Glacier Bay in about 2030. Read more here and here. Explore more of Lamplugh Glacier here: