suiattle river glacier retreat – From a Glaciers Perspective

Vista Glacier in 1998 and 2016 Digital Globe images with the the 1984 terminus red arrow and 2015 terminus yellow arrow, Point A is the rock seen below the glacier in 1994 image below and Point B is where the advance moraine reached the valley bottom.

Vista Glacier is a valley glacier flowing down the northeast side of Glacier Peak (Dakobed) that drains into the Suiattle River. The glacier begins at 2475 m beneath Kennedy Peak. We examined all of the glaciers around Glacier Peak in detail from 1993-1997 to document their changes since first closely observed by C.E. Rusk 100 years earlier. The glacier during the LIA joined the Ermine Glacier and extended down to 1345 m. By 1900 when Asahel Curtis photographed this glacier it had retreated 1300 m. By 1946 the glacier had retreated 1900 m from its LIA moraine, separated from Ermine Glacier and terminated at ~1900 m. In 1955 the glacier began a slow advance, all major Glacier Peak glaciers advanced during this period, that had ended by 1975 with a total advance of 105 m (Pelto and Hedlund, 2001).

Vista Glacier in 1988 aerial image illustrating the glacier is still adjacent to advance moraine.

In 1985 at our first visit the glacier was again retreating, total retreat was 10-20 meters from the advance moraine. By 1994 the glacier had retreated 90-100 m with the lower part of the glacier thin and crevassed. By 1997 the glacier had retreated beyond the 1946 position. The retreat accelerated after 2003 and had retreated and by 2016 the retreat from the 1984 mapped position was 410 m, a rate of ~13 m/year. The terminus is now at 1900 m.

In 1994 Cliff Hedlund and I were surveying the terminus when we found a beautiful ice cave beneath the glacier, see below. The rock just behind Cliff in the cave is apparent now out in the open in the Digital Globe image from 2016 and the LIDAR image from 2015 (Point A). Cliff was ahead of his time with the homemade neon colored gear that is perfect in an ice cave.

The red arrow in the image below looking down glacier in 1997 indicates the ice surface level in 1985, the glacier has thinned 20 meters in this region. Measuring snow depth up the middle of this glacier in 1994 and 1997 we found limited areas with accumulation of greater than 2 m in early August. This glacier is prone to losing most of its snow cover in many years such as occurred 2005, 2009, 2015 and 2019. Overall. This indicates considerable retreat will occur even with present climate. From 2013-2020 the end of summer snowline avearaged 2350 m, leaving just 35% of the glacier in the accumulatioin zone each year. To have an equilibrium balance North Cascade glaciers need an AAR of at least 55%, the percentage of glacier in accumulation zone (Pelto and Brown, 2012). We will back in the field this coming summer for the 38th consecutive year measuring the response of North Cascade glaciers to climate change.

1984 USGS Map of Vista Glacier and 2015 LIDAR (WA DNR) of Vista Glacier. Red line is the 1984 terminus and yellow line the 2015 terminus location. Note lack of crevasses in lower half of glacier.

Terminus change map of Vista Glacier from 1984-2015.

Cliff Hedlund in subglacial tunnel leading to Rock A in 1994.

View across lower half of glacier in 1997 towards Ermine Glacier indicating limited crevassing and flow of this thin section of the glacier

Vista Glacier in 2006 with the blue dots indicating the margin and resulting moraines emplaced by the advance from the 1950’s into the 1970’s.

Honeycomb Glacier in Google Earth imagery from 1998 and 2016. The dark orange line is the 1998 margin, we mapped the margin in the field in 1995 and in 2002. The light orange line is the 2007 margin and the yellow line the 2016 margin. Note crevassing diminished as well.

Honeycomb Glacier is one of the longest and largest glaciers in the North Cascades. In 1979 it was 3.9 km long and had an area of 3.5 km2. By 2016 the area had declined to 2,6 km2 and it has retreated 2.6 kilometers since its Little Ice Age Maximum. The glacier was an imposing site to C.E. Rusk who recounted his early 20th century exploration (1924). Like all 47 glaciers observed by the North Cascade Glacier Climate Project it has retreated significantly since 1979. The glacier feeds the headwaters of the Suiattle River, which is also an important salmon stream, for chinook, coho, sockeye and pink salmon (WDFW,2018).

A 1960 photograph taken by Austin Post, USGS shows the glacier ending with no lake at its terminus. The terminus is gentle and has no crevasses, indicating it is relatively stagnant and poised to melt away. The glacier has retreated 1.3 km from its Little Ice Age moraines at this point. In 1967 another Austin Post image indicates a new small lake forming at the terminus.

In 1995 we mapped the margin of the glacier ending in this lake, where the glacier ended in 1967 and took a photograph back to the glacier. As seen below retreat to this point was 400 m.

A pair of images from Bill Arundell in 1973 and Lowell Skoog in 2006 indicate the scale of the retreat, these images do not show the actual terminus but do show the main nunatak-rock island and how much it has become exposed in the 33 years. This nunatak was hardly evident in 1960, and in a 1940 image of the glacier literally did not yet exist.

The terminus had retreated 400 m from the 1967 position to 1995. In 1987 a new lake began to form at the terminus of the glacier at 1680 m. The glacier is shown ending in this lake in 2002 from both the far end of the lake and the nunatak above the lake, the glacier had retreated 210 m since 1995. In 2006 the glacier retreated from the end of this lake. This is a shallow lake that may eventually be filled in by glacier sediments. The terminus is flat and stagnant ending at 1680 m in the lake. Thus, the rapid retreat will continue, the glacier is still not close to acheiving a post LIA equilibrium. Glacier retreat from 1940-1967 averaged 9 m/year. Retreat was minor between 1967 and 1979. The retreat rate from 1979-1998 was greater at 16 m/year, with a total retreat of 300 m. The retreat than increased from 1998-2016 with the west branch retreating 800 m and the east branch 500 m. The nunatak in the middle of the glacier, which was beneath the ice in 1940 was 90 m above the ice in 2002 when we mapped it. By 2009 it was no longer a nunatak as the glacier did not merge downstream of the this bedrock knob.

The retreat of this section of the glacier results in a reduced melt area of ~1 km2 in the last 40 years. This in turn reduces summer glacier runoff as there is no longer snow/ice melting each day under the warm summer conditions. Flow in the Suiattle River in late summer and early fall has declined as a result. In 2002 during mapping of the glacier images from above and below the nunatak indicate the stagnant nature of the ice below the nunatak.