cariboo mountain glacier retreat – From a Glaciers Perspective

Kiwa Glacier retreat from 1986 to 2015 in Landsat images. Red arrow is 1986 terminus and yellow arrow 2015 terminus location. Purple arrow indicates upglacier thinning where more bedrock is exposed. Purple dots indicate the transient snowline

Kiwa Glacier is the longest glacier, at 9 km, in the Cariboo Mountains of British Columbia. The glacier drains northwest from Mount Sir Wilfred Laurier and is near the headwaters of the Fraser River, where it terminates in an expanding lake at 1465 m. Here we examine glacier change from 1986 to 2015. In 1986 the glacier terminated in the 700-800 m long proglacial lake. The glacier has two significant icefalls above the terminus at 2300 m and 1800 m. The lower icefall generating a series of ogives that are generated annually due to seasonal velocity fluctuations. The ogives indicate the glacier velocity below this icefall. There are 20 ogives in the span of approximately 1 km indicating a velocity of 50 m/year. In 2015 the glacier still terminates in the proglacial lake that is now 1400-1500 m long indicating a retreat of 700 m in the thirty years from 1986-2015. The lower 300 m of the glacier is nearly flat suggesting the lake will extend at least that far, note 2010 image from Reiner Thoni, Canadian Mountaineer. This is also the extent that will be lost relatively quickly via iceberg calving and continued surface melt. Above this point flow remains vigorous and retreat could diminish. Upglacier thinning has expanded bedrock areas even separating sections of the glacier, purple arrows. The transient snowline in mid-August in the Landsat images is at 2550 m. Driving through the area last week, the snowline is at 1000 m, quite high for mid-March.

Beedle et al (2015) note that glaciers in the Cariboo Mountains were close to equilibrium from 1952 to 1985 : 9 glaciers advanced, 12 receded, and 11 did not change. After 1985 they noted that all glacier retreated in the Cariboo Mountains. The response time of the glaciers to climate change is the main cause for the differing response of individual glaciers in the region as has been noted in other Pacific Northwest regions (Pelto and Hedlund, 2001 & Tennant et al, 2012). Response times are faster for glaciers with steeper slopes, higher velocity/length ratios and a higher ratio of accumulation-ablation/ ice thickness. The decline of glaciers, warm weather and reduced snowpack combined in 2015 to place a stress of Fraser River salmon due to lower discharge and higher temperature. This could be an issue in 2016 as well.

Kiwa Glacier in 2004 Google Earth image

2010 Image from Reiner Thoni. Well defined trimlines above the lake. Note flat lower section of the glacier.

Castle Creek Glacier is in the Cariboo Mts. of British Columbia. The glacier descends north-northeast for 6.3 km from 2825 meters to the terminus at 1,810 meters. During the last 50 years of retreat has left a series of annual terminal recessional moraines that indicate how much the glacier has retreated each year. The glacier has a remarkably uniform and relatively low slope for an alpine glacier. This is one feature that helps ensure that the retreat rate changes little from year to year as the glacier flow dynamics are consistent. There is no prominent icefall, there is no low slope terminus tongue that can stagnate. The extent of the glacier during the Little Ice Age is quite evident as the gray vegetation free zone. Castle Creek Glacier has receded every years since 1959 at total of 720 meters up to 2008, about 14 meters per year. The Universtiy of Northern Brictish Columbia as part of the Western Canadian Cryosphere Network has undertaken a detailed investigation of this glacier. Matt Beedle at UNBC has been the field leader for the project, and has had the chance to map and identify the annual recessional moraines. The three pictures below are from Matt Beedle. The first is a series of aerial photographs that have been cropped to show the same area. Note that in 1946 the glacier filled the view, by 2005 it barely makes the image. The period from 1971 to 1991 has the most notable recessional moraine ridges. Beyond the 1967 margin there are at least 10 moraine ridges
The recessional terminal moraines are not unusual features to be formed by a retreating glacier, however they are unusual to be formed each year and to be so well preserved. The recessional moraines are deposited on a till plain exposed by the glacier retreat. Often such moraines are ice cored and tend to disappear as the ice core melt outs, not the case here. The moraines form during the winter when the glacier continues to move and the terminus is not melting. In summer after the terminus area is exposed the terminus melts back. The Key as pointed out by Matt Beedle is summer temperature. Such moraines will not form on a glacier with a stagnant glacier tongue. Such moraines also do not form on glaciers that have a terminus area that is an avalanche runout zone that can bury the terminus some years.
The glacier fits the pattern of glaciers throughout the southern interior ranges of BritishColumbia and Alberta which Blch et al (2010) noted lost 11% and 25% of their area over the period 1985–2005 respectively.