Glacier surging. Susitna Glacier, Alaska (AusAn Post) Glacier surging McCarthy Summer School, 2016 Gwenn Flowers, Simon Fraser University

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1 Glacier surging Susitna Glacier, Alaska (AusAn Post)

2 Glacier surging: overview DefiniAons DistribuAon of surge- type glaciers ObservaAons QualitaAve characterisacs QuanAtaAve measurements Surge trigger(s) and mechanism(s) Underlying controls Departures from standard model htp:// naaonal- park- glacier- tour- day- trip- yukon/ Klubbebreen south, Svalbard (M Sund) Lowell Glacier, Kluane NaAonal Steele Park Glacier, Yukon

3 Glacier surges Internally- driven, episodic flow variaaons marked by 10- to 100- fold increases in flow speed [e.g. Meier & Post, 1969; Kamb et al., 1985] Dusty Glacier, Yukon Territory (G. Clarke) Triggered by fricaonal (thermal, hydrological, mechanical) transitions at the glacier bed [e.g. Kamb, 1987; Clarke et al., 1984; Fowler, 1987; Murray et al., 2003; Sevestre & Benn, 2015] [A surge] is different from a real advance of a glacier, which is caused by an increase in the volume of ice. (BBC, 1 Dec 2009)

4 Glacier surges Rapid flow acceleraaon moves mass from reservoir area downstream (surge) AcceleraAon due to enhanced basal flow: u b = u b ( b,p w ) z x Surge cycle requires the development of an ice reservoir, thus resistance to ice flow during quiescence.

5 Observed velocity compared to balance velocity Clarke, 1987 balance velocity observed velocity

6 VerAcal velocity anomalies Example: sustained vs episodic fast flow in Barnes ice cap Modelled surface speed Gilbert et al., in revision Normal velocity anomaly (difference between observed and expected elevaaon changes, )

7 Geographical distribuaon of surge- type glaciers Sevestre & Benn, 2015

8 Iceland NASA MODIS image Björnsson et al., 2003

9 Svalbard Jiskoot et al., 2000 Svalbard surges: return interval: yr duraaon: 3-10 yr

10 Alaska, Yukon, BriAsh Columbia Post, Journal of Glaciology, 1969

11 ObservaAons: qualitaave characterisacs Dusty Glacier (surge- type), Yukon Territory (G. Clarke) Kaskawulsh Glacier (not a surge- type glacier), Yukon Territory (G. Clarke) Strongly contrasang flow behavior between glaciers

12 ObservaAons: qualitaave characterisacs St. Elias Mountains (A. Post) Asynchronous behavior not clearly related to climate forcing

13 ObservaAons: qualitaave characterisacs Looped moraines: geomorphic evidence for pulsing flow Yanert Glacier, Alaska Range (A. Post)

14 ObservaAons: qualitaave characterisacs Looped moraines Black Rapids Glacier, Alaska (USGS)

15 ObservaAons: qualitaave characterisacs Looped moraines Susitna Glacier, Alaska (NASA Earth Observatory)

16 ObservaAons: qualitaave characterisacs Extensive crevassing Síðujökull surge, Vatnajökull, February 1994 (H. Björnsson)

17 ObservaAons: qualitaave characterisacs ChaoAc crevassing Hagafellsjökull surge, Langjökull, 1998 (H. Björnsson)

18 ObservaAons: qualitaave characterisacs Surge- front propagaaon Síðujökull surge, Vatnajökull, 1994 (H. Björnsson)

19 ObservaAons: qualitaave characterisacs Surge- front propagaaon Trapridge Glacier, Yukon (Clarke et al., 1984)

20 ObservaAons: qualitaave characterisacs Rapid advance Síðujökull surge, Vatnajökull, February 1994 (H. Björnsson)

21 ObservaAons: qualitaave characterisacs Evidence of distributed subglacial drainage Síðujökull surge, Vatnajökull, March 1994 (H. Björnsson)

22 ObservaAons: qualitaave characterisacs ProjecAon of bed topography to surface Tungnaarjökull in Vatnajökull, November 1994 (H. Björnsson) High raaos of basal moaon to deformaaon result in the projecaon of bed topography at the glacier surface

23 ObservaAons: qualitaave characterisacs ProjecAon of bed topography to surface Dyngjujökull surge, north Vatnajökull, 1998

24 ObservaAons: quanataave measurements Reservoir and receiving areas, Dyngjujökull, north Vatnajökull (Björnsson et al., 2003)

25 ObservaAons: qualitaave characterisacs Mass transfer from reservoir to receiving areas before Jul 1982 aper July 1983 Kamb et al., 1985

26 ObservaAons: measured velociaes and lateral shear margins Kamb et al., 1985

27 Surge trigger: switch in basal drainage system Slow system Fast system Kamb et al., 1985 Diagrams courtesy of T. Creyts

28 Surge trigger: return interval CumulaAve mass balance, Variegated Glacier, Early surge onset 1995 surge terminated prematurely aper two hotest days ever recorded in nearby Yakutat (Eisen et al., 2005) Harrison et al., Journal of Glaciology, 2008

29 Hydrological surge mechanism for temperate glaciers B. High ice discharge reduces glacier thickness, thus basal drag C. Low velociaes allow channel formaaon, water escapes A. High sliding velocity traps water under the glacier by suppressing channel formaaon D. Glacier thickens, increasing gravitaaonal driving stress and basal drag Aper Fowler (1987) in van der Veen (1999)

30 Hydrological surge mechanism for temperate glaciers Inferred evoluaon of basal fricaon prior to and during the surge of Variegated Glacier Jay- Allemand et al., 2011

31 Surge mechanism for polythermal glaciers Murray et al., 2003 Clarke et al., 1984

32 Underlying controls: climate? High Mountain Asia ArcAc ArcAc Canada Sevestre & Benn, 2015

33 Underlying controls: geometry, topography? CorrelaAon between surge tendency and slope can be explained by surge tendency length correlaaon and length slope correlaaon. Clarke, 1991 Sevestre & Benn, 2015

34 Underlying controls: geology? MulAvariate analysis of surge- type glaciers in Svalbard Variable is significant at 95% level Jiskoot et al., 2000

35 Underlying controls: geology? Surge- type vs non- surge- type glaciers disanguished by sediment size in metasedimentary basins and mineralogy in mixed lithology basins: sediment size sediment mineralogy 0.4 PC1 = 67.5% PC2 = 22.4% 0.2 load log (grain size)(mm) 2 Glacier type Metasedimentary non-surge (MS-NS) Metasedimentary surge (MS-S) Mixed non-surge (MX-NS) Mixed surge (MX-S) Geology Metasedimentary Granodiorite Crompton & Flowers, 2016; unpublished data from Crompton, SFU Glaciology Group

36 Alaska, Yukon, BriAsh Columbia Post, Journal of Glaciology, 1969

37 Alaska (Western & Central Ranges, Hayes Range, Delta Mountains) Herreid & Truffer, 2015

38 Climate, mass balance and the future of surging glaciers Slow surge of Trapridge Glacier (Frappé & Clarke, 2007) Vernagxerner advancing, 1844 (aper Thomas Ender, see Hoinkes, 1969) Björnsson et al., 2003 Tributary surges in Panmah Glacier, Karakoram Himalaya (HewiT, 2007)

39 Summary Glacier surges: last months to a few years have return intervals of years to decades open begin in winter are usually accomplished predominantly by basal moaon require warm- based ice or substrate (N but not S) require inefficient drainage systems (N but not S) appear to be of two types (temperate vs polythermal) are influenced but not driven by climate appear linked to glacier geometry/topography, climate/ environment, thermal structure, geology are changing with climate Photo: Tweedsmuir Glacier, 2008