Supplement of The Cryosphere, 9, 1183–1190, 2015http://www.the-cryosphere.net/9/1183/2015/doi:10.5194/tc-9-1183-2015-supplement© Author(s) 2015. CC Attribution 3.0 License.

Supplement of

Winter speed-up of quiescent surge-type glaciers in Yukon, Canada

T. Abe and M. Furuya

Correspondence to:T. Abe (abetaka@frontier.hokudai.ac.jp)

The copyright of individual parts of the supplement might differ from the CC-BY 3.0 licence.

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Supplementary material of “Winter speed-up of quiescent 1

surge-type glaciers in Yukon, Canada” by T. Abe and M. 2

Furuya 3

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This supplementary material documents the surging episodes at four glaciers (Lowell, 5

Tweedsmuir, Ottawa Glacier, and Logan). We show radar intensity changes associated with 6

the opening and closing of crevasses due to the surge; the intensity changes were derived by 7

the RGB method (Yasuda and Furuya, 2013). We also describe the spatial-temporal changes 8

in the ice velocity at the glaciers and terminus advances during their active phases. 9

1. Surface crevasse formation revealed by SAR intensity analysis 10

Due to the sudden speed-up, a glacier surge generates new crevasses that will dramatically 11

change the surface roughness and hence enhance the SAR scattering intensities (Yasuda and 12

Furuya, 2013). By co-registrating two temporally separated SAR intensity images and 13

assigning the older image (master) with cyan [(Red, Green, Blue) = (0%, 100%, 100%)] and 14

the newer image (slave) with red [(Red, Green, Blue) = (100%, 0%, 0%)], the composite 15

image tells us where the scattering intensity has remarkably changed. This is called the RGB 16

method, which has also been employed in identifying the emerged/subsided small islands 17

after the 2004 Sumatra Earthquake (Tobita et al., 2006). In the composite image, the cyan 18

shows areas having an intensity increase, whereas the red shows with a decrease. The RGB 19

method allows us to clearly visualize the intensity changes that can be attributed to the 20

initiation of glacier surge. Although the SAR intensities can change by other processes such 21

as surface melt in summer and snow accumulation in winter, we apply this method to the 22

intensity images before and after a significant speed-up event (i.e., surge episodes), which 23

occurred at Lowell, Tweedsmuir and Ottawa Glacier (Fig. 1). We have confirmed that there 24

are few changes except surging glaciers (i.e., non-surging glaciers and off-ice area). Thus, all 25

the intensity changes we show below are attributed to glacier surge. 26

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2. Spatial and temporal variability of surging glaciers 30

2.1 Lowell Glacier 31

Lowell Glacier is a famous surge-type glacier located in Kluane National Park near the 32

eastern edge of the St Elias Mountains. According to the Yukon Geological Survey (YGS), 33

Lowell Glacier has surged 5 times in the last 70 years (YGS, 2011). The latest surge began in 34

late 2009 and continued until late 2010 (YGS, 2011; Bevington and Copland, 2014). Pre-35

surge, the ice velocity was at most ~1 m/d (2007- 2009), it exceeded 5 m/d in the data pair of 36

January and March 2010 (Fig. S1). This is consistent with the YGS report. The ice velocity 37

slowed down in July and September 2010, but a lack of data prevents us from determining 38

exactly when the surge ended. 39

Figure S2a shows that the terminus advances by up to 4 km from early 2009 to July 2010. The 40

RGB method shows how the radar intensity increases after surge begins (Fig. S2b), and how 41

it decreases after the surge ends (Fig. S2c). We interpret the intensity changes as being due to 42

changes in the roughness of the ice surface that are attributable to the opening and closing of 43

crevasses at the start and end of the surge. 44

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2.2 Tweedsmuir Glacier 46

Tweedsmuir Glacier is 50-km south of Lowell Glacier in the St. Elias Mountains. According 47

to the United States Geological Survey (USGS), the last surge began around 2007 summer 48

and terminated in 2008 (USGS, 2010). Figure S3 shows the ice velocity evolution, which 49

exhibits a greater velocity with ~6 m/d during the period from August to October 2007, but 50

slows down in January to March 2009. In 2010, we find a summer speed-up, but the velocity 51

magnitude is ~0.3 m/d, which is an order of magnitude slower than that during the surge in 52

2007. 53

Figure S4a shows the terminus location changes, which expands several hundreds of meters 54

from the summer in 2007 to 2009. The RGB-method images in Figs. S4b and S4c, analogous 55

to those in Fig. 2 show the surge at its beginning and end. 56

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2.3 Ottawa Glacier - A tributary of Chitina Glacier - 60

Chitina glacier is a major surge-type glacier that forms the Chitina River Valley system. 61

Although surging episodes have been inferred from satellite image analyses (Clarke and 62

Holdsworth, 2002), we know of no ground-based monitoring at this glacier. 63

Figure S5 shows flow velocity at Chitina Glacier from the oldest at the top left to the most 64

recent at the bottom right. Starting in fall 2009, the velocity increases at the confluence 65

between Chitina and Ottawa Glacier (Fig. S5l). On Feb-Mar 2010, it speeds up to 4 m/d at 66

Ottawa Glacier (Fig. S5p-q), and we regard it as the active surging phase. Meanwhile, the 67

velocity in the upstream region of Chitina Glacier gradually increases as winter approaches 68

(Fig. S5k-o). In contrast to the surge, the winter speed-up occurs every winter, which thus 69

indicates that the wintertime acceleration in the upstream of Chitina Glacier is independent of 70

the surge at Ottawa Glacier. Moreover, the winter speed in the upstream region is comparable 71

to and sometimes higher than that in spring/early summer in 2010 (Fig. S5s), which we 72

believe had not been observed before. The higher speed in the middle to downstream (Fig. 73

S5q-t) may have been triggered by the surge at Ottawa Glacier. 74

The increase of radar scattering intensity coincides with the surge initiation (Fig. S6a). Later, 75

in summer 2010, the flow velocity changes (Fig. S5t). This indicates that Ottawa Glacier 76

underwent a surging episode that terminated around summer 2010. Figure S6b shows the 77

surge at the end. 78

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2.4 Logan Glacier 82

Logan glacier is also a major glacier that consists of the Chitina River Valley system. Figure 83

S7a shows the spatial and temporal changes in the velocity. In 2007 and 2008 winter, the 84

speed at 20 km point from the terminus is about 0.4 m/d. However, it is up to 0.8 m/d in 2010 85

and 2011. The winter speeds appear to increase from one year to the next. This is a clear 86

feature for surging. Figure S7b also shows the velocity increase year to year. Thus we 87

consider it as the initiation of a new surging episode. 88

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References 90

Bevington, A., and Copland, L.: Characteristics of the last five surges of Lowell Glacier, 91

Yukon, Canada, since 1948, J. Glaciol, 60(219), 113-123, 2014. 92

Tobita, M., Suito, H., Imakiire, T., Kato, M., Fujiwara, S., and Murakami, M.: Outline of 93

vertical displacement of the 2004 and 2005 Sumatra earthquakes revealed by satellite radar 94

imagery, Earth Planets Space, 58, e1–e4, 2006. 95

The United Nations Geological Survey: 96

http://ak.water.usgs.gov/Projects/Tweedsmuir/index.php, last access: 25 June 2013, 2010. 97

Yukon Geological Survey: http://www.geology.gov.yk.ca/821.html, last access: 24 May 2013, 98

2011. 99

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Figure S1. Surface velocity evolution on Lowell Glacier. The color scale is logarithmic. 131

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Figure S2. Surging event on Lowell Glacier. (a) Terminus locations based on PALSAR 155

intensity images. (b) An RGB composite image derived from the images on 3 March, 2009 156

and 6 March, 2010. The red region indicates where the scattering intensity has increased. (c) 157

A composite image derived from the images on 3 March, 2010 and 10 September, 2010. The 158

cyan region indicates where the scattering intensity has decreased. 159

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Figure S3. Surface velocity evolution on Tweedsmuir Glacier. The color scale is logarithmic. 184

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Figure S4. (a) Terminus locations on Tweedsmuir Glacier based on PALSAR intensity 209

images. (b) An RGB composite image derived from the images on 29 August, 2007 and 14 210

January, 2008. (c) A composite image derived from the images on 29 February, 2008 and 16 211

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Figure S5. Surface velocity time-series (from upper left to lower right) at Chitina Glacier. 236

Images are arranged in the order of middle date between the first and second acquisitions for 237

each pair. The color scale is logarithmic. The black ovals mark a surge from autumn 2009 to 238

summer 2010 on Ottawa Glacier. 239

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Figure S6. Composite images on Ottawa Glacier. The larger glacier at the top is Chitina 257

Glacier. (a) An RGB composite image derived from the images on 23 December, 2008 and 26 258

December, 2009. (b) A composite image derived from the images on 26 December, 2009 and 259

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Figure S7. (a) Spatial and temporal evolution of the ice velocity profile along the flow lines of 283

Logan Glacier. The flow lines are marked in Fig. 1. (b) Averaged time-series plot at the 284

section between 18 and 21 km. Cyan shades stand for winter season (Sep - Feb). 285