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UNIVERSITY OF OSLO What is ”glacier surge” ?

• Surge is a dynamic instability i.e. the glacier is not able to establish steady state profile

• Sudden velocity change - transport of ice from reservoir area to lower part - advance of a glacier front

• Periodic phenomena – Quiescent – up-building period: 30-150 years

– Active – advance period: 2-8 years

• Velocity increase of 10-100 times

• Usually a front advance

• More than 100 surges observed in Svalbard

Continuity equation

x

xQ

x

xQ vb

)()(

x

xQ

x

xQ vb

)()(

x

xQ

x

xQ

t

xS vb

)()()(

Quiescent –upbuilding

periods:

• The geometry change:

• Up-building in the upper part

• Down-melting in the lower part

• Gradient gradually getting steeper

• Stable climate = stable periods

x

xQ

x

xQ vb

)()(

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Active surge period

Dynamical changes

• Velocity 2-5 m/day most common, but much higher

has been recorded - up to 100 m/d (Iceland) and 35

m/d in Svalbard

• Fastest on calving glaciers

• Calving glaciers advance more than glaciers ending

on land

• Calving glaciers may advance several kilometers

• High sediment fluxes

x

xQ

x

xQ vb

)()(

What triggers the surge ?

1. Critical value of the basal shear stress

t r g h sin a

2. Basal hydrology – water pressure

1. Switch in subglacial hydrological drainage

system from tunnels/channelized – to

distributed/linked-cavity system

2. Deformation of subglacial water-saturated till

Finsterwalderbreen Elevation difference 1970 – 1990

Longitudinal profiles – Kongsvegen t r g h sin a

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Kongsvegen – balance flux and volume flux

Balance flux

Volume flux

Balance flux gradient

Volume flux gradient

(a)

(b)

-0.2

0.0

0.2

0.4

0.6

Flux

gra

dien

t (1

0-4 m

2 a-1

)

0

1

2

3

Ice

flux

(106

m3 a-1

)

0 5 10 15 20 25

Longitudinal position (km)

Qv << Qb

Qb / Qv > 10

Subglacial drainage in quiescent stage

tunnel system (R-channels) pw low and

decrease with Q

(Hock & Hooke 1993)

Subglacial drainage during surge– distributed

linked cavity - pw is high and increase with Q

(Kamb 1987)

Water pressures/discharge in drainage systems

?

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Outburst floods from Grimsvötn,

Vatnajökull

Björnsson, 1998

Hydrographs

during surge and

during quiescent

Björnsson, 1998

Why so many surge-type

glaciers in Svalbard ?

• Polythermal glaciers:

• Low temperatures

• Low flow velocity

• Melting during summer give lots of water in the ice

• Low surface gradients

Temperature conditions in Svalbard

polythermal glaciers

Ground penetrating radar Lovénbreen

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Uværsbreen

temp and water

Calving and

surging glaciers in Svalbard

860 km calving front

(Blaszczyk et al. 2009)

UNIVERSITY OF OSLO

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UNIVERSITY OF OSLO

UNIVERSITY OF OSLO

UNIVERSITY OF OSLO

UNIVERSITY OF OSLO

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UNIVERSITY OF OSLO

UNIVERSITY OF OSLO

UNIVERSITY OF OSLO

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Usherbreen, surge push-moraines Paulabreen surge

• Paula_surge_stor_000.wmv

M. Sund

Ingerbreen 2001 - quiescent stage

ASTER 2001 2 km Sund, 2011 M. Sund

Ingerbreen 2005 - active surge

2 km ASTER 2005 Sund, 2011

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M. Sund ASTER 2005

Ingerbreen 1990 - 2003

569000570000

571000572000

573000574000

575000576000

577000578000

579000

86260008627000

86280008629000

86300008631000

86320008633000

8634000

-120

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

140

Elevation

change in

metres

Accuracy: ~ 20 m

2 km Sund, 2011

Nathorstbreen ALOS Palsar- before and after the surge

20080718 20090721

Surge on Nathorstbreen September 2009 (Trond Aagesen)

Nathorstbreen 2009-2011 ∆L ~ 20 km v> 20 m/d AAR pre/post surge: 0.71 / 0.37

Sund, 2011

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Partial surge Zawadskibreen, Svalbard

Sund, 2011

Austfonna - ICESat repeat tracks 2003-2008

Area:

~8000 km2

Calving-front:

> 200 km length

Moholdt 2011

Surge-type basins on Austfonna

1930s 1850s

1936-38

Austfonna area: ~8000 km2

Calving-front, all grounded : > 200 km length

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x

xQ

x

xQ bv

)()(

gradhuwb ssn

0t

h

gradhuwbt

hssn

Mass balance and ice flux

Entire accumulation area ( 5700

km2) Bn ~ 1 km3a-1

Ice flux Qv ~ 0,5 km3a-1

Large dynamic instability !

(From Bevan 2007)

Elevation change rates 2002-2008

Surge

basins

Moholdt 2011 InSAR ’velocities’ Dowdeswell et al., 1999

Basin-3

Basin-3: marine grounded & surge-type

A ~ 1200 km2

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Mid-1990s velocity structure & ongoing GPS observations

Dunse et al., 2012, (b) modified from Dowdeswell et al., 1999

ERS-1/2 InSAR

Single-frequency GPS unit (IMAU) • 5 stations; 2008 to present • operate unmaintained for 1 (3) years • Argos data transmission • meter accuracy

2011-2013 • mini-AWS (HOBO) • Trimble Dual-frequency GPS

GPS equipment on Basin-3

Basin-3

50-150% from ≤ 1 to ≤ 2 md-1

Duvebreen

0-50% from ≤ 0.5 to ≤ 0.8 md-1

Multiple velocity peaks follow prolonged melt periods renewed meltwater input

enhances basal lubrication

Summer speed-up 2008

2008 2009 2010 2011 2012 2013

m/d

7

5

3

1

Se s

Summer speed-up 2008 Dunse et al TCD 2014

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Stepwise acceleration coincident with the annual summer speedup 2008 - 2013

2008 2009 2010 2011 2012 2013

m/d

7

5

3

1

E

Stepwise acceleration coincident with the annual summer speedup 2008 - 2013

2008 2009 2010 2011 2012 2013

m/d

7

5

3

1

Stepwise acceleration coincident with the annual summer speedup

2008 2009 2010 2011 2012 2013 2014

m/d

7

5

3

1

10

m

150 m

Crevasses formation in upper reaches, after 2004

2004 2007

2008 2012

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Velocity pattern from TerraSAR-X

T. Schellenberger, UiO 0

1.2

2.4

3.6

4.8

6 m d-1

2250 m yr-1

Velocity pattern from TerraSAR-X April and August 2012

Velo

city (m d

-1)

Apr 2012 Aug 2012

T. Schellenberger, UiO

Velocity pattern in Basin-3 from TerraSAR-X

July 12 - 23 2014

T. Schellenberger, UiO

Total Svalbard archipelago

Ice-mass loss 4.2 ± 1.5 Gt yr-1

(6.2 ± 2.0 Gt yr-1 incl. rest of ASF)

Basin-3 calving flux Apr 2012 – May 2013

Geodetic mass balance −4.3 ± 1.4 Gt y−1

2003–2008 (Moholdt et al., 2010) Terminus retreat loss −2.3 ± 0.8 Gt y−1

(Blaszczyk et al., 2009)

Ice-mass loss 6.6 ± 2.6 Gt y−1

SLR contribution from Basin-3 alone is about that from the rest of entire Svalbard !!

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IPCC AR5 Modeled sea level rise 2100 0.26 to 0.82 m (incl. dynamics)

0.2 m

0.4 m

0.6 m

1.0 m

(from IPCC 2013, SPM Fig.8)

0.8 m

• Marine-based

West-Antarctic ice

sheet

• Several metres

• We do not know !

IPCC WGI Fig 4.18

Ice-sheet collapse (surge) – unlikely ?

Surge summary

Surge occur on both temperate and poythermal glaciers

Both marine and land-terminating glaciers surge Quiescent period varies a lot Active surge advance period varies a lot Hydrology is important - linked cavity during

active surge High sediment fluxes during surge advance Partial surge may occur

Surge processes are still challenging !

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Heidi Sevestre PhD project:

Global distribution of surge-type glaciers

ERA-Interim extracted for all glaciers centerpoint total precipitation 2m temperature

Cell size: approx. 70x70 km

Scatter plot

Climatic distribution of surge-type glaciers VS normal glaciers

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Differences in glacier area

* = significant difference (student t-test p= 0.05) Shading = sample size > 30

Why are some conditions not conductive to surging?

Concept of Enthalpy (Aschwanden et al., 2012) To maintain a steady state, a glacier must simultaneously find solutions to two problems: 1. Mass « balance » 2. Energy fluxes in and out of the system must balance to maintain constant enthalpy => both problems are tighly coupled.

1. If strain heating increases ice temperature / creates basal meltwater faster than it can be

dissipated -> positive feedbacks will cause the glacier to accelerate and flow above its balance velocities. 2. Conversely, if heat is dissipated faster than it can be generated by ice flow and geothermal heating -> the glacier will decelerate and ice will accumulate within the sytem.

Examples Why are some conditions not conductive to surging?

Cold, arid environments: Low balance fluxes and frictional heating -> low E production Dissipation by conduction. Except: larger glaciers

Warm environments: temperate glaciers High balance fluxes and frictional heating -> High E Dissipation by high basal runoff

Optimal surge envelope: Neither conduction nor runoff are efficient enough -> possibility of heating-velocity feedbacks at the bed