1. Jokulhlaup Geomorphology
Jokulhlaup/glacial terminology
Skeidararjokull Event

2. Jökulhlaup and Glacial Terminology
Warm-based glacier: MAT within a few degrees below 0oC, “temperate,” nearly isothermal, at pressure melting point
Cold based glacier: MAT greatly below 0oC, “polar,” T lowest at surface
Eskers: subglacial landforms. Deposited by interlobate glacial meltwater. Assoc with retreating glaciers; 10s-100km in length, few-50+ m high, s m wide
Progradation: lateral accretion of sedimentary interface
Aggradation: vertical accretion of sedimentary interface
Stoss Side: upcurrent side of a bed form
Foreset bedding: basinward dipping beds accumulating on a submerged slope.
(Terrestrial: frontal slope of delta, lee side of dune)
Hydraulic jump: local hydraulic instability of a current owing to sudden increase in thickness and/or change in gradient
Jökulhlaup: “glacier-run” Icelandic term for catastrophic flood from the collapse of an ice dam. Supraglacial, subglacial

3. Causes of Jökulhlaups Ice barrier bouyancy, ice dams a narrow valley
(Lake Missoula)
Pressure at base of glacier overcome by increasing pressure of subglacial lake (Grimsvotn)
Plastic deformation of barrier- supraglacial flow
Lake overtops glacial dam
Flow continues as long as channel enlargement is greater than rate of closure- typically end abruptly (hydrograph)
squeezing shut of channels
channel collapse
channel infill
bedrock cutoff
Repeated jokulhlaups are known for Skeidararjokull area from present

4. Glacial Lake Missoula 2500 km3 lake
Underflow subglacial tunnels catastrophic discharge
40+ silt to sand graded rhythmites

5. The Skeidararjokull Event
November 5 –

6. Vatnajökull icecap Grímsvötn caldera
A.J. Russell et al. Global and Planetary Change –216

7. A.J. Russell et al. Global and Planetary Change 28 2001 193–216

8. A.J. Russell et al. Global and Planetary Change 28 2001 193–216

9. A.J. Russell et al. Global and Planetary Change 28 2001 193–216

10. Jökulhlaup, 5 November 1996 at 1200
A view towards west across the central part of the outlet glacier, Skeiðarárjökull. The jökulhlaup burst through the glacier snout some tens of meters from the edge and followed the glacier moraine before finding its way out to the alluvial plain. The photo is taken ~1 hour after water started to emerge from this part of the glacier.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

11. Same time different view
Skeiðarársandur is covered with a thin layer of snow but the area under water appears dark. The main part of the flood is still in Skeiðará to the east.
The flood has just started in Gýgja, which appears as a narrow dark band in the central part of the plain. (Öræfajökull is the highest mountain in Iceland, 2119 m. The road across the plain is 35 km long)
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

12. The mouth of Skeiðará, 5 November 1996 at 1230
Note the turbulence in the jökulhlaup water which generates a surprisingly regular circle on the surface of the sea.

13. The mouth of Skeiðará
Note concentric rings – pulses of sediment related to rhythmites
in sedimentary infill in Gigjukvisl…?

14. Jökulhlaup, 5 November 1996 at 1430
A view towards north, showing the easternmost part of the jökulhlaup, the 900 m long Skeiðará bridge and the dike system protecting the Skaftafell National Park, which is situated to the east (right) of the river. At this time about 15,000 m³/s was flowing down this part of the alluvial plain. The bridge was still intact but a few hours later the easternmost end was washed away.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

15. Jökulhlaup, 5 November 1996 at 1300
The eastern end of the 380 m long bridge across Gýgja has disappeared. The total discharge in Gýgja at this time is close to 5,000 m³/s. This bridge was totally destroyed by the jökulhlaup.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

16. Post Jökulhlaup, 6 November 1996
Aerial photograph taken during the jokulhlaup waning stage at 1200 h on November 6, Embayment shape and nearby major ice fractures can be seen clearly.
A.J. Russell et al. Global and Planetary Change –216

17. Downstream, where the Jökulhlaup crossed Route 1

18. Grímsvötn and Grímsfjall, 7 November 1996
A view towards southeast across the Grímsvötn depression after it has subsided 165 m. The outlet from the lake is at its southeastern margin, i.e. to the left of the Grímsfjall mountain range.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

19. Grímsvötn viewed from the north, on 7 November 1996
Pressure ridges have formed over crevasses in the northern part of the depression. The temperature within the depression was -25 degrees Centigrade and fog has formed in the cold still air, aided by steam rising from crevasses.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

20. Closeup of the Grímsvötn outlet by the eastern rim of Mt
Closeup of the Grímsvötn outlet by the eastern rim of Mt. Grímsfjall, 7 November 1996.
The mountain cliffs are about 300 m high. Huge cauldrons formed at regular intervals within the 6 km long and 500 m wide outlet. The outlet canyon was formed during the flood on 5-6 November.
On 6 November flowing water could be seen at the bottom of the largest pit craters formed in the canyon where the roof over the subglacial outlet tunnel had collapsed.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

21. Southern part of the Grímsvötn outlet, 7 November 1996.
The glacier canyon is 6 km long and 500 m wide with an average subsidence of 100 m. Steam rises from the canyon.
These photographs were taken by Magnús Tumi Guðmundsson and Finnur Pálsson.
Copyright (C) 1996, Science Institute, University of Iceland. 08 November 1996

22. Post jökulhlaup
~Breccia of ice fragments fused into chamber walls indicate min estimate of max flow depths in eastern chamber
Eastern chamber backwall

23. May

24. During flow… After meltdown…
2 yrs

25. 500 m long 100 m wide ice walled supraglacial channel
Sedimentary infill deposited by discharges exceeding 20,000m3/s or 540,000 cfs.
(calc from x-sec A-A’ and B-B’) in west chamber and central channel
Ground Penetrating Radar grid in central channel
Outcrop sections 1, 2, 3 and 4 examined after retreat of ice.
Instances of four different hydrologic regimes during jökulhlaup
A.J. Russell et al. Global and Planetary Change –216

26. Ground Penetrating Radar (GPR) Survey
Thin armour surface
Well defined moderately angled (10 – 15o) high relief amplitude (15 – 20 m) upstream-dipping beds. (Indication of Froude #?)
Poorly sorted beds showing few signs of clast imbrication or clustering
Lg scale 1 – 2 m-thick cross-beds containing boulder-sized clasts
Laterally extensive alternating polymodal (matrix and clast) supported units

27. Outcrop Section 1 Bedded sand + gravel dipping to wall- eddy bar
Convolutions, soft sediment deformation, vertical pillars with gravels from lower beds
Upward movement of fluidized water + sediment
A dewatering structure
Highest surveyed point, dewatered first?
Seems to be a “lower” energy area…?

28. Outcrop Section 2 ~Highly variable dip of rhythmites
~Due to turbulent clockwise cell?
~High flow, but different to high flow in main channel
~Also relatively high ground as water resided

29. Outcrop Section 3 Similar to GPR section Down-channel dipping strata
Down-channel migration of high-relief bars
Bed thicknesses comparable to Pleisto-flood dunes
Super critical flows (high Froude #) during later stages of jokulhlaup
Thin armour surface

30. Outcrop Section 4 Terraced appearance, covered by rip-up clasts
Deposited supraglacially
2 lg cross stratified sections capped by erosional contact
Imbricated gravel unit above
Anticlockwise eddy in corner
Foreset bedding

31. Is this a new analog for eskers?
Was the mid and eastern US an area with high jokulhlaup activity?
Do we find jokulhlaups associated with other landforms usually associated with eskers?
Do we know enough about the sedimentology of eskers to compare them with this process?

32. 1998 eruption of Grímsvötn
Freysteinn Sigmundsson, 1998

33. References
Russel et al, Morphology and sedimentology of a giant supraglacial, ice-walled, jokulhlaup channel, Skeidararjokull, Iceland: implications for esker genesis
Russel et al, Sedimentary Architecture Of A Supraglacial Jökulhlaup Channel-fill, Skeiðarárjökull, Iceland.
Sigurdsson et al, The jokulhlaup on Skeidararsandur in November 1996: Event, discharge and sediment