Dynamics and Modelling of Glacial Systems

Oral exam with written preparation for 4 theoretical questions from the course material. Also an oral exam with the assistant with questions about theory / methods / assumptions / results of practicals.

The exam takes 1hr 30minutes: 30' for preparation of the theory, 30' oral questioning on the theory, 30' on-the-spot questions about the practicals

2024-2025

June

Theory

Theory worked with 4 series:

Series A

- Give the components of the energy balance of the surface of an ice sheet and explain them. How can we model these components and what assumptions do we use to do so?

- Explain using cases how gravity can invoke a horizontal flow in an ice sheet

- Surging glaciers: what are they? What is the proposed mechanism for the Variegated glacier in Alaska?

- What would be the effects of Greenland melting on relative sea levels in the near- and far-field? What mechanisms would drive this?

Series B

- explain different crevasse forms and patterns using their stresses

- explain link between basal pressure and sliding velocity, how can basal pressure be measured???

- what is the role climate regimes on specific mass balance gradient with elevation

- explain lagrangian and eulerian approaches to date ice, differences and advantages

Series C

- pdd paradox: why does it work when it shouldn't

- hydr gradient and subglacial lakes

- If you wanted to find the oldest ice in Antarctica, where and how would you go looking?

- Polythermal glaciers: structures (met grafiekje of ni?)

Series D

- WAIS - MISI?

- kut vialov rotvraag

- polarized light - why use it and why do some crystals appear black?

- subglacial drainage patterns & link to surging

Series E

1. Leg proces uit van sneeuw naar ijs, namen fasen

2. Why do ice shelfs flow and how do they deform, even with a horizontal surface.

3. Iets met hoe temperatuur reconstrueren met boreholes, dus wat kan de temperatuur van zo’n ice core ons vertellen over het verleden.

4. Iets van relative sea level change, hoe de dikte van icesheets uit het verleden gereconstrueerd kan worden. En wat de grootste uncertainty’s zijn.

Practical

Questions possible on all three practicals + the numerics. This part sucked ass - you needed to know formulas by heart that you didnt even need to know for the theoretical part. Examples of questions:

- Give the mass balance profile for Antarctica & Greenland

--> how would it change with a different ice albedo?

- give the energy balance equation's ablation component we used, with units, and explain

- what scheme did we use to calculate slopes? give formula+name+how big is the error?

- cfl condition - how to ensure stability?

- random ass graphs from the reports, without axes or labels: what is displayed here? what should the axes labels be? (these really fucking sucked)

2022-2023

Reeks 1

1. Glaciers experience gravitational flow. How does it come that they flow horizontally if gravity is a vertical component? Explain schematically how gravitational processes can induce a horizontal flow of a glacier.
2. How does the length of a glacier react to a sudden change? how can we calculate the new length? How can we calculate the volume response time?

• Why is the mass balance a function of x? b(x)?
• Why do we have a negative sign in the formula: ; if we increasing the length? This is because  (=smb at the terminus) is negative.

1. What are surging glaciers? Which mechanical process is dominant for the surging of the variegated glacier (Alaska);

• you had to explain that during a surge, it causes high pressure whereby the subdrainage systems (more specifically the channels) get closed off whereby it takes much more time to drain.

1. Explain how the relative sea level would change, when the whole Greenland ice sheet would melt, in near and far regions? What are the main mechanisms causing this

• What is geoidal-eustasy, and what is hydro-eustasy?

Reeks 2

1. Why is the West Antarctic ice shelf unstable? Will it collapse? Describe the instability of the WAIS invoking the concept of a 'flowline'.

• He also asked why it is stable with a normal slope.

1. How does climate affect the specific mass balance of glaciers?
2. Why do glaciologists use polarised light?

• You also needed to explain why a crystal appears black: this is when the c-axis is parallel to the vertical polarizer
• Explaining Schmidt diagram further and you had to show with your pen on the diagram how each crystal is oriented (in the middle of the diagram, pen was perpendicular to the dot)

1. Which subdrainage systems do you have under an ice sheet? How do they influence surging?

• He asked why the drainage system changes exactly (due to increasing ice overburden pressure)

Reeks 3

1. Explain the surface energy balance by the fluxes. Which is the most dominant? How did we model this?
2. What is the dynamic response time of sea ice, glaciers and ice sheets? Why do (East-) Antarctica and Greenland have different response times?
3. How can we date ice cores? There was also something like, describing both numerical and analytical approaches

• He shifted the question towards the Lagrangian-Eulirian techniques, their pros and cons, and an example of Kohler ice core we discussed in class (2 biases that it has)

1. Explain regelation. Has it a significant impact on basal sliding?

Reeks 4

1. How is a simplified case of the hydraulic potential calculated and which assumptions do you make to come to this solution? How does this relate to the capacity of a glacier to store water below the ice?

• Under which circumstances can water be hold on in subglacial lakes

1. Explain why the PDD model is paradoxical and how it is possible that it is still a good approximation?
2. What are polythermal glaciers? What types are there and explain all processes that determine their temperature distribution?
3. What conditions do you need for an ice core to contain old ice at a reasonable resolution? Where would you find such conditions?

WPO – Exam

1. First assignment (we had Antarctic ice sheet):

• Draw the SMB over the entire profile of the ice sheet
• How is an ice sheet constructed?
• Why does the Antarctic ice sheet not build up infinitely long if we only have an accumulation zone à this is because of the boundary condition
• What are the boundary conditions

1. Second assignment, still the Antarctic ice sheet

• Draw the temperature distribution along the ice divide.
• What are the boundary conditions
• Where does vertical advection play a dominant role à draw the temperature profile at the divide if there was only vertical advection and when there would be no vertical advection
• How can we assess the accuracies of the different schemes?
• Which variables did we change and what are the effects?
• What is internal diffusion?
• How does the temperature distribution look like when you have a larger SMB

1. Third assignment (Morteratsch glacier)

• How did we derive the precipitation and temperature along the glacier if we only knew it for one point/altitude?
• What is p-ratio
• Give the surface energy balance
• How does the energy balance profile look like across a year when a year starts in October and ends in September
• What determines the albedo?
• What are the constants and variables in this energy balance?

2019-2020

1. What components are in the surface energy balance of the earth? Give the expression + how are the different elements determined/modelled? What assumptions have to made in modelling?

2. What is relative sea level change + underlying factors? Give examples. What can lead to uncertainty when modelling?

3.  How can the temperature of the ice in a bore hole tell you something on the pas climate?

4.  Explain regelation

2017 - 2018

Series A

1. Explain the different components of the surface energy balance.

2. How does an ice shelf flow? When is it in equilibrium?

3. How to derive past climate information from an ice core?

4. Explain regelation.

Series B

1. How does the length of a glacier react to a sudden change? how can we calculate the new length? How can be we calculate the volume response time?

2. Explain the different modes of crevasses.

3. What are the different processes that lead to the transition of snow to ice?

4. What are balance velocities? How are these calculated? What input data are needed? What are patterns of balance velocities in Antarctica and Greenland.

Series C

1. What is the influence of the water pressure on the basal sliding of a glacier?

2. Explain the Positive Degree Day Model, why is it paradoxal?

3. Explain the different types of polythermal glaciers.

4. Eulerian vs. Lagrange

Series D

1. Describe the instability of the WAIS invoking the concept of a 'flowline'.

2. What are 2 non-climatological biases from the Kohnen ice core? What are their magnitues?

3. Describe how the assumption of perfect plasticity can be used to derive a surface profile for an ice shelf. Why is this not realistic?

4. Why do glaciologists research thin ice layers under polarised light? Discuss the mechanism and what physical properties can be derived from it?

2015 - 2016

10/6

09 AM-10.30 AM

1. How does the lenght of a glacier react to a sudden change? how can we calculate the new length? How can be we calculate the volume response time?

2. How can we reconstruct and model the ice load on the land with the relative sea-level changes? Explain how these models work, what the imputs are and what the highest uncertainty in these reconstructions.

3. What are the different processes that lead to the transition of snow to ice?

4. What are balance velocities? How are these calculated? What input data are needed? What are patterns of balance velocities in Antarctica and Greenland.

11.00 AM - 12.30 AM (same questions as 2013-2014 reeks 2)

1. Energy Balance

2. How measure tempeature differences from the past in ice cores?

3. Dilatation

4. Langrangian vs Eulerian

14.00AM-15.30 AM

1. Describe the instability of the WAIS invoking the concept of a 'flowline'.

2. What are dynamic response times for sea ice, glaciers and ice sheet? Why is there a difference between Greenland and Antarctica?

3. Describe how the assumption of perfect plasticity can be used to derive a surface profile for an ice shelf. Why is this not realistic?

4. Why do glaciologists research thin ice layers under polarised light? Discuss the mechanism and what physical properties can be derived from it?

17/6

1. 3 modes van crevasses (spleten) + uitleggen

2. Wat zijn de effecten van de eustatische zeeniveau na volledig smelting van Antarctica? Wat zijn de hoofdmechanismen van dit?

1. Explain the depth-age relation in ice cores? Discuss the 2 different approaches. What is the problem with one of them? Is the approach suitable to derive ages from the GRIP ice core? Why (not) ? (bij die laatste vraag moet je bijvertellen dat de accumulation niet constant is, tijdens de ijstijden was deze minder, waardoor een afwijking ontstaat).

2. The PDD approaches mass balance of a glacier with temperature. Seen the surface energy balance of a glacier this is a paradox. Explain.

3. What are polythermal glaciers? Give all the possible kinds. (All 6 figures) and explain. Where do they occur?

4. How does water pressure influence basal sliding? How do we apply this in a flow law?

1. What are the main type of subglacial drainage systems? Why are they important regarding surging glaciers?

2. Describe/Derive the Vialov solution for ice thickness. Which assumptions are made? Is it realistic?

3. The mass balance is dependent on the climate. Why? Explain why the mass balance gradient will change if the same glacier was located in a warmer climate.

4.  What are 2 non-climatological biases for the Kohnen station. What is their magnitude?

Practicum

Exercise 1 (ice flow): How did the ice sheet evolve from zero ice thickness to steady state, draw this? When is ice flow large enough (i.e. what variables control it)? What parameters did we change in the practicum and how is the ice sheet profile affected?

Exercise 3 (mass balance): Discuss the simple energy model. Which variables control it? Which parameters did we change in the exercise to evaluate model sensitivity? Draw the cumulative mass balance and how did a change in transmissivity, snow albedo and ice albedo affect the evolution during the year? Was there a trend in MB noticed over the years and is this different at higher vs. lower elevation on the ice sheet?

- how does the ice sheet builds up on the bedrock (first assignment: starts in accumulation zone and when big enough, flows towards ablation zone)

- assigment 3: how do we acccount for ablation? Explain effect of albedo, transmittance of atmosphere... How does PDD works and why?

2014 - 2015

1. Discuss 2 analytical methods that describe the relation between the depth and the age of an ice core. What are their assumptions and restrictions? Do both methods work well?

2. Explain PDD model and why does this work?

3. What is the relation between the sliding speed of a glacier and the pressure of the basal water.

4. Discuss the climatological and physical differences between Greenland and Antarctica, and when were both ice sheets permanent?

2013 - 2014

1. What is the stress deviator tensor? Why is this used?

2. Discuss 2 analytical methods that describe the relation between the depth and the age of an ice core. What are their assumptions and restrictions? Do both methods work well?

3. What is the relation between the sliding speed of a glacier and the pressure of the basal water.

4. Discuss the climatological and physical differences between Greenland and Antarctica.

Starting from when are both icecaps permanent?

1. Dilatation

2. Langrangian vs Eulerian

3. How to measure temperature differences from the past in ice cores

4. Energy balance of the ice sheet (You had to give ALL the formulas!)

Previous years:

1. Describe 2 methods to determine the thickness of ice sheets in depth. On which assumptions

are they based?

2. Discuss the climatological and physical differences between Greenland and Antarctica.

Starting from when are both icecaps permanent?

3. Explain the hydraulic potential, completely. What are the assumptions? How does water flow

in a glacier. Something about subglacial lakes …

4. Explain hydrate clathrate.

5. Why do we observe thin slices under the microscope? What physical processes can be

determined from that?

6. Something about the bore hole (from the last chapter). What non-climatological corrections

need to be taken into account and what are their magnitude?

7. Explain the Vialov solution. What assumptions were made and how are those realistic?

Discuss also the zero-order solution.

8. Discuss the physical parameters that form the hexagonal structures in ice crystals.

9. Until what depth are seasonal temperature variations visible in the ice profiles? What is the lag

time between the peak in temperature’s optimum and the peak of the perturbation in the ice?

10. What is “regelatie” (refreeze in dutch) and discuss the effect of ice flow.

11. Discuss all the stresses that occur on an object in 3D + drawing. How many components are

there? How many of those components are independent?

12. How does water pressure influence basal sliding? How do we apply this in a flow law?

13. How can we reconstruct the ice load on the land with the relative sea-level changes? Give

some mechanisms that control the relative sea-level change on a specific place. Draw a few

graphs from several places. What is the highest uncertainty for this kind of reconstructions?

14. Something about the “complete plasticity” and the profile of an ice shelf. Why is this

assumption not correct?

15. What are the most important subglacial drainage systems and what is their role in the dynamic

of surges?

16. What is dilatation? What is this for ice?

17. What is local mass balance? How can it be measured thanks to stakes? (give formulas and

explain, based on what principle, …)

18. Something about simple shear…

19. What is depth hoar ? What are the physical properties and how does it arise ?

20. What should we except regarding relative sea-level rise in the far field and near field for the

melting of Antarctica ? (explain all kinds of isostasy and eustasy)

21. Explain the hydraulic potential. How is this used in the glaciology? What are the assumptions

to use hydraulic potential? How can it be used to explain the occurrence of subglacial lakes?

22. What is the stress deviator tensor? Why is this used?

23. What 2 non-climatological biases can be distinguished for the dating of ice core in Kohnen?

24. Why do glaciologists research thin ice layers under polarised light?

25. Discuss 2 analytical methods that describe the relation between the depth and the age of an

ice core. What are their assumptions and restrictions? Do both methods work well?

26. Give all components that indicate the stress in one point in 3D. Give all components in the

right place on a sketch. How many independent components are there?

27. What is the relation between the sliding speed of a glacier and the pressure of the basal

water.

28. Explain the energy balance at the surface of a glacier. How can this be parameterized?

29. Explain Lagrange and Eulerian + possible problems.

30. What is the response time for ice sheets, glaciers and sea-ice? Give formulas and the

comparison between Greenland and Antarctica.