Lecture 3: Glacier hydrology

Question 1

The hydrological regimes of snow covered and glaciated catchments are similar in that, from December to March, groundwater discharge is equal to total discharge. What however, is the main way in which they differ?

Answer 1

Snow covered catchments do not have a glacial component of discharge, by which icemelt, firnmelt and snowmelt contribute a significant proportion of the discharge of glaciated catchments from June to October.

Question 2

Water flow is governed by variations in hydraulic potential. How is this determined at the surface compared to subsurface?

Answer 2

Surface hydraulic potential governed by elevation.
Sub-surface determined by elevation and water pressure (from the size/shape of conduit and pressure and density of overlying ice).

Question 3

Where are the supra-, En-, Pro- and Sub- glacial environments found on a glacier?

Answer 3

Supra = surface
En = in
Sub= beneath ice
Pro = in front of ice

Question 4

Name two features of the supraglacial environment.

Answer 4

Cryconite holes / ice carved streams

Question 5

By what feature does water leave the supraglacial environment for the englacial?

Answer 5

Moulins

Question 6

How does water flow into the proglacial environment?

Answer 6

Via release of subglacial water and throughflow of surface melt.

Question 7

Describe the flow in proglacial environments.

Answer 7

Flows through unconfined material and braided, dynamic channels.

Question 8

What is Bulk meltwater monitoring?

Answer 8

Annual/seasonal hydrograph or chemograph reveals drainage system.

Question 9

Describe the use of hydrochemistry.

Answer 9

The chemical composition of bulk meltwaters used to infer chemical weathering environment and therefore the hydrological flow path.

Question 10

Describe the 3 key features of dye-tracing.

Answer 10

• Known quantity of dye injected into moulin/crevasse
• Dye concentration monitored in BMW
• Hydrograph of water velocities plotted from dye return.

Question 11

What would a return curve of fast velocities show about the hydrological system? What would double peaks show?

Answer 11

• fast return = pressure and free flow in main conduits.

- Double peaks = braided conduit.

Question 12

Borehole investigations allow the subglacial drainage system to be measured directly, but how are they carried out?

Answer 12

• Boreholes drilled into glacier bed using hot water / steam drill.
• Sensors installed
• Borehole waters samples
• Dye traces conducted

Question 13

When is it easiest to investigate ice caves and why is this a problem?

Answer 13

Easiest to measure after glacial lake outburst but very dangerous.

Question 14

As expected, what is the pattern of variation in borehole water level though the glaciers depth?

Answer 14

Variation increase in frequency and magnitude towards the ice surface.

Question 15

What can variations in subglacial water pressure lead to?

Answer 15

Till deformation

Question 16

As BMW issues from the front of a glacier, what can its filtrate be analysed to make qualitative statements about?

Answer 16

Concentration of ions in BMW allows us to infer is the environment is sediment rich, if water has had long contact with the rock, or is open to atmosphere. (Supra/en glacial environments = less contact with rock)

Question 17

Name two features of the englacial system.

Answer 17

Conduits and water veins in ice.

Question 18

Give the three dualisms present in the potential properties of the subglacial system.

Answer 18

‘hard’ or ‘soft’ beds
Completely / partially filled conduits
Distributed or channelized drainage.

Question 19

What is used to measure dye concentration and how does it work?

Answer 19

Fluorometer - light shined on fluorescent dye particles (reflected?) relative to concentration.

Question 20

Describe the properties of distributed and channelized drainage systems.

Answer 20

Distributed - low, steady discharge. Covers large area of bed relative to volume.
Channelized - Adapted to high discharge and can cope with big variations. Has a small bed relative to volume and efficient drainage.

Question 21

Decide if whether each of the following is an example of a distributed or channelized drainage system:
Linked cavity systems, canals, Rothlisberger channels (upcise into ice), water film, Nye channels (water dissolves rock) and flows through porous sediments.

Answer 21

Distributed = water film, linked cavity system, flow through porous sediments, canals.
Channelized = nye (water dissolves rock) and rothlisberger (upcise into ice).

Question 22

Is the following likely to be an example of a channelized or distributed drainage system? :
A canal incised into overlying ice, with an arterial flow path, carbonation of rock flour and shut down over winter.

Answer 22

Channelized

Question 23

How does weathering and residence time vary between channelized and distributed drainage?

Answer 23

• Channelized drainage systems have shorter residence times.
• Weathering of reactive minerals (+carbonation of rock flour) occurs in channelized drainage systems, whilst distributed drainage systems weather less reactive minerals (such as silicate-bearing bedrock)

Question 24

How might subglacial water be released infront of a glacier?

Answer 24

Via subglacial portals or proglacial upwellings.

Question 25

Describe the Geodetic method of observing mass balance.

Answer 25

Repeated photogrammatic study of glacier over 5-10yrs at near to identical min. snow conditions.

Question 26

What dominates discharge in the alps, and what does this show are the controlling features?

Answer 26

Meltwater runoff - therefore heat fluxes and surface energy balance are the controlling features.

Question 27

At what rate does precipitation fall, as snow increases with elevation?

Answer 27

2.5 - 3.5% per 100m

Question 28

What is the general effect of precipitation on runoff?

Answer 28

negative, as solar radiation lower and new snow has very high albedo.

Question 29

Where do moulins and crevasses occur in the alpine drainage system?

Answer 29

• In the middle generally. At the bottom of the distributed system, before channelized/conduit system begins.

Question 30

Describe the evolution of a drainage system in the early season.

Answer 30

Extensive snow cover, fills crevasses and moulins. Small melt input, with distributed system at max extent.

Question 31

How does the drainage system evolve in the mid-late season?

Answer 31

Snow line retreats, increased ablation rates, high and very variable discharge, channelized system grows at the expense of distributed.

Question 32

What happens to the ratio of daily min:max flow as basin/glacier size increases?

Answer 32

ratio decreases due to increasing base flow

Question 33

The diurnal runoff cycle overlies the whole basin. What forms the ‘base flow’ of the basin?

Answer 33

Runoff from groundwater, firnwater aquifers, storage zones and lake drainage.