G&H3: Hydrology

Question 1

3 reasons why glacier hydrology is important?

Answer 1

1. glacier fed rivers provide large % of agriculture water supply
2. hydropower
3. potential hazard

Question 2

What are the inputs to the glacial hydrological system?

Answer 2

Snow, rain, valley-side runoff, surface melt, basal melt

Question 3

What are the two storage types of the glacial hydrological system?

Answer 3

1. snow and ice

2. lakes

Question 4

What are the 3 transport types of the glacial hydrological system?

Answer 4

supraglacial channels
englacial conduits
subglacial drainage

Question 5

What is the relative permeability of snow, firn and ice?

Answer 5

snow = highly permeable
firn = permeable
ice = inpermeable

Question 6

What is a way to think of how permeable firn is and how this affects its storage/

Answer 6

It is like a slush puppy

Question 7

Because ice is impermeable, what does this cause overlying water to do

Answer 7

it becomes runoff that will incise supraglacial channels and consequently infill supraglacial lakes

Question 8

What is hydraulic potential?

Answer 8

The pressure/power of the hydrology like how powerful the water body is

Question 9

How does water flow with hydraulic potential?

Answer 9

Water flows down lateral gradients of hydraulic potential. It will flow down the steepest slopes of hydraulic potential and will also flow fastest down these areas

Question 10

How are supraglacial lakes formed?

Answer 10

the surface runoff will collate in an ice surface minima where the inflow>outflow. As the inflow is greater the lake will consequently keep growing in area

Question 11

What can happen once a supraglacial lake grows big enough that it encounters a crevasse in the surface?

Answer 11

the lakes can drain very quickly if they encounter a crevasse because it is essentially a weak point in the ice and so if the pressure from the ever-increasing water body grows then this crevasse will collapse forming a vertical drain from the surface down below.

Question 12

What is the name given to a vertical drain from the surface down to a crevasse?

Answer 12

Moulin

Question 13

What is the name given to the process of vertical draining through a moulin and what does it involve?

Answer 13

hydrofracturing - as the water drains quickly through the moulin the ice the friction against the ice will cause greater melting and stretching of the drainage hole

Question 14

What are some possible drainage destinations from a moulin?

Answer 14

glacier base, englacial channels, conduits

Question 15

Why is there uncertainty regarding the routing of drained supraglacial water?

Answer 15

Because we are unable to access the base of the glacier safely and so conducting investigations is less easy

Question 16

What study is much of the minimal knowledge regarding englacial/subglacial processes inferred from?

Answer 16

Shreve (1972)

Question 17

What did Shreve (1972) state?

Answer 17

1. englacial drainage systems are in a steady state where by glaciers are constantly trying to close up on themselves but the glacier hydrological flow is resistant against
2. englacial water flows along the steepest hydraulic gradient
3. pressure head (the pressure on the walls flowing through the channels) is the pressure of surrounding ice of channels minus melting of walls

Question 18

Where have most investigations in to englacial/subglacial processes been focused?

Answer 18

Svalbard

Question 19

What key component changes between supraglacial and supraglacial environments?

Answer 19

Presence of ice overburden pressure

Question 20

What is the ice more likely to reach as a result of the greater pressure exerted upon it?

Answer 20

Pressure melting point

Question 21

What do we assume the pressure of the water at the base of the ice to be?

Answer 21

The ice overburden pressure

Question 22

What can sometimes happen to water as a result of the overburden pressure which would usually be regarded as unusual?

Answer 22

The water can flow uphill

Question 23

Where would upward flowing water at the base of the glacier most commonly be found and why?

Answer 23

further away from the glacier outlet because closer to the glacier outlet means that the ice thickness decreases and so the overburden pressure also does

Question 24

What can a relic upward flowing channel tell us about past glacial landscapes?

Answer 24

that the ice was of a great enough thickness to cause water to flow upwards

Question 25

What are the two types of subglacial drainage?

Answer 25

Channelised and distributed

Question 26

What are the two types of channelised subglacial drainage?

Answer 26

Rothlisberger channel and nye channel

Question 27

What are rothlisberger channels and how are they formed?

Answer 27

They are channels that have been created by erosion in to the base of the ice as a result of the ice overburden pressure subsiding enough to allow the channel to erode upwards. Because of this the channels are most commonly found near the glacier outlet where the pressure is less

Question 28

What is the balance between ice overburden pressure and hydraulic potential at rothlisberger channels?

Answer 28

ice overburden < hydraulic potential

Question 29

What will happen to rothlisberger channels usually at the end of summer and why?

Answer 29

They will be forced to close up because of the diminishing supply of water to the base of the glacier that will reduce the hydraulic potential of the water and so the overburden pressure will exceed it. This happens at the end of summer because ablation starts to tail off at the end of this season

Question 30

What happens at the tunnel boundary of the rothlisberger channels?

Answer 30

Overburden pressure = hydraulic potential and so any changes to either will affect the shape of the tunnel

Question 31

What are nye channels and how are they formed?

Answer 31

These are channels created in the sediment/bedrock below the ice because the ice overburden pressure buries the channel to force erosion happening downwards

Question 32

When is a nye channel more likely to be preserved?

Answer 32

if the channel is eroded in to underlying bedrock as opposed to sediments because the latter are more easily reworked over time

Question 33

What are water films and when are they caused?

Answer 33

Thin layers of water at the base of usually a temperature ice body which is prone to basal melting which provided a supply of water to the base of the glacier

Question 34

Why is it hard to observe water films?

Answer 34

because they exist at the base of a glacier which is hard to access

Question 35

What is a water film limited in its ability to do?

Answer 35

transport material because it is such a small amount of water

Question 36

What is a water film fundamental for?

Answer 36

Regelation which is effectively what permits glacier basal sliding

Question 37

What is a linked cavity system and how do they occur?

Answer 37

water-filled cavities at the bed of a glacier where basal pressure exceeds the local ice pressure. The cavities allow for greater basal motion which creates more cavities thereby forming a positive feedback

Question 38

What is groundwater flow?

Answer 38

water flowing through sediments below the glacier, only sediments.

Question 39

What determines the amount of water flow through these sediments and how?

Answer 39

Darcy's Law - this calculates the likely discharge of water through a material

Question 40

What is likely to be the groundwater flow through poorly sorted sediments and well sorted?

Answer 40

Poorly sorted sediments are impermeable so groundwater flow will be minimal but for well sorted sediments this is reversed.