6.3: Glacier hydrology - the role of meltwater Flashcards
Name the 2 main sources of meltwater from glaciers
- surface melting
- basal melting
Surface melting contributes most of the supply of glacial meltwater and peaks in late …?: it is the only source of meltwater for …? basal glaciers. supraglacial surface …? form running along the top of the ice, especially in the …? zone. They are often fast flowing and may plunge down into the glacier becoming …?
- summer
- cold
- streams
- ablation
- englacial
Basal melting occurs if temperatures of the ice at the base of a glacier is at …? melting point (in a warm-based glacier). The basal meltwater flows under …? pressure beneath the glacier and can excavate subglacial …? cutting through the bedrock. The meltwater streams eventually …? from glacial tunnels at the glacier snout via portals (…?)
- Pressure
- Hydrostatic
- tunnels
- emerge
- caves
Name 2 reasons why fluvo-glacial streams operate differently than other streams?
High pressure and velocity of flow
Fluvo-glacial steams have high pressure and …? of flow. This causes the erosion of underlying bedrock by abrasion, cavitation and …? means beneath the ice, and can also lead to intense …? by meltwater streams as they exit the glacier …?. The ablation rates are very …? during de-glaciation, and many if the meltwater streams have very high …? leading to powerful erosion.
- velocity
- chemical
- erosion
- snout
- high
- Discharges
When meltwater deposits material subglacial, englacial and supraglacial, the material is referred to as…
an ice-contact fluvio-glacial deposit
Name 3 key characteristics of fluvo-glacial deposits
- generally smaller than glacial till as meltwater streams; although having high discharge, they still have less energy than large valley glaciers so they generally
- generally smoother and rounder through water contact and attrition
- sorted horizontally, especially in the case of outwash deposition, with the largest material found up-valley or nearer the glacier snout, and progressively finer material down-valley, due to the sequential nature of deposition mechanisms
- stratified vertically with distinctive layers that reflect either seasonal or annual sediment accumulation
what is the difference between fluvo-glaivally deposited material and glacial till?
Glacial till is angular, poorly sorted and non-stratified whereas fluvo-glacial deposits tend to be rounder, smoother and sorted
What is the difference between fluvio-glacial deposits and outwash deposits?
Outwash deposits experience more attrition, causing clasts to become more rounded and the material is better sorted horizontally
Name the 3 zones of outwash deposits
- Proximal zone
- Medial zone
- Distal zone
What zone of outwash plain is described?
Immediately in front of the glacier, close to the snout. Meltwater has greatest power here so the outwash deposit contains a large particle size. Outwash may be interbedded with layers of till as some glacial deposition may occur. Outwash may occur in alluvial fan forms.
Proximal zone
What zone of outwash plain is described?
Further from ice margin, meltwater streams tend to anastomose and form braided channels because of high daily and seasonal variability of meltwater discharge. Particle size is less coarse than in the proximal zone and clasts are more rounded.
Medial zone
What zone of outwash plain is described?
Furthest from ice margin. Drainage pattern resembles normal drainage system, with meanders on a broad flood plain. Outwash is well sorted and characterised by smaller and even more rounded particles.
Distal zone
Name this fluvo-glacial depositional feature by its description
Long, sinuous ridges on the valley floor
Eskers
Name this fluvo-glacial depositional feature by its description
Small mounds on the valley floor
Delta Kames
Name this fluvo-glacial depositional feature by its description
Ridges of material running along the edge of the valley floor
Kame Terraces
Name this fluvo-glacial depositional feature by its description
Layers of sediment found at the bottom of lakes
Varves
Name this fluvo-glacial depositional feature by its description
A flat expanse of sediment in the proglacial area
Outwash (sandur)
Name this fluvo-glacial depositional feature by its description
Small circular lakes in outwash plains
Kettle holes
Name this fluvo-glacial depositional feature by its formation
Material is deposited in subglacial tunnels as the supply of meltwater decreases at the end of the glacial period. As a glacier retreats it deposits this tunnelled material on the valley floor
Eskers
Name this fluvo-glacial depositional feature by its formation
Englacial streams emerging at the snout of the glacier fall to the valley floor, lose energy and deposit their load, or supraglacial streams deposit material on entering ice marginal lakes.
Delta Kames
Name this fluvo-glacial depositional feature by its formation
Supraglacial streams on the edge of the glacier pick up and carry lateral moraine, which is then deposited on the valley floor as the glacier retreats.
Kame Terraces
Name this fluvo-glacial depositional feature by its formation
Sediment carried by meltwater streams is deposited on entering a lake as energy is lost. In summer, when large amounts of meltwater are available, the sediment is coarse and plentiful, leading to a wide band of sediment of relatively large material. In winter, with little meltwater present, sediment is limited in amount and size, so the bands are thin and fine.
Varves
Name this fluvo-glacial depositional feature by its formation
As meltwater streams gradually lose energy on entering lowland areas, they deposit their material. The largest material is deposited nearest the snout and the finest further away.
Outwash (sandur)
Name this fluvo-glacial depositional feature by its formation
During ice retreat blocks of dead ice become detached. Sediment builds up around them and, when they eventually melt, a small hollow is formed in which water accumulates to form a lake.
Kettle Holes
Name the Fluvio-glacial landform from it’s description
They are formed along the front of glaciers and ice sheets where meltwater from the glacier becomes impounded within a depression blocked by glacier ice and bunded by high ground. They are ephemeral (temporary) features; depending on the rapidity of deglaciation the pro-glaciation lake can empty completely or stabilise at a lower level if the ice margin doesn’t completely disappear
Proglacial Lake (also known as ice-margin lakes)
