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
