Geog - glaciated landscapes

facts about ice coverage

10% now, 30% at last glacial max

current ice stored in Antarctica and Greenland 96%

Examples of unconstrained vs constrained glaciers

unconstrained - ice caps, ice sheets, ½ piedmont

constrained - valley, cirque, ½ piedmont

Formation of glacial ice including facts about density

1. Fresh snow - low density and open structure - 0.05 g/cm3

2. snow that survives 1 summer is called firn - 0.4 g/cm3

3. glacial ice between that takes between 30-1000 years to form and is not encountered until 100m deep - 0.83-0.91 g/cm3

Snow is 90% air whilst ice is 20-30% air

warm vs cold based glaciers

warm - high altitude low latitude, steep relief, basal temperature is at or above PMP - rapid movement of 20-200m per year

cold based - low altitude high latitude, basal temperatures below PMP, may only move a few metres a year max

ways a glacier can move

1. internal deformation (creep) - slippage within and between ice crystals, greatest at the base where pressure is at a max

2. Basal sliding - basal slip from meltwater

• enhanced basal creep - plastic deformation - no melting, just changing shape around an obstacle

• regelation flow - melting and refreezing around an object

Examples of inputs, throughputs and outputs for glaciers as a system

inputs - solar energy, debris from rockfall, snow, precipitation, kinetic energy (wind), GPE (from the altitude)

throughputs - snow, ice, meltwater, GPE to kinetic energy as moves downslope

outputs - thermal energy, meltwater, vapour (evaporation and sublimation), calving and debris

What is the mass balance of a glacier

accumulation - ablation over a year

Describe the negative feedback loop of a glacier

• glacial system in dynamic equilibrium

• air temperature increases causing more ablation and meltwater as it reaches PMP on base and top

• ablation > accumulation so negative mass balance

• glacier retreats up the valley

• colder temperatures higher up

• rate of ablation drops

• glacial system in dynamic equilibrium

Describe the positive feedback loop of a glacier

• system in equilibrium

• meltwater means increased crevasses

• more heat absorbed due to increased albedo from exposed rock

• increased ablation and mass loss

• meltwater percolates through increasing speed of flow

• more crevasses - more bare rock exposed

• decreased albedo

Factors affecting glaciated landscapes

climate - summer more precipitation but does not fall as snow so less accumulation, affects the velocity of the glacier

geology: lithology - chemical and physical composition e.g. clay and limestone (soluble) weak, basal strong, structure - joints, beddings and PERMEABILITY

relief and aspect - if aspect is towards sun then the snow is less likely to survive summer, steeper relief leads to more crevasses

Altitude and latitude - cold vs warm based, also affects concentration of insolation (ice caps likely to be found at lower altitude and higher latitude)

Describe the process of nivation

snow falls into depressions or hollows

it is compacted into névé and then firn - weathering can erode rocks under the snow

over time this creates a nivation hollow which can form a corrie/cirque

Formation of a roche moutonee

Igneous intrusion in the ground - glacier cannot fully erode like surrounding bedrock

PMP reached on stoss side so meltwater produces

subglacial debris is scraped across the stop causing some abrasion

temperature drops on Lee side causing meltwater to refreeze and leading to plucking - jagged lee side

formation of striations

glacial debris abrading surrounding bedrock leaving scratches parallel to ice flow

Formation of cirque/corrie/cwm

snowpack builds up on the shade side of a mountain creating a nivation hollow

glacial ice develops and begins to rotate which leaves a gap at the back - Bergschrund

plucking steepens this back wall leading to pressure release and water in the Bergschrund

Arretes and pyrimidal peaks

arrete is two corries back to back, a pyramidal peak is more than 2 creating a steep point

Morraine formation

terminal morraine - position of maximum advancement and deposition at the snout

recessional morraine - ridges run transversely and parallel to each other and the terminal morraine - show a temporary standstill

lateral morraine - runs along edge of glacial valley from material fallen onto glacier from erosion of valley sides

Formation of Erratics

individual pieces of rock composed of a different geology that is not from the area they have been deposited in - highlights transportation and deposition from the glacier

Formation of till sheets

large unsorted expanses of glacial till that has been deposited in the retreat of an ice sheet - composition is determined by the where the ice sheet has flowed

formation of drumlins

1. rock cored - large obstacle in centre around which sediment builds up over time

2. subglacial sediment deformation - saturated sediment is moulded by the glacier above it due to differences in ice flow speed

Snowdonia case study

Nant Ffrancon valley

most recent glacial period (Devensian) from 110,000 - 10,000 years ago with a maximum at 18,000 years ago

Welsh ice cap that covered Nant Ffrancon valley was up to 1km thick

Corrie - Cwm Idwal, not circular - 1.5km long but only 1km wide, also very deep (375m)

Tarn (corrie lake) - Llyn Idwal

Misfit stream - Afon Ogwen

Ribbon Lake - Llyn Ogwen

Arete - y Gribin

truncated spurs - Gribin Ridge

Laurentide Ice Sheet case study

In Minnesota - the land of 10,000 lakes

4km deep ice sheet that sat over Northern USA and Canada

during the Wisconsin glaciation (110,000 -10,000 years ago with a max at 18,000)

advanced and retreated due to temp changes of up to 5 degrees

THE ARROWHEAD REGION - layers of tectonically tilted rock alternating between weaker shales and more resistant volcanic basalt

• Lake Vermillion is 23m deep and made of eroded shales

Highest point in the state is only 701m - ellipsoidal basin

many of the lakes are kettle lakes

Lake Agassiz - huge pro-glacial lake 440,000km2

Lobes in Minnesota (direction and geology of deposited material)

Wadena Lobe - northwest, grey from limestone in Winnipeg leading to the Alexandria morraine

Des Moines - northwest but coming in at south of state, grey-brown

Rainy lobe - northeast, brown and sandy

Superior lobe - east, red in colour with rocks from lake superior

History behind current interglacial

Holecene period - began 11,700 years ago leading to a retreat of glaciers and thus glacio-fluvial landforms due to exessive amounts of meltwater

Characteristics of glaciofluvial landforms

Stratified - distinctive layers

sorted - biggest to smaller

imbricated - long axis aligned in one direction

rounded - attrition

graded

formation of a kame

sediment being glaciofluvally transported descends from the supre-glacial into the crevasses and other depressionss

the water loses energy and eventually stops moving

when glacial retreats, it reveals these mounds of deposited sediment on the valley floor

often in a conical shape

delta kame - streams flow out of the terminus of a glacier and into a lake where sediment is deposited

formation of an esker

formed by deposition from a meltwater stream that was flowing in a tunnel in a glacier

How do these landforms change over time

warmer temperature - rivers flow further and have more energy

vegetation - less sediment in the rivers as held together by roots, but adversely more biological weathering

mass movement - mounds of sediment that will therefore not be stratified or sorted

Periglacial landscape defining characteristic

permafrost

• sporadic - thinner, fragmented layers at borders of discontinuous zones

• discontinuous - patched of unfrozen and frozen where temperature lies between -5 and -1 degrees

• continuous - fully permafrost (>500m deep)

Describe periglacial process of formation of ice lenses and ground ice

An ice lens forms from frozen water in the ground

liquid water moves towards this ice through capillary action

ground will push upwards as the lens starts to grow

describe process of frost heave

Upwards movement of rocks and stones through soil from frost push and frost pull

• rock is frozen to above sediment and thus gets pulled upwards at the formation of an ice lens leaving a gap below

• smaller stones and ice fill in this gap meaning the rock is then pushed upwards

• these two processes continue until the rock is at the surface

ALSO FREEZE-THAW WEATHERING

Periglacial landforms

rocks on surface due to frost heave - sometime patterned ground, can create stone circles as heavy sediment rolls down ice lens hill

pingos

• OPEN - found in discontinuous areas of permafrost where groundwater is more readily available, enlarged from below the ground

• CLOSED - found in areas of continuous (downwards growth of permafrost). There is a lake freezes from the top and the sides first as permafrost grows, meaning it traps the water, become pressurised when it begins to freeze, leading to the expansion of the ground

CS1: Prudhoe Bay - Alaska

permafrost lies under 80% of the ground

250 miles north of the Arctic circle

pipeline transports the oil from Alaska to mainland America or to ice-free port of Valdez

Issues in Prudhoe Bay

Urban heat island - Barrow 2.2 degrees warmer than surrounding area and population has grown from 300 in 1900 to 4600 in 2000

Increases of air temperature - burning of excess gases (flaring)

heat from individual buildings

removal of vegetation for housing - permafrost is less insulated

all this leads to: permafrost thaw and degradation, thawing of ice lenses, Thermokarst landscape (hummocky ground, surface depressions, water logged soil, Alses (pools as ground ice melts)

SOLIFLUCTION LOBES - saturated sediment moving downslope under gravity

ways to manage the issues in PB

Gravel pads - reduce thermal energy BUT the sediment is extracted from streams or river beds to affects downstream gravel transport and changes the erosional/depositional balance

CS2: Grand Dixence Dam

south-west Switzerland at the head of Val Des Dix

highest gravity dam in the world (285m high) with meltwater from 35 glaciers

400million m3 of water

HEP contributed over 60% to Swiss energy

less social impact as few humans so flooding was not that bad

Sediment issues for Grand Dixence dam

sediment build up occurs at 20-40cm a year on the upstream side

Concentration above the dam is 300mg/l and below is 20-50mg/l

sediment input to lake Geneva has almost halved