Glacial environments

Sweden after the last ice agearound 10,000 years ago

Above sea-level

Under sea-level

A glacier is a system

• Inputs: accumulation of snow and debris• Storage: ice and debris• Outputs: melt, vapour and sediment

Glacial systems

• When accumulation is greater a glacier advances

• When ablation (loss) is greater a glacier retreats

• If accumulation = ablation a glacier is steady

Glaciers move by inner deformation

Alpine glaciersthat ablate on land

• Ablation leaves lakes and/or deposition

Coastal glaciersthat ablate into the ocean

• Ablation causes calving = icebergs

Glacial erosion

• Glaciers carry abrasive material• Rate of erosion = geology + velocity + weight +

load• Crushing (weight)• Plucking (freezing)• Abrasion (by debris)

Landforms and erosive featuresEvidence of glaciation

Roche moutonnée (sheepbacks)

• Tear-shaped rock formations shaped by ice• Blunt, broken end away from direction of ice

flow, caused by plucking

Roche moutonnée (sheepbacks)

Ice flow

Stoss sideLee side

Roche moutonnée - Farsta

Visible on roche-moutonnées

• Small details reveal ice movement

Striations (scratches)

Local striations in

Farsta

Glacial groove? at Orhem – near Flaten (p-form)

Chatter marks

Direction of movement

Hälsingland

Large scale glacial forms – features of erosion

Cirques/corries

• A short alpine glacier that forms in a hollow depression called a cirque (also known as a corrie)

Cirque formation

Arêtes and pyramidal peaks

• An arête is a sharp ridge formed when two cirques cut back

• A pyramidal peak is formed by 3 or more cirques cutting back

A glacial u-shaped valley (trough)

• Misfit river – seems too small

Fjord (drowned glacial valley)with a hanging valley

• A hanging valley is a cut-off tributary glacier

Ribbon lakes

• Filled glacial valleys (rock basins)

Glacial valley with rock basin forming a ribbon lake

Glacial deposition

• Post-glacial landscapes contain many features “left behind” after glaciation

• Formed of till and moraines– Unsorted and unstratified “soils” composed of

different particle sizes – boulders, pebbles, clay

Deposition: erratics

• Erratics are large “foreign” boulders transported by glaciers

Erratics – transported bouldersOrhem – near Flaten

Coastal erratic

Hälsingland

Deposition: drumlins

• Streamlined, teardrop shaped hills & hillocks• Formed of till left by glaciation• Blunt end facing opposite ice flow• Often found in “shoals”

Drumlins

Ice flow

Deposition: moraines

• Deposits of material left by retreating glaciers• Consist of unsorted till and erratics• Terminal/end moraine– Deposited by retreating glacier at its point of

farthest reach– May create a dam holding a proglacial lake

• Lateral moraines– Deposited along the sides of retreating glaciers

Moraines

Lateral moraine

Terminal moraine

Eskers – gravel ridges • Meltwater forms a tunnel under a

glacial ice sheet• Tunnel fills with rocks, sand and

gravel

• After retreat of the ice, material collected in the tunnel is left to form a ridge

Near SiljanAfter glacial retreat this sharp-ridged eskerWould have been above sea level

Eskers – economic benefits

• Traditionally used as roads

• Used for natural water filtration

• Mined for materials – sand, gravel and stones for construction

Living in glaciated regions

Description of landscape:• Most sedimentary rocks have

been removed• Granites and gneiss rocks are

less porous so the landscape tends to hold a lot of water

• Makes the ground swampy, many lakes and soils are in general thinner

• Glacial soils (clay) collects in valleys

Living in glaciated regions

• Soils generally less fertile (soil is a resource)

• There is less agricultural land – too much rock

• Ground needs draining • High latitudes means

shorter growing season• Wheat and grasses,

forestry, livestock are more common

Making new land

• The agricultural land shortage in Sweden during the 1800s was so acute that during the period 1880 – 1950 over 20,000 lakes were sunk to create new farmland

Alpine regions

• Glaciation produces steep mountains with deep valleys

• Difficult communications (roads etc)

• Limited land for building• Snow for much of the year• High altitiudes lowers

biodiversity and growing season

• Greatest risks are from landslides (rock, mud, soil) and avalanches (snow)

Alpine regions

• Advantage is the availability of hydropower

• Modern communities turning to winter sports for as an economic resource