GLACIERS AND ENVIRONMENTAL CHANGE PART I

Modelling of ice sheet, ice mass and mass balance studies advance understanding of global ice sheet fluctuations in the past

Effect of modern glaciers in 2 levels

• They impact upon humans and habitats in their nearby surroundings, meltwater outbursts and rapid ice advances resulting in the loss of pasturelands, property and human fatalities
• Large scale impact on global climate
  

Techniques of studying glaciers

• Satellite images improved the accuracy or measured ice movement and mass balance
• Ice-core studies
• Computer generated ice-sheet models
• Spatial and temporal development of Pre-Pleistocene and Pleistocene ice-sheets
  

International organizations

World Glacier monitoring service (WGMS) of International Commission on Snow and Ice (ICSI/IAHS0 – Part of Global Environmental Monitoring System ( GPMS)

Two Types of Data –

1. Summary information
2. Extensive information
   

Summary information

Specific balance
Cumulative specific balance
Accumulation Area Ratio (AAR)
Equilibrium Line Altitude (ELA)

Extensive Information
Balance maps
Balance/altitude diagrams
Relationship between accumulation area ratios
Equilibrium line altitude, balance
Explanatory text and Diagram

Study of Past Glacier Fluctuations

Sequence of glacials and interglacials driven by earth’s orbital parameters

External forcing mechanism
Responses and chain reactions in the external elements (atmosphere, ocean, the hydrological cycle, vegetation cover, glaciers and ice sheets)

Glacial surges not related to climate

Hysithermal – early to middle Holocene, a time of glacial retreat and warmer climate

Neoglaciation – rebirth and readvance of most alpine glaciers in Late Holocene

Little Ice age (last 4-5 centuries), repeated glacier fluctuation – ELA lowered by 100
– 200m

Theories of Climate and Glacier Variation

Milankovitch theory of climatic Variation

Based on the assumption that earth’s orbit and axis cause surface
temperature changes on the Earth

• Eccentricity of Orbit – orbit shape changes from circuler to elliptical in cycle of 100,000 years due to influence of other planets
• Obliquity of the elliptic – tilt of the earth’s axis varies from 21-39 to 24-36 in a period of 42,000 years
• Precession of the equinoxes or precession of the solstices – the seasons when earth is nearest to the sun varies with cycles of 23,000 and 19,000 years
  

Glacier monitoring

Specific Balance, cumulative specific balance, accumulation area ratio (AAR), equilibrium line method (ELA) and Length Changes

Remote Sensing Techniques in studying glaciers

1. Measurement of the ice thickness by radio-echo sounding from surface and airbourne platforms
2. Changes in surface elevation overtime with aerial photogrammetric methods and by geodetic airborne and space borne radar and laser altimetry
3. Declination of surface expression and glacier faces with satellite sensors.
   

Supraficial Ice Morphology

Crevasse are formed where ice is pulled apart by tensile stresses that exceeds strength of ice – reflection of stress orientation of glacier

• Chevron Crevasses are liner feature oriented obliquely up valley from a glacier margin towards the centre of the glacier – 45 to valley walls
• Splaying or marginal crevasses are formed due to compressive flow – curved parallel to flow direction
• Traverse Crevasses – in Valley Glacier as a result of extending Flow near centre, the main tensile stress is parallel to the glacier flow. At right angles to the Centre-line
• Longitudinal crevasses – lateral stress increases as a result of widening of valley glaciers
• Randkluft – fissure separating the glacier from the rock wall, because movement away from rockwall and ablation adjacent to warm rock surface
• Bergschrunds – deep traverse crevasses near the heads of valleys and cirque glaciers.
• Seracs – icefalls are steep parts of a glacier where the flow is rapid and intermittent avalanches are triggered by collapse of ice blocks. Piling up cones of broken ice at the base of icefall
• Ogives – irregular bands or waves on surface of valley glaciers below icefalls. Convex down glacier due to higher speed at the centre dark bands in summer due to windblown dust and superficial material, excess snow- light in winter
• Foliation – Layering reflect annual cycles of snow accumulation. Foliation formed in deep ice in the accumulation area and is formed in the englacial and supraglacial ice. Parallel movement of layers
1. Traverse – crevasses traces downglacier from traverse crevasses and icefalls
2. Longitudinal – parallel to glacier flow and formed by the rotation of ice and crevasses layers

SOURCE

GLACIERS AND ENVIRONMENTAL CHANGE

ATLE NESJE AND SVEIN OLAF DAHL