2.3.1
Mass Balance
Inputs and Outputs of Glacial Systems
Inputs and Outputs of Glacial Systems
Glaciers operate as a system with inputs (accumulation) and outputs (ablation) and both influence the mass balance of a glacier.
Inputs (accumulation)
Inputs (accumulation)
- Direct snowfall and other forms of precipitation.
- Meltwater from melting snow and ice that re-freezes.
- Rock fragments that have fallen on to the glacier or been eroded by it.
- Avalanches of snow and/or rock, and wind-blown deposits.
- Solar energy. But, snow and ice have a high albedo meaning much radiation is reflected (up to 90%).
Outputs (ablation)
Outputs (ablation)
- Meltwater during the spring and summer months.
- Sublimation and evaporation can take place all year round, but mostly occur in summer.
- Meltwater streams also transport eroded material. They are often cloudy as they contain rock flour.
- Calving into lakes and the sea.
- Solar energy reflected in the albedo effect.
Mass Balance
Mass Balance
The mass balance of a glacier is influenced by inputs and outputs of glacial systems and can change over time, both long-term and short-term.
Budget
Budget
- The mass balance (budget) is the relationship between accumulation and ablation.
- If accumulation is greater than ablation, the glacier gains mass and the glacier snout advances.
- If ablation is greater than accumulation, the glacier loses mass and the glacier snout retreats.
- If accumulation is equal to ablation, the snout of the glacier remains in the same place - it is stationary.
Equilibrium lines
Equilibrium lines
- An equilibrium line can be shown on a glacier where at any one time the amount of accumulation equals that of ablation.
- This is also known as the firn line.
Spatial variations
Spatial variations
- There are spatial variations in a glacial budget.
- Most of the accumulation occurs at the upper end of a glacier because at higher altitudes it is much colder so this exceeds losses due to ablation.
- There is, therefore, net accumulation and this part of a glacier can be called the accumulation area.
- At the lower end of a glacier, the reverse is the case and ablation at warmer, lower altitudes exceeds accumulation.
- So, there is net ablation and this part of a glacier is called the ablation area.
Temporal Variations and Feedback Mechanisms
Temporal Variations and Feedback Mechanisms
The mass balance of a glacier can change over time. Feedback mechanisms also play a significant role.
Temporal variations
Temporal variations
- There are temporal variations in a glacial budget.
- During winter months, there is a net accumulation in the glacial budget and so the glacier expands (positive balance).
- During summer months, there is a net ablation in the glacial budget and so the glacier reduces in size (negative balance).
Feedback mechanisms
Feedback mechanisms
- Positive feedback - a small increase in snowfall caused by a lowering of temperature would increase the albedo of the ice surface, contributing to further cooling and more accumulation.
- Negative feedback - higher temperatures would increase evaporation and therefore precipitation (snowfall) so more snow accumulation balances the losses from ablation at higher temperatures.
1Tectonic Processes & Hazards
1.1Tectonic Processes & Hazards
1.2Natural Disasters
1.3Natural Disaster Case Studies
1.4Trends & Patterns
2Option 2A: Glaciated Landscapes & Change
2.1Glaciated Landscapes Over Time
2.2Periglacial Landscapes
2.3Glacial Processes
2.4Glacial Landforms
3Option 2B: Coastal Landscapes & Change
3.1Coastal Landscapes
3.2Coastal Erosion & Deposition
3.3Coastal Risks
4Globalisation
4.1Globalisation
4.2Negatives of Globalisation
4.3Global Shift
4.5Culture
4.6Measuring Development
5Option 4A: Regenerating Places
5.1Types of Economies
5.2Function of Places
5.3Regeneration
5.4Regeneration Case Studies
6Option 4B: Diverse Places
6.1Population Structure
6.2Past & Present Connections
6.3Urban & Rural Spaces
6.4Diversity
6.5Urban & Rural Case Studies
6.6Case Study - Tower Hamlets
6.7Case Study - Sturton-le-Steeple
7The Water Cycle & Water Insecurity (A2 only)
7.1Hydrological Processes Global to Local
7.2Influences on the Water Cycle
7.3Water Insecurity
8The Carbon Cycle & Energy Security (A2 only)
8.1The Carbon Cycle
8.2Energy Consumption
8.3Alternative Energy
8.4Growing Demand for Resources
9Superpowers (A2 only)
9.1Superpowers
9.2Hard & Soft Power
9.2.1Hard & Soft Power
9.2.2Emerging Powers - China Rivalry
9.2.3Emerging Powers - Chinese Sources of Power
9.2.4Emerging Powers - Brazil
9.2.5Emerging Powers - Russia
9.2.6Emerging Powers - India
9.2.7Theories of Development
9.2.8Power Case Studies: Chinese One Belt One Road
9.2.9Power Case Studies: Pakistan Nuclear Arms
9.2.10Power Case Studies: OPEC
9.3IGOs, TNCs & Alliances
10Option 8A: Health & Human Rights (A2 only)
10.1Human Development
10.2Role of Governments & IGOs
10.3Human Rights
10.4Interventions
11Option 8B: Migration & Identity (A2 only)
11.1Globalisation & Migration
11.2Consequences of Migration
11.3Nation States
11.4Responses to Global Migration
Jump to other topics
1Tectonic Processes & Hazards
1.1Tectonic Processes & Hazards
1.2Natural Disasters
1.3Natural Disaster Case Studies
1.4Trends & Patterns
2Option 2A: Glaciated Landscapes & Change
2.1Glaciated Landscapes Over Time
2.2Periglacial Landscapes
2.3Glacial Processes
2.4Glacial Landforms
3Option 2B: Coastal Landscapes & Change
3.1Coastal Landscapes
3.2Coastal Erosion & Deposition
3.3Coastal Risks
4Globalisation
4.1Globalisation
4.2Negatives of Globalisation
4.3Global Shift
4.5Culture
4.6Measuring Development
5Option 4A: Regenerating Places
5.1Types of Economies
5.2Function of Places
5.3Regeneration
5.4Regeneration Case Studies
6Option 4B: Diverse Places
6.1Population Structure
6.2Past & Present Connections
6.3Urban & Rural Spaces
6.4Diversity
6.5Urban & Rural Case Studies
6.6Case Study - Tower Hamlets
6.7Case Study - Sturton-le-Steeple
7The Water Cycle & Water Insecurity (A2 only)
7.1Hydrological Processes Global to Local
7.2Influences on the Water Cycle
7.3Water Insecurity
8The Carbon Cycle & Energy Security (A2 only)
8.1The Carbon Cycle
8.2Energy Consumption
8.3Alternative Energy
8.4Growing Demand for Resources
9Superpowers (A2 only)
9.1Superpowers
9.2Hard & Soft Power
9.2.1Hard & Soft Power
9.2.2Emerging Powers - China Rivalry
9.2.3Emerging Powers - Chinese Sources of Power
9.2.4Emerging Powers - Brazil
9.2.5Emerging Powers - Russia
9.2.6Emerging Powers - India
9.2.7Theories of Development
9.2.8Power Case Studies: Chinese One Belt One Road
9.2.9Power Case Studies: Pakistan Nuclear Arms
9.2.10Power Case Studies: OPEC
9.3IGOs, TNCs & Alliances
10Option 8A: Health & Human Rights (A2 only)
10.1Human Development
10.2Role of Governments & IGOs
10.3Human Rights
10.4Interventions
11Option 8B: Migration & Identity (A2 only)
11.1Globalisation & Migration
11.2Consequences of Migration
11.3Nation States
11.4Responses to Global Migration
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