Natural hazards in glaciated landscapes

Glaciated landscapes face various natural hazards.

Avalanches and their causes

Avalanches are mass movements of snow, ice, and rocks down a slope, and they are becoming more common in glacial regions due to changing weather patterns.

Key types of avalanches:

• Powder avalanches - These involve snow particles suspended in the air as they flow downslope, often occurring without much moisture.
• Slab avalanches - Large sections of snow and ice break away due to a weak layer at the base, often caused by basal meltwater refreezing into a less cohesive structure.
• Wet avalanches - These contain significant meltwater, making the snow slushy and heavy as it descends.
• Dry avalanches - These require little meltwater and rely on gravity and snow instability for movement.

Climate change contributes by causing heavier snowfall events, which add fresh, unstable snow to a glacier's zone of accumulation. This fresh snow is more prone to movement because it hasn't compacted like older layers.

Impacts of avalanches

• Human risks - More people are at risk due to increased recreational use of upland areas. For example, between 2010 and 2019, 256 people died from avalanches in the USA, compared to 53 between 1960 and 1969.
• Landscape changes - They can transport glacial deposits far from their original positions and create new erosional features.
• Formation of lahars - Some avalanches, especially those triggered by volcanic eruptions, mix with loose soil to form lahars (mudflows).

Glacial outburst floods

A glacial outburst flood, also known as a jökulhlaup, is a sudden release of meltwater from beneath an ice mass.

Causes of glacial outburst floods:

• Geothermal activity - Heat from the Earth's crust causes basal heating, melting ice and releasing englacial meltwater.
• Moraine dam failure - The sudden breakup of terminal moraine walls that hold back meltwater lakes.

These floods threaten lives and modify landscapes by relocating deposits and creating new erosional features.

Human activities threatening glaciated landscapes

Tourism in polar and glacial regions has grown significantly.

Tourism impacts

• Marine pollution - Larger cruise ships visiting polar areas increase the risk of marine pollution in sensitive marine environments.
• Noise and habitat disruption - Tourist noise stresses wildlife, like penguin colonies in Antarctica, reducing breeding success and overall biodiversity in areas already low in species variety.
• Seasonal pressures - In places like the Alps, winter sports (skiing, snowboarding) and summer activities (mountain biking, climbing, bird watching) attract crowds, leading to habitat loss.

Construction impacts

• Dams and reservoirs - These block migratory routes for fish, preventing access to spawning grounds, which reduces fish populations and affects food chains.
• Hydroelectric power plants (HEP) - They alter river regimes, changing discharge, sediment levels, and deposition sites, harming aquatic life.

Fish like salmon travel long distances to spawn, so disruptions have a widespread impact.

Urbanisation impacts

• Settlement growth - In places like Alaska's North Slope near Prudhoe Bay, settlements for workers extracting fossil fuels or minerals expand with added shops and services.
• Urban heat islands - These localised warm areas raise temperatures, causing permafrost to thaw, leading to subsidence of buildings and disruption of tundra habitats that depend on the permafrost.

Degradation from human actions in glaciated landscapes

Litter and pollution

• Increased visitors lead to more litter, which pollutes water sources and harms wildlife by damaging habitats.
• In cold climates, decomposition is slow, prolonging the impact on animals and humans reliant on clean water.

Soil erosion and landslides

• Trampling effects - Hikers straying from paths compact soil, reducing infiltration, which lowers vegetation regrowth and raises flood risks.
• Landslide risks - Compacted, rootless soil becomes unstable, especially after heavy rain, as meltwater washes away exposed soil.
• Management efforts - Signage in areas like the Himalayas and Lake District aims to keep visitors on paths to protect ecologically sensitive zones.

Introduction of alien species

Visitors unintentionally bring non-native species, such as seeds on boots or mussels on ship hulls in polar regions.

Deforestation

Trees are cleared for access roads, car parks, resorts, and ski runs, spoiling landscapes and destabilising soil. This increases saturated overland flow, raising flood risks and landslide potential.

In the Alps, tree removal for expanded resorts has made slopes more prone to avalanches and landslides, with climate change adding variability to meltwater patterns.

Climate change impacts on glacial mass balance and hydrology

Negative mass balance and retreat

• Most glaciers worldwide have a negative mass balance, leading to retreat.
• Melting in Greenland and Antarctica contributes to rising sea levels, threatening low-lying coastal areas with flooding.

Permafrost melting in regions like Alaska creates a positive feedback loop:

1. Melting releases trapped carbon as methane and carbon dioxide.
2. These gases enhance the greenhouse effect.
3. Higher temperatures cause further melting, perpetuating the cycle.

Disruptions to the hydrological cycle

• Short-term flooding - Sudden meltwater surges increase river discharge, saturating soils and raising flood risks, especially if the water table is near the surface.
• Long-term water shortages - As glaciers retreat, meltwater supplies diminish, affecting:
  • Hydroelectric power viability due to insufficient water.
  • Aquatic life, particularly fish, from reduced flows.
  • Water quality, as pollution concentrates in slower rivers.
  • Sediment transport, with deposition reducing channel size and increasing flood risks.

Specific threats to Himalayan glaciers

Increased mountaineering and local changes

• Advances in equipment and media attention have boosted Everest climbs, with over 800 summits in 2018 compared to about 1,300 between 1953 and 2000.
• This contributes to a rising snowline as local microclimates warm, with around 75% of Himalayan glaciers retreating.

Impacts on water and infrastructure

• Over 600 dams in the Himalayas supply power to countries like India, Bhutan, Nepal, and Pakistan, but reduced meltwater may cause reservoirs to dry up and fill with sediment, rendering them inefficient.
• Meltwater supports over 1 billion people for drinking, irrigation, and energy; rapid ablation leads to flooding and wasted resources, rather than steady river flows.

Deforestation effects

Deforestation in Nepal exposes soil.

This leads to:

• Increased sedimentation in rivers, pressuring agriculture (employing 64% of the workforce) by reducing land productivity.
• Higher landslide risks on slopes where many people live.