This key knowledge requires you to understand the physical properties of glaciers, ice sheets and forests — the two land cover types at the centre of Unit 3 Area of Study 1. These characteristics explain why each is vulnerable to change and why each matters ecologically.
A glacier is a persistent body of dense ice that forms where annual snowfall exceeds melting over many years. Key characteristics:
Formation and structure
- Snow accumulates in a zone of accumulation (high altitude/latitude), where it compacts into firn and eventually glacial ice (~830 kg/m³, compared to ~917 kg/m³ for pure ice)
- Ice flows downslope under its own weight — a key distinction from static snow fields
- The equilibrium line altitude (ELA) separates accumulation (above) from ablation (below); a rising ELA indicates glacier retreat
Types of glaciers
- Alpine/valley glaciers: confined to mountain valleys; found in Alps, Himalayas, Andes, Southern Alps (NZ)
- Ice caps: dome-shaped, covering highland areas; Iceland, Patagonia
- Outlet glaciers: tongues of ice sheet draining to the sea; Jakobshavn Glacier (Greenland)
Ecological and hydrological role
- Store approximately 69% of Earth’s fresh water
- Act as “water towers” — slow-release reservoirs for rivers fed by meltwater (Ganges, Indus, Mekong)
- Glacial till and outwash create fertile soils in periglacial zones
- Albedo: glacier surfaces reflect 50–90% of incoming solar radiation, cooling regional climates
An ice sheet is a continental-scale glacier covering more than 50,000 km². Only two exist today:
| Feature | Antarctic Ice Sheet | Greenland Ice Sheet |
|---|---|---|
| Area | 13.9 million km² | 1.7 million km² |
| Average thickness | ~2,160 m | ~1,790 m |
| Volume | ~26.5 million km³ | ~2.85 million km³ |
| Sea level equivalent if melted | ~58 m | ~7.2 m |
Ice sheets contain multiple ice streams — fast-moving corridors of ice draining into ice shelves floating on the ocean. When ice shelves collapse (e.g., Larsen B Ice Shelf, Antarctica, 2002), inland glaciers accelerate.
A forest is a land cover type dominated by trees with a canopy cover generally exceeding 10–30% (definitions vary). Key types relevant to VCE:
Tropical rainforests
- Located 0–10° latitude; >2,000 mm annual rainfall; mean temperature 25–28°C year-round
- Extraordinarily high biodiversity: Amazon contains ~10% of all species on Earth
- Multi-layered canopy (emergent, canopy, understorey, shrub, ground layers)
- Closed nutrient cycle: most nutrients are stored in biomass, not soil — clearing releases them temporarily but leaves infertile soils
Temperate forests
- 40–60° latitude; seasonal rainfall and temperature; deciduous or mixed
- Lower biodiversity than tropical but significant carbon storage
Boreal forest (taiga)
- 50–70°N; dominated by conifers (spruce, pine, fir, larch)
- World’s largest terrestrial biome by area (~17 million km²)
- Underlain by continuous or discontinuous permafrost
Forest ecosystem services
- Carbon sequestration: forests absorb ~2.6 billion tonnes of CO₂/year
- Water regulation: transpiration drives the hydrological cycle; Amazon forest generates 50–80% of its own rainfall through moisture recycling
- Biodiversity: forests harbour >80% of terrestrial species
- Climate regulation: latent heat release from transpiration cools regional temperatures
KEY TAKEAWAY: Glaciers and ice sheets are dynamic water stores shaped by the balance between accumulation and ablation; forests are complex ecosystems providing carbon, water and biodiversity services. Both are highly sensitive to temperature change.
EXAM TIP: For glaciers, know the terms accumulation, ablation, equilibrium line, firn, and albedo. For forests, know canopy layers, nutrient cycle, and ecosystem services. These terms lift generic responses to high-scoring analytical answers.
COMMON MISTAKE: Students often describe forests only in terms of trees. A complete answer acknowledges the full ecosystem — including soils, water cycle, fauna, and nutrient cycling — explaining why these characteristics make forests irreplaceable.
