FQ 4. What are the effects of a volcanic eruption on the natural environment?

4.1 Effects of a volcanic eruption on topography

Topography: shape of the land will change as landforms are destroyed and built…

• The land is built up, as layers of tephra, lava, lahar and pyroclastic flows are deposited
• The topes of volcanic cones can collapse or blow up (depending on eruption kind)
• New craters or caldera can form, some filling with water (Ruapehu crater lakes)
• The flanks of old volcanic cones can erode leaving the hard plug expose

EG. During the Mt Ruapehu eruption in 1995, the shape of the crater lake was changed due to the explosion of the plug. The explosion and lahars also helped to change the topography of the peak of Mt Ruapehu.

4.2 Effects of a volcanic eruption on drainage

Drainage: rivers and lakes change…

• Rivers can be diverted if volcanic material blocks old river courses
• A change in the topography (shape of the land) can change drainage patterns (under ground water drainage)
• Lahars can flow into rivers, raising the water level (Tangiwai Disaster, 1953)
• Waterways may become polluted with ash

EG. During the Mt Ruapehu eruption in 1995, ash contaminated rivers and streams. The Whangaehu River was swollen by the lahars that entered it. The Yellow and Grey lakes on Mt Ruapehu became interconnected after the eruption.

4.3 Effects of a volcanic eruption on vegetation

Vegetation: forests and grass lands will disappear…

• Close to the eruption vegetation can be blown over or burnt as a result of lava and pyroclastic flows
• Vegetation can be covered in ash

EG. During the Mt Ruapehu eruption in 1995, ash covered native forests in the area burning some trees and bushes.

4.4 Effects of a volcanic eruption on soils

Soil: composition changes…

• Areas receiving volcanic ash will often enjoy an increase in soil fertility
• Areas receiving scoria or pumice will develop as well-drained soil
• Too much volcanic material can create a soil deficient in cobalt, making it unsuitable for farming (Volcanic Plateau, Central NI)

EG. During the Mt Ruapehu eruption in 1995, ash covered existing soil. This has contaminated the soil surrounding Mt Ruapehu and limits what can be grown in the area.

4.5 Effects of a volcanic eruption on fauna

Fauna: wildlife may die…

• Wildlife may die if caught in the lava flows and the eruption
• Wildlife may struggle to find food and water after eruption
  

EG. During the Mt Ruapehu eruption in 1995, fish died in waterways due to ash contaminated streams and rivers.

4.6 Effects of a volcanic eruption on the atmosphere

Atmosphere: ash contaminates the air.

EG. During the Mt Ruapehu eruption in 1995, ash was found 140km away from the eruption.

Each of these effects need diagrams.

See Mrs O'Hagan for notes on the effects of the Mt Tarawera eruption.