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9.2 Tectonic impacts: 5. Plate tectonics and climate

Syllabus reference (October 2002 version)
5. Plate tectonics and climate	*Students learn to:* predict the possible effects of explosive volcanic activity on global and local climates describe and explain the potential and observed impacts of volcanic eruptions on global temperature and agricture	*Students:* identify data, choose resources, gather and analyse secondary data on recent volcanic activity to determine the relationship between the eruption of ash and gas from an explosive volcanic eruption and the subsequent decrease in global temperature

Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.
[Edit: 24 Jul 08]

Prior learning: Preliminary modes 8.2 (subsections 3, 4 and 5) and 8.5 (subsections 2 and 3); Stage 5, Outcome 5.9.

identify data, choose resources, gather and analyse secondary data on recent volcanic activity to determine the relationship between the eruption of ash and gas from an explosive volcanic eruption and the subsequent decrease in global temperature

This investigation can be conducted using scientific papers, such as the one relating to the 1991 eruption of Mount Pinatubo referenced below.

The Atmospheric Impact of the 1991 Mount Pinatubo Eruption A paper written by Stephen Self, Jing-Xia Zhao, Rick E. Holasek, Ronnie C. Torres, and Alan J. King, published by USGS, Chris Newhall, 6/11/1999. Most of the information you need is in the Abstract of the paper.

Mount Pinatubo by Clayton L Sneed, USGS 21/5/2001

In deciding the type of data necessary for this investigation, you need to:
1. select an explosive volcanic eruption that has been identified as one that may have affected global temperature
2. consider the type of information about the eruption that must be gathered
3. consider the information about global temperatures that must be gathered.
In choosing resources, determine the suitability and effectiveness of your browser search facilities to locate the relevant information.
Gather the information by using the browser features to locate the type of data you have identified as useful.
Analyse the information to make a generalisation regarding the eruption of ash and gas and the subsequent decrease in global temperature. You can justify the generalisation by seeking evidence for similar relationships in other recent eruptions.

Other sites providing information about recent volcanoes that may have caused global temperature change:

El Chichon, 1982 , Michigan Technological University, Houghton, Michigan, USA.
Mt St Helens, 1980 , Angelfire.com

describe and explain the potential and observed impacts of volcanic eruptions on global temperature and agricture

The potential impacts of volcanic eruptions on global temperature:

The injection of sulfur dioxide (SO₂ ) into the stratosphere causes the greatest impact on the atmosphere and global temperatures. The SO₂ converts to sulfuric acid aerosols that block incoming solar radiation and contribute to ozone destruction. The reduction in solar radiation can cause global cooling. The plume of ash from an eruption causes an increase in the amount of sunlight reflected by the Earth's atmosphere back to space causing the surface of the planet to cool.

The potential impacts of volcanic eruption on agricture:

Volcanic eruptions have the potential to devastate agrictural activity. Areas close to the erupting cone can be destroyed by lava and mud flows. Poisonous gases can kill herds of stock. Areas further from the cone can be covered in thick layers of pyroclastic debris.

The observed impacts of volcanic eruption on global temperature:

El Chichon and Mount Pinatubo emitted the greatest amounts of SO₂into the stratosphere. El Chichon produced about 7 million tonnes of SO₂and Mount Pinatubo produced about 20 million tonnes. Both of these volcanoes are at low latitudes but they both had high eruption rates. The impact of eruptions may not last very long. For a large eruption like Mount Pinatubo, the impact may last for up to three years.

The observed impacts of volcanic eruption on agricture:

Mt St Helens produced a layer of debris six-tenths of an inch (about 15mm) thick, five hundred miles (about 800km) away. In the regions affected by Mt St Helens:
- crop loss was estimated at $100 million, or seven percent of the national crop value for that region.
- fifty percent of the alfalfa hay crop was ruined
- timber to the value of $100 million dollars was destroyed
- the wheat, potato, and apple crops were above normal, through a decrease in popations of destructive insects.

predict the possible effects of explosive volcanic activity on global and local climates

Global effects:

Explosive volcanism will produce large amounts of ash and aerosols that can reach into the stratosphere. The high levels of material in the atmosphere at this height will rest in a reduced amount of radiation from the sun reaching the Earth’s surface. Less radiation reaching the surface reduces the surface temperature and the heating of air in contact with the surface. If widespread enough, there will be a reduction in the global temperature.

Local effects:

Fine ash will increase precipitation in the area around a volcano.
The precipitation will be acidic because of the reaction of sfur dioxide with water in clouds developing around the volcano.
There may be reduced local temperatures because of reduced radiation if a volcanic plume persists for a prolonged time.