Measurement and Prediction of Volcanoes (Leaving Cert Geography): Revision Notes
Measurement and Prediction of Volcanoes
Predicting volcanic eruptions presents enormous challenges because every volcano behaves differently and displays unique warning signals before erupting. Successful prediction depends on volcanologists carefully monitoring the vital signs of a volcano. Despite these complexities, volcanic prediction has improved dramatically in recent decades.
Notable successes include the accurate forecasting of eruptions at Mount St Helens in 1980, Mount Pinatubo in 1992, and Mount Merapi in 2010. These predictions helped save thousands of lives in communities near these volcanoes.
Instruments used and eruption indicators
Volcanologists employ various sophisticated instruments and tools to detect and record volcanic activity patterns that may signal an approaching eruption.
Seismic activity
Earthquake activity: The increase in seismic activity beneath a volcano prior to an eruption, caused by magma movement through the Earth's crust.
Earthquake activity consistently increases beneath volcanoes before eruptions occur. Scientists use seismometers and seismographs to measure movements within the Earth's crust, detecting and recording these earthquakes. Seismometers must be positioned within a 20-kilometre radius of a volcano's vent for effective monitoring.
The precise placement of seismometers proves critical because many pre-eruption earthquakes are extremely small and difficult to detect. If seismometers are positioned too far from the volcano, these subtle earthquake signals could go unnoticed.
These earthquakes happen when magma and volcanic gases push their way upwards through cracks and vents in the crust. As magma rises towards the surface, it causes surrounding rock to vibrate, triggering earthquakes.
These seismic events serve as important warning signs that an eruption may be approaching. This monitoring method was successfully used to predict the eruption of Mount Pinatubo.
Ground deformation
Ground deformation: Changes in the natural shape of a volcanic mountain caused by pressure from rising magma and gases.
Ground deformation represents one of the most obvious indicators that a volcano approaches eruption. As pressure from rising magma and gases increases, volcanic mountain peaks swell shortly before eruption.
Scientists use several technologies to monitor ground deformation:
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Electronic Distance Measurement (EDM) devices measure any horizontal movement of a volcano. These devices send laser signals to reflectors which then return the signal. If the volcano expands or contracts, the signal takes longer or shorter time to return.
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Tiltmeters function similarly to a carpenter's spirit level, using a small bubble in water to detect changes in slope level. Even slight changes in the slope angle on a volcanic mountain indicate pressure build-up inside the volcano. Tiltmeters were used to monitor Mount St Helens before its eruption in 1980.
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GPS satellites monitor the Earth's surface, recording any changes in volcanic shape over time.
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Satellite radar (Interferometric Synthetic Aperture Radar - InSAR) captures images of volcanoes, allowing volcanologists to accurately record deformation changes in volcanic mountains.
Gas emissions
Carbon dioxide () sensors measure the release of from volcanoes. Gas releases from volcanoes can result in significant loss of life, as demonstrated by the disaster at Lake Nyos, Cameroon in 1986.
Case study: Lake Nyos disaster
Case Study: The Lake Nyos Disaster
Location: Lake Nyos, Cameroon
Date: 21st August 1986
Background: Lake Nyos is a water-filled crater formed from a volcanic eruption over 500 years ago.
The disaster: Large deposits of carbon dioxide seeped from the lake bottom, killing over 1,700 people and 3,500 livestock. The heavier-than-air gas flowed down valleys, suffocating everything in its path.
Response: Scientists discovered substantial deposits remained deep in the crater. In 2001, they decided to degas the lake using an electric pump system designed to mimic natural eruption effects. Vertical pipes now connect the lake bottom to the surface, with water near the bottom saturated in . This water is continuously pumped to the surface, releasing into the atmosphere in small, safe amounts.
Impact on volcanic prediction: Since this disaster, monitoring gas emissions has become a regular component of volcanic prediction systems worldwide.
Historical records
Historical records help predict when eruptions may occur again. When volcanologists understand a volcano's eruption history, they can combine this knowledge with information gathered from modern instruments to provide reasonably accurate predictions of future eruptions.
By studying patterns of past volcanic activity alongside current monitoring data, scientists can identify trends and cycles that may indicate when the next eruption is likely to happen. This approach proves particularly valuable for volcanoes with well-documented eruption histories.
Key Points to Remember:
- Volcanic prediction combines multiple monitoring methods including seismic activity, ground deformation, gas emissions, and historical records
- Seismometers must be placed within 20km of a volcano's vent to detect small pre-eruption earthquakes effectively
- Ground deformation is one of the most obvious signs of an approaching eruption as rising magma causes mountains to swell
- Gas monitoring became crucial after the Lake Nyos disaster in 1986 killed over 1,700 people from emissions
- Modern volcanic prediction has achieved notable successes, saving thousands of lives through accurate forecasting of eruptions at Mount St Helens, Mount Pinatubo, and Mount Merapi