EENS 3050 | Natural Disasters |
Tulane University | Prof. Stephen A. Nelson |
Volcanic Hazards & Prediction of Volcanic Eruptions |
Volcanic Hazards This lecture will begin with a video entitled "Understanding Volcanic Hazards". This video was prepared by the International Association of Volcanology and Chemistry of the Earth's Interior in several languages, and was designed show people living in the vicinity of volcanoes the possible effects of an eruption. Although the terminology may vary slightly from what we have learned in this course, the effects are the same and the footage of volcanic eruptions in progress is spectacular. The video is dedicated to the 23,000 people who died as a result of mudflows (lahars) from the 1985 eruption of Nevado del Ruiz volcano in Colombia, and is intended to help prevent similar disasters in the future. The video covers:
Primary Effects of Volcanism
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Secondary and Tertiary Effects of Volcanism
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Over the last 500 years, volcanoes have directly or indirectly been responsible for over 275,000 deaths. The greatest killers have been pyroclastic flows, tsunami, lahars, and famine. |
Beneficial Aspects of Volcanism Since this course concentrates on the damaging effects of volcanism, we won't spend too much time on the topic of the beneficial aspects of volcanism. We note here, that volcanism throughout Earth history is responsible for outgasing of the Earth to help produce both the atmosphere and hydrosphere. Volcanism helps renew the soil, and soils around active volcanoes are some the richest on Earth. Hydrothermal processes associated with volcanism produce rich ore deposits, and the heat rising around magma bodies can sometimes be tapped to produce geothermal energy. Mitgation of Volcanic Disasters The best mitigation against casualties from volcanic eruptions is to provide warning based on eruption forecasts and knowledge of the past behavior of the volcano, and call for evacuations. Little can be done to protect property as the energy involved in volcanic eruptions is too great and few structures will survive if subjected to volcanic processes. As volcanic ash in the atmosphere has been known to cause problems with airplanes, a system currently exists to keep aircraft out of ash clouds. This can have severe economic consequences as evidenced by the near shutdown of European airports during the 2010 eruption of a volcano in Iceland. Because evacuation plans rely on knowledge of when the volcano might erupt and how it will behave when it does erupt, we will next discussion predicting volcanic eruptions and volcanic behavior. |
Predicting Volcanic Eruptions and Volcanic Behavior Before discussing how we can predict volcanic eruptions, its important to get some terminology straight by defining some commonly used terms. Active Volcano - An active volcano to volcanologists is a volcano that has shown eruptive activity within recorded history. Thus an active volcano need not be in eruption to be considered active.
Extinct Volcano - An extinct volcano is a volcano that has not shown any historic activity, is usually deeply eroded, and shows no signs of recent activity. How old must a volcano be to be considered extinct depends to a large degree on past activity.
Dormant Volcano - A dormant volcano (sleeping volcano) is somewhere between active and extinct. A dormant volcano is one that has not shown eruptive activity within recorded history, but shows geologic evidence of activity within the geologic recent past.
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Long - Term Forecasting and Volcanic Hazards Studies
Short - Term Prediction based on Volcanic Monitoring Short - term prediction of volcanic eruptions involves monitoring the
volcano to determine when magma is approaching the surface and monitoring for precursor
events that often signal a forthcoming eruption. |
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As noted above, as magma moves and deforms rocks it may be responsible for the
generation of earthquakes. Thus, there is usually an increase in seismic activity prior to
a volcanic eruption. Focal depths of these precursor earthquakes may change with
time, and if so, the movement of magma can sometimes be tracked. In addition,
volcanic tremor, as noted above, can also be indication that magma is moving below the
surface. |
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In general, no single event can be used to predict a volcanic eruption, and thus many
events are usually monitored so that taken in total, an eruption can often be
predicted. Still, each volcano behaves somewhat differently, and
until patterns are recognized for an individual volcano, predictions vary in their
reliability. Furthermore, sometimes a volcano can erupt with no precursor events at all. After the catastrophic eruption of Mount St. Helens on May 18, 1980, a volcanic dome began to grow in the crater. Growth of this dome occurred sporadically, and sometimes small eruptions occurred from the dome. After several years of dedicated monitoring, scientists are now able to predict with increasing accuracy eruptions from this dome. An example is shown in the graphs to the right. In the weeks prior to an eruption on March 19, 1982, the amount of seismic energy released increased, the amount dome expansion increased, tilt increased, and SO2 emissions increased prior to the event. |
Beginning on March 12, a prediction was made that an eruption would be likely within the next 10 days. On March 15, the prediction was narrowed to likely within 4 days, and on March 18 scientists predicted that an eruption would occur within the next two days. On March 19 the eruption did occur. Note that eruption predictions such as in this example are only possible if constant monitoring of a volcano takes place. Monitoring is an expensive endeavor, and not all active or potentially active volcanoes are monitored. Still, if people living around volcanoes are aware of some of the precursor phenomena that occur, they may be able to communicate their findings of anomalous events to scientists who can begin monitoring on a regular basis and help prevent a pending disaster. Education and communication is essential in reducing risk from volcanic hazards! |
Examples of questions on this material that could be asked on an exam
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