Effects of Volcano

Effects Of Volcanism and Prediction

Effects of Volcanism

  • Lava Flows Control of lava flows has been attempted with limited success by bombing flow fronts to attempt to divert the flow, and by spraying with water to cool the flow. The latter is credited with saving the fishing harbor during a 1973 eruption in Iceland.

  • Violent Eruptions and Pyroclastic Activity

  • Poisonous Gas Emissions

Secondary And Tertiary Effects Of Volcanism

  • Mudflows (Lahars)

  • Debris Avalanches and Debris Flows.

  • Flooding

  • Tsunamis

  • Volcanic Earthquakes and Tremors

  • Atmospheric Effects

  • Famine and Disease

Beneficial Aspects Of Volcanism

Volcanism throughout Earth history is responsible for outgassing of the Earth to help produce both the atmosphere and hydrosphere. Volcanism helps renew the soil, and soils around active volcanoes are some of 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. Predicting Volcanic Eruptions: Before discussing how we can predict volcanic eruptions, it is important to get some terminology straight by defining some commonly used terms. Active Volcano-An active volcano is a volcano that has shown eruptive activity within recorded history. Thus an active volcano need not be in eruption to be considered active.

  • Currently there are about 600 volcanoes on Earth considered to be active volcanoes.

  • Each year 50 to GO of volcanoes actually erupt. 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.

  • Yellowstone Caldera is about 600, 000 years old and is deeply eroded. But fumaroles activity hot springs, and geysers all point to the fact that magma still exists beneath the surface. Thus, Yellowstone Caldera is not considered extinct.

  • Other volcanoes that are deeply eroded smaller, and much younger than Yellowstone, that show no hydrothermal activity may be considered extinct. 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 past.

  • Because the lifetime of a volcano may be on the order of a million years, dormant volcanoes can become active volcanoes all of sudden. These are perhaps the most dangerous volcanoes because people living in the vicinity of a dormant volcano may not understand the concept of geologic time. And there is no written record of activity. These people are sometimes difficult to convince when a dormant volcano shows signs of renewed activity.

  • Yellowstone Caldera would be considered a dormant volcano.

  • Mount St. Helens was considered as a dormant volcano, having not erupted for 123 years, before its reawakening in 1980.

  • Mount Pinatubo in the Philippines had been dormant for over 400 years before its eruption in 1991.

  • Mount Vesuvius, near Naples, Italy was considered an extinct volcano prior to its devastating eruption of 79 A. D.

Long-Term Forecasting and Volcanic Hazards Studies

  • Studies of the geologic history of a volcano are generally necessary to make an assessment of the types of hazards posed by the volcano and the frequency at which these types of hazards have occurred in the past.

  • Once this information is available geologists can then make forecasts concerning what areas surrounding a volcano would be subject to the various kinds of activity should they occur in a future eruption and also make forecasts about the long-term likelihood or probability of a volcanic eruption in the area.

  • During such studies, geologists examine sequences of layered deposits and lava flows. Armed with knowledge about the characteristics of deposits left by various types of eruption a, the past behavior of a volcano can be determined.

  • Using radiometric age dating of the deposits the past frequency of events can be determined.

  • This information is then combined with knowledge about the present surface aspects of the volcano to make volcanic hazards maps which can aid other scientists, public officials, and the public at large to plan for evacuations, rescue and recovery in the event that short term prediction suggests another eruption.

  • Such hazards maps delineate zones of danger expected from the hazards discussed above: Lava flow s, pyroclastic flow s, tephra falls, mudflows, flood s, etc.

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.

  • Seismic Exploration and Monitoring: Since seismic waves are generated by both earthquakes and explosions, and since S-waves cannot pass through liquids, arrays of seismographs can be placed around a volcano and small explosions can be set off to generate seismic waves. If a magma body exists beneath the volcano, then there will l: e zone were no S-waves arrive (an S-wave shadow zone) that can be detected. Monitoring the movement of the S-wave shadow zone can delineate the position and movement of the magma body.

  • Changes in Magnetic Field-Rocks contain minerals such as magnetite that are magnetic. Such magnetic minerals generate a magnetic field. However, above a temperature called the Curie Temperature, these magnetic minerals show no magnetism. Thus, if a magma body enters a volcano, the body itself will show no magnetism, and if it heats the surrounding rocks to temperatures greater than the Curie Temperature (about 500° C for magnetite) the magnetic field over the volcano-will be reduced. Thus, by measuring changes in the magnetic field, the movement of magma can sometimes be tracked.

  • Changes in Electrical Resistivity-Rocks have resistance to the flow of electrical current which is highly dependent on temperature and water content. As magma moves into a volcano this electrical resistivity will decrease. Making measurements of the electrical resistivity by placing electrodes into the ground, may allow tracking of the movement of magma.

  • Ground Deformation-As magma moves into a volcano, the structure may inflate. This will cause deformation of the ground, which can be monitored. Instruments like tilt meters measure changes in the angle of the Earth s surface which are measured in microradians track changes in distance between several points on the ground to monitor deformation.

  • Changes in Groundwater System-As magma enters a volcano it may cause changes in the groundwater system, causing the water table to rise or fall and causing the temperature of the water to increase. By monitoring the depth to the water table in wells and the temperature of wells water, spring water, or fumaroles, changes can be detected that many signify a change in the behavior of the volcanic system. Changes in Heat Flow-Heat IS everywhere flowing out of the surface of the Earth. As magma approaches the surface or as the temperature of groundwater increases, the amount of surface heat flow will increase. Although these changes may be small they can be measured using infrared remote sensing.

  • Changes in Gas Compositions-The composition of gases emitted from volcanic vents and fumaroles often changes just prior to an eruption. In general, increases in the proportions of hydrogen chloride (Hel) and sulfur dioxide (SO2) are seen to increase relative to the proportion of water vapor.