Volcanoes are mountains with a vent from which molten material from deep within the earth can spew under the appropriate conditions. Volcanoes have existed for geologic eons, but many are no longer active. The number of volcanoes worldwide that earth scientists consider active—those that can erupt—was about five hundred in the mid-1990s. Volcanoes are usually located at the junction of the earth's lithospheric plates. In the United States most active volcanoes are located in Alaska or in Hawaii, which consists of a group of islands formed by earlier volcanic eruptions. The West Coast of the continental United States also has a relatively inactive volcanic zone. The two principal volcanoes in the United States are Mauna Loa and Kilauea, both in the Hawaiian island chain. Mauna Loa, the world's largest volcano, erupted most recently in 1975 and 1984. Kilauea is in almost continual eruption. Alaskan eruptions occurred in 1989, when Mount Redoubt, along Cook Inlet, southwest of Anchorage, erupted; in 1992, when Mount Spurr erupted; and in 1996, when an unnamed volcano on Augustine Island (also in Cook Inlet) erupted.
Table of Contents
Discussion and Analysis4
Types of Eruptions8
Volcanic Areas as a Source of Natural Resources12
List of Figures
This paper focuses on Volcanoes that are a principal agent of degassing of the interior of the Earth and other planets. They thought to be the main source of the Earth's atmosphere and hydrosphere, and thus they are a vital part of the sustainable Earth system. Volcanic activity has provided the air we breathe and the water that makes up most of our body mass. Volcanism also provides vital enrichment to the Earth's soils, particularly in tropical areas. In spite of the long-term benefits, the effects of eruptions can be seriously negative in the short run, so volcanoes can be considered a natural hazard that threatens life and property. The significance of this paper is that among natural hazards, volcanoes have caused far fewer deaths and damage to property historically than have floods, coastal hazards, and earthquakes and so considered hazards of local or minor rank by some people. The historic record may be misleading because it is brief compared with geologic time and because gigantic eruptions occur too rarely to have been accurately assessed and understood. There are at least 1,500 volcanoes that considered active in the world, and about 400 have erupted in the past century. Eruptions span at least eight orders of magnitude, ranging from erupted magma volumes of less than 10,000 m3 (cubic meters) to more than 1,000 km3 (cubic kilometers). But most eruptions are quite small in scale, and their hazards are quite localized to areas near the volcano. Larger eruptions known to have global impact, but because of their statistical rarity, the scientific understanding of these events is very limited. Understanding of the largest eruptions (super-eruptions) is the most limited, but these conceivably include worldwide loss of multiple growing seasons and huge global loss of life (volcanic winter).
The spatial and temporal distribution of volcanism on Earth's surface associated with ...