Volcano Questions and Answers
From the USGS
· What is a volcano?
Volcanoes are mountains, but they are very different from other mountains; they are not formed by folding and crumpling or by uplift and erosion. Instead, volcanoes are built by the accumulation of their own eruptive products -- lava, bombs (crusted over lava blobs), ashflows, and tephra (airborne ash and dust). A volcano is most commonly a conical hill or mountain built around a vent that connects with reservoirs of molten rock below the surface of the Earth. The term volcano also refers to the opening or vent through which the molten rock and associated gases are expelled. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.
· Where did the term "volcano" come from?
The word "volcano" comes from the little island of Vulcano in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano was the chimney of the forge of Vulcan -- the blacksmith of the Roman gods. They thought that the hot lava fragments and clouds of dust erupting form Vulcano came from Vulcan's forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars, the god of war. In Polynesia the people attributed eruptive activity to the beautiful but wrathful Pele, Goddess of Volcanoes, whenever she was angry or spiteful. Today we know that volcanic eruptions are not super-natural but can be studied and interpreted by scientists. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.
· What is an "eruption" ?
An eruption occurs when magma rises from its source or from a storage reservoir and finally reaches the Earth's surface. As it rises, the magma fractures overlying rocks, which causes earthquakes, and parts of the volcano deform as magma approaching the surface makes room for itself. -- From: Brantley and Topinka, 1984, Earthquake Information Bulletin, v.16, no.2.
· How much of the Earth is volcanic?
More than 80 percent of the Earth's surface -- above and below sea level -- is of volcanic origin. Gaseous emissions from volcanic vents over hundreds of millions of years formed the Earth's earliest oceans and atmosphere, which supplied the ingredients vital to evolve and sustain life. Over geologic eons, countless volcanic eruptions have produced mountains, plateaus, and plains, which subsequent erosion and weathering have sculpted into majestic landscapes and formed fertile soils. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.
· How many active volcanoes are there in the world?
About 500 active volcanoes are known on Earth, not counting those that lie beneath the sea. -- From: Tilling, 1980, Volcanoes: Earthquake Information Bulletin, v.12, n.4.
· What is the "Ring of Fire"?
Volcanoes are not randomly distributed over the Earth's surface. Most are concentrated on the edges of continents, along island chains, or beneath the sea forming long mountain ranges. More than half of the world's active volcanoes above sea level encircle the Pacific Ocean to form the circum-Pacific "Ring of Fire". -- From: Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· How many people are affected by volcanic eruptions?
Scientists have estimated that at least 200,000 persons have lost their lives as a result of volcanic eruptions during the last 500 years. Between 1980 and 1990, volcanic activity killed at least 26,000 people and forced nearly 450,000 to flee from their homes. -- From: Tilling, 1980, Volcanoes: Earthquake Information Bulletin, v.12, n.4, and Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· What are some positive products from volcanoes?
The Earth's crust, on which we live and depend, is in large part the product of millions of once-active volcanoes and tremendous volumes of magma that did not erupt but instead cooled below the surface. Such persistent and widespread volcanism has resulted in many valuable natural resources throughout the world. For example, volcanic ash blows over thousands of square kilometers of land increases soil fertility for forests and agriculture by adding nutrients and acting as a mulch. Groundwater heated by large, still-hot magma bodies can be tapped for geothermal energy. And over many thousands of years, heated groundwater has concentrated valuable minerals, including copper, tin, gold, and silver, into deposits that are mined throughout the world. -- From: Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· What was the largest volcanic eruption in the 20th century?"
The largest eruption in the world this century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6 -- (which is equivalent to 230 years of eruption at Kilauea (Hawaii) or, about 30 times the volume erupted by Mount St. Helens (Washington) in 1980.) -- From: Wright and Pierson, 1992, USGS Circular 1073, and Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication. )
· What was the most destructive volcanic eruption in the history of the United States?
The May 18, 1980 eruption of Mount St. Helens (Washington) was the most destructive in the history of the United States. Novarupta (Katmai) Volcano , Alaska, erupted considerably more material in 1912, but owing to the isolation and sparse population of the region affected, there were no human deaths and little property damage. In contrast, Mount St. Helens' eruption in a matter of hours caused loss of lives and widespread destruction of valuable property, primarily by the debris avalanche, the lateral blast, and the mudflows. -- From: Tilling et.al., 1990, The Eruptions of Mount St. Helens: vPast, Present, and Future: USGS Information Publication.
· Where is the largest active volcano in the world?
Mauna Loa (Hawaii) is the world's largest active volcano, projecting 13,677 feet above sea level, its top being over 28,000 feet above the deep ocean floor. From its base below sea level to its summit, Mauna Loa is taller than Mount Everest. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication, and Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· Where in the United States is there evidence of volcanism?
Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits. A thick ash deposit sandwiched between layers of sandstone in Nebraska, the massive granite peaks of the Sierra Nevada mountain range, and a variety of volcanic layers found in eastern Maine are but a few of the striking clues of past volcanism. -- From: Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· Where does the United States rank in the number of volcanoes?
The United States ranks third, behind Indonesia and Japan, in the number of historically active volcanoes (that is, those for which we have written accounts of eruptions). In addition, about 10 percent of the more than 1,500 volcanoes that have erupted in the past 10,000 years are located in the United States. Most of these volcanoes are found in the Aleutian Islands, the Alaska Peninsula, the Hawaiian Islands, and the Cascade Range of the Pacific Northwest. -- From: Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.
· What GOOD is a volcano?
Over the long term and geologic time, volcanic eruptions and related processes have directly and indirectly benefited mankind. Volcanic materials ultimately break down and weather to form some of the most fertile soils on Earth, cultivation of which has produced abundant food and fostered civilizations. People use volcanic products, the internal heat associated with young volcanic systems has been harnessed to produce geothermal energy, and most of the metallic minerals mined in the world, such as copper, gold, silver, lead, and zinc, are associated with magmas found deep within the roots of extinct volcanoes. -- From: Kious and Tilling, 1996, This Dynamic Earth: The Story of Plate Tectonics: USGS General Interest Publication, and Tilling, 1985, Volcanoes: USGS General Interest Publication