Volcanoes have long been a source of both fascination and fear. Mankind has long been drawn to the majesty and power of the volcano while those living within its reach often live in fear of its destructive forces.
A volcano is defined as an opening, or rupture, in a planet’s surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity which involves the extrusion of rock can form mountains or features like mountains over a period of time.
Volcanoes are generally found where tectonic plates have pulled apart or come together. Volcanoes can also form where there is stretching and thinning of the Earth’s crust such as in the African Rift Valley, the Wells Gray-Clearwater Volcanic Field and the Rio Grande Rift in North America and the European Rhine Graben. Some volcanoes are also referred to as “mantle plumes” or “hotspots”, and these can occur far from plate boundaries such as those found in Hawaii. Hotspot volcanoes can also found elsewhere in the solar system, especially on rocky planets and moons.
The most common perception of a volcano is that of a conical mountain which is spewing lava and poisonous gases from a crater at its summit. This describes only one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of any particular volcano depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a single summit crater, whereas others present landscape features such as massive plateaus surrounding the vent. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash) and gases (mainly steam and magmatic gases) can be located anywhere on the surrounding landform. Many of these vents can give rise to smaller cones such as those found on Hawaii’s Kilauea.
There are other types of volcano some of which include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes are known to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.
There are other volcanoes known as Shield volcanoes, for their broad, shield-like profiles, which are formed by the eruption of low-viscosity lavas that can flow a great distance from a vent, but not generally explode catastrophically. The Hawaiian volcanic chain is considered a series of shield cones, and they are common in Iceland, as well.
Volcanoes are generally classified as dormant, active or extinct. Dormant volcanoes are those that are not currently active but could become restless or erupt again. Active volcanoes have recorded activity that dates from between the last 3000-10,000 years. Extinct volcanoes are those volcanoes that scientists consider unlikely to erupt ever again. But determining whether a volcano is truly extinct is often difficult.
Some notable volcanoes are-
Mauna Loa-Hawaii-This is the largest volcano on earth. Mauna Loa is an active shield volcano, with a volume estimated at approximately 18,000 cubic miles. The Hawaiian name “Mauna Loa” means “Long Mountain”. Lava eruptions from it are silica-poor, making it very fluid: and as a result eruptions tend to be non-explosive and the volcano has extremely shallow slopes. It’s last eruption was in 1984.
Santorini-Greece-This island is the site of one of the largest volcanic eruptions the planet has ever seen. It is believed to have happened some 3,500 years ago at the height of the Minoan civilization. The eruption left a large caldera that is surrounded by volcanic ash deposits hundreds of feet deep and may have led indirectly to the collapse of the Minoan civilization on the island of Crete, seventy miles to the south by the creation of a gigantic tsunami.
Mount Vesuvius-Italy-This volcano is a stratovolcano east of Naples, Italy. It is the only volcano on the European mainland to have erupted within the last hundred years. The last eruption was 1944. Vesuvius is best known for its eruption in 79 AD that led to the destruction of the Roman cities of Pompeii and Herculaneum. It has erupted many times since and is today regarded by many as one of the most dangerous volcanoes in the world because of the population of 3,000,000 people now living close to it.
Learn more with at these Volcanoes websites.