Volcano facts for kids
The Earth's crust is broken into 17 major, rigid tectonic plates. These float on a hotter, softer layer in its mantle. Volcanoes are often found where tectonic plates are moving apart or coming together. Volcanoes can also form where there is stretching and thinning of the crust's plates, e.g., in the East African Rift. Volcanoes are usually not found where two tectonic plates slide past one another.
Volcanism away from plate boundaries is caused by mantle plumes. These so-called "hotspots", for example Hawaii, are thought to arise from upwelling magma from the core–mantle boundary, 3,000 km deep in the Earth.
When there is enough pressure, the volcano erupts. Some volcanic eruptions blow off the top of the volcano. Sometimes, the magma comes out quickly and sometimes it comes slowly. Some eruptions come out at a side instead of the top.
Volcanologists are scientists who study volcanoes using methods from geology, chemistry, geography, mineralogy, physics and sociology.
The world's biggest volcano is named Mauna Loa in Hawaii. Mauna Loa is part of the five volcanoes on Hawaii's 'Big Island'. The most recent time this volcano erupted was in 1984. It erupted 33 times in the last 170 years. Like all the other Hawaiian volcanoes, Mauna Loa was created by the movement of the Pacific tectonic plate which moved over the Hawaii hotspot in the Earth's mantle. Mauna Loa is 4,196 meters tall. It is a shield volcano. The largest recent eruption from Mauna Loa left a lava trail 51 kilometres (32 miles) long.
Types of volcanoes
Shield volcanoes are built out of layers of lava from continual eruptions (without explosions). Because the lava is so fluid, it spreads out, often over a wide area. Shield volcanoes do not grow to a great height, and the layers of lava spread out to give the volcano gently sloping sides. Shield volcanoes can produce huge areas of basalt, which is usually what lava is when cooled.
The base of the volcano increases in size over successive eruptions where solidified lava spreads out and accumulates. Some of the world's largest volcanoes are shield volcanoes.
Unlike shield volcanoes, stratovolcanoes have a steep profile and periodic eruptions. The lava that flows from stratovolcanoes cools and hardens before spreading far. It is sticky, that is, it has high viscosity. The magma forming this lava is often felsic, with high-to-intermediate levels of silica, and less mafic magma. Big felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).
Two famous stratovolcanoes are Japan's Mount Fuji, and Vesuvius. Both have big bases and steep sides that get steeper and steeper as it goes near the top. Vesuvius is famous for its destruction of the towns Pompeii and Herculaneum in 79 AD, killing thousands.
A caldera is a basin-like feature formed by collapse of land after a volcanic eruption. This happens after a huge stratovolcano blows its top off. The base of the crater then sinks, leaving a caldera where the top of the volcano was before. Krakatoa, best known for its catastrophic eruption in 1883, is much smaller now.
How volcanoes are formed
There are two main processes.
Volcanoes are made when two tectonic plates come together. When these two plates meet, one of them (usually the oceanic plate) goes under the continental plate. This is the process of subduction. Afterwards, it melts and makes magma (inside the magma chamber), and the pressure builds up until the magma bursts through the Earth's crust.
The second way is when a tectonic plate moves over a hot spot in the Earth's crust. The hot spot works its way through the crust until it breaks through. The caldera of Yellowstone Park was formed in that way; so were the Hawaiian Islands.
A traditional way to classify or identify volcanoes is by its pattern of eruptions. Those volcanoes which may erupt again at any time are called active. Those that are now quiet called dormant (inactive). Those volcanoes which have not erupted in historical times are called extinct.
in French dormant means en sommeil
Extinct (dead volcano)
An extinct volcano has not erupted in the past 10,000 years. Edinburgh Castle in Scotland is located on top of an extinct volcano.
- Kilauea (Hawaii, USA)
- Krakatoa (Rakata, Indonesia)
- Mauna Loa (Hawaii, USA)
- Mauna Kea (Hawaii, USA)
- Mount Ashitaka (Japan)
- Mount Baker (Washington, USA)
- Mount Edziza (British Columbia, Canada)
- Mount Etna (Sicily, Italy)
- Mount Erebus (Ross Island, Antarctica)
- Mount Hood (Oregon, USA)
- Mount Fuji (Honshu, Japan)
- Mount Rainier (Washington, USA)
- Mount Ruapehu (North Island, New Zealand)
- Mount Shasta (California, USA)
- Mount St. Helens (Washington, USA)
- Novarupta (Alaska, USA)
- Olympus Mons (Mars (planet))
- Popocatépetl (Mexico-Puebla state line, Mexico)
- Surtsey (Surtsey island, Iceland)
- Santorini (Santorini island, Greece)
- Tambora (Sumbawa, Indonesia)
- Teide (Tenerife, Canary Islands, Spain)
- Vesuvius (Gulf of Naples, Italy)
- Whakaari/White Island (New Zealand)
- Yellowstone Caldera (Wyoming, USA)
Largest volcano on Earth
The Earth's largest volcano has been discovered. It is 2 km below the sea on an underwater plateau known as the Shatsky Rise. This is about 1,600 km east of Japan. The previous record-holder, Mauna Loa in Hawaii, is still the largest volcano on land.
The 310,000 km2 (119,000 sq mi) volcano, Tamu Massif, is comparable in size to Mars' vast Olympus Mons volcano, which is the largest in the Solar System. It was formed about 145 million years ago when massive lava flows erupted from the centre of the volcano to form a broad, shield-like feature. That suggests the volcano produced a flood basalt eruption.
The Tamu Massif extends some 30 km (18 miles) into the Earth's crust. The researchers doubted the submerged volcano's peak ever rose above sea level during its lifetime and say it is unlikely to erupt again.
- "The bottom line is that we think that Tamu Massif was built in a short (geologically speaking) time of one to several million years and it has been extinct since," co-author William Sager, of the University of Houston told the AFP news agency.
- "There were lots of oceanic plateaus (that) erupted during the Cretaceous period (145-65 million years ago) but we don't see them since. Scientists would like to know why... The biggest oceanic plateau is Ontong Java plateau, near the equator in the Pacific, east of the Solomon Islands. It is much bigger than Tamu – it's the size of France".
Images for kids
A 2007 eruptive column at Mount Etna producing volcanic ash, pumice and lava bombs
Santa Ana Volcano, El Salvador. A close-up aerial view of the nested summit calderas and craters, along with the crater lake.
Skjaldbreiður, a shield volcano whose name means "broad shield"
Izalco (volcano), located in the Cordillera de Apaneca volcanic range complex in El Salvador. Only a few generations old, Izalco is the youngest and best known cone volcano. Izalco erupted almost continuously from 1770 (when it formed) to 1958, earning it the nickname of "Lighthouse of the Pacific".
Pāhoehoe lava flow on Hawaii. The picture shows overflows of a main lava channel.
San Miguel (volcano), El Salvador. On December 29, 2013, San Miguel volcano, also known as "Chaparrastique", erupted at 10:30 local time, spewing a large column of ash and smoke into the sky; the eruption, the first in 11 years, was seen from space and prompted the evacuation of thousands of people living in a 3 km radius around the volcano.
Ash plume from San Miguel (volcano) "Chaparrastique", seen from a satellite, as it heads towards the Pacific Ocean from the El Salvador Central America coast, December 29, 2013
Lava flows at Holuhraun, Iceland, September 2014
Ash plume rising from Eyjafjallajökull on April 17, 2010
Volcano Facts for Kids. Kiddle Encyclopedia.