This impressive scientific resource presents up-to-date information on ten thousand years of volcanic activity on Earth. Lee Siebert has compiled data on the world's volcanoes since 1974 and was Director of the Smithsonian's Global Volcanism Program (GVP) from 2007 to 2010. Although volcanoes are all made from hot magma reaching the surface of the Earth and erupting, there are different kinds.
When it finally reaches the surface, it erupts out of the ground as lava, ash, volcanic gasses and rock. An active volcano is one that has had an eruption in historical times (in the last few thousand years). Somewhere, around the world, there are likely about 20 active volcanoes erupting as you’re reading this.
Three quarters of all eruptions happen underneath the ocean, and most are actively erupting and no geologist knows about it at all.
Geologists measure volcano eruptions using the Volcano Explosivity Index, which measures the amount of material released. The tallest volcano on Earth is Hawaii’s Mauna Kea, with an elevation of 4,207 meters. You might think that the peak of Mount Everest is the most distant point from the center of the Earth, but that’s not true.
Although Mauna Loa has historically been considered to be the largest volcano on Earth, in reality it is not the largest.

In the decade and a half since the previous edition was published new studies have refined assessments of the ages of many volcanoes, and several thousand new eruptions have been documented. Shield volcanoes have lava flows with low viscosity that flow dozens of kilometers; this makes them very wide with smoothly sloping flanks. Cinder cone volcanoes are usually smaller, and come from short-lived eruptions that only make a cone about 400 meters high. A dormant volcano is one that has erupted in historical times and has the potential to erupt again, it just hasn’t erupted recently.
For example, the cinder cone volcano Paricutin appeared in a Mexican cornfield on February 20, 1943. One of the reasons is that volcanoes occur at the mid ocean ridges, where the ocean’s plates are spreading apart. Some of the most deadly volcanoes include Krakatoa, which erupted in 1883, releasing a tsunami that killed 36,000 people. Vesuvius, captured in 2000 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite. The most dangerous aspect of volcanoes are the deadly pyroclastic flows that blast down the side of a volcano during an eruption. Olympus Mons, on Mars, is a giant shield volcano that rises to an elevation of 27 km, and it measures 550 km across. It’s only a little bigger than the largest volcano on Earth, Mauna Loa with an elevation of only 4,169 meters.

Tom Simkin (1933-2009), served as GVP founder and director from 1968-1995 in a distinguished career in volcanology that spanned more than four decades.
Within a week it was 5 stories tall, and by the end of a year it had grown to more than 336 meters tall.
If you add the underwater volcanoes, you get an estimate that there are a total of about 6,000 volcanoes that have erupted in the last 10,000 years.
When Vesuvius exploded in AD 79, it buried the towns of Pompeii and Herculaneum, killing 16,000 people.
These contain ash, rock and water moving hundreds of kilometers an hour, and hotter than 1,000 degrees C. Scientists think that Olympus Mons was able to get so large because there aren’t any plate tectonics on Mars. This edition also includes new photographs, data on the most common rock types forming each volcano, information on population densities near volcanoes, and other features, making it the most comprehensive source available on Earth's dynamic volcanism.
This magma is lighter than the surrounding rock, so it rises up, finding cracks and weakness in the Earth’s crust. A single hotspot was able to bubble away for billions of years, building the volcano up bigger and bigger.

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