Why do volcanoes erupt facts

An active volcano is one that has had an eruption in historical times in the last few thousand years. Although some volcanoes can take thousands of years to form, others can grow overnight. For example, the cinder cone volcano Paricutin appeared in a Mexican cornfield on February 20, Within a week it was 5 stories tall, and by the end of a year it had grown to more than meters tall.

It ended its grown in , at a height of meters. Some are experiencing new activity, others are ongoing. Between volcanoes erupted last year, and were active in the last decade. Geologists estimate that 1, erupted in the last 10, years. Three quarters of all eruptions happen underneath the ocean, and most are actively erupting and no geologist knows about it at all. If you add the underwater volcanoes, you get an estimate that there are a total of about 6, volcanoes that have erupted in the last 10, years.

But then you knew that. Standing a whopping 4,m tall , this geological giant last erupted in Other planets and moons have volcanoes, too! The largest volcano in our solar system is Olympus Mons , found on Mars.

Incredibly, the ash deposits preserved the town and the remains of the people within it. Over time, lava and ash break down to produce nutrient-rich soil , great for growing crops! Maleo birds bury their eggs in the sand or soil near volcanoes to keep them warm. When the chicks hatch they claw their way up to the surface! In this situation, a zone of magmatic activity —or a hotspot—in the middle of a tectonic plate can push up through the crust to form a volcano.

Although the hotspot itself is thought to be largely stationary, the tectonic plates continue their slow march, building a line of volcanoes or islands on the surface. This mechanism is thought to be behind the Hawaii volcanic chain. Some 75 percent of the world's active volcanoes are positioned around the ring of fire , a 25,mile long, horseshoe-shaped zone that stretches from the southern tip of South America across the West Coast of North America, through the Bering Sea to Japan, and on to New Zealand.

This region is where the edges of the Pacific and Nazca plates butt up against an array of other tectonic plates. Importantly, however, the volcanoes of the ring aren't geologically connected. In other words, a volcanic eruption in Indonesia is not related to one in Alaska, and it could not stir the infamous Yellowstone supervolcano.

Volcanic eruptions pose many dangers aside from lava flows. It's important to heed local authorities' advice during active eruptions and evacuate regions when necessary.

One particular danger is pyroclastic flows, avalanches of hot rocks, ash, and toxic gas that race down slopes at speeds as high as miles an hour. Such an event was responsible for wiping out the people of Pompeii and Herculaneum after Mount Vesuvius erupted in A.

Similarly, volcanic mudflows called lahars can be very destructive. These fast-flowing waves of mud and debris can race down a volcano's flanks, burying entire towns. Ash is another volcanic danger. Unlike the soft, fluffy bits of charred wood left after a campfire, volcanic ash is made of sharp fragments of rocks and volcanic glass each less than two millimeters across. The ash forms as the gasses within rising magma expand, shattering the cooling rocks as they burst from the volcano's mouth.

It's not only dangerous to inhale , it's heavy and builds up quickly. Volcanic ash can collapse weak structures, cause power outages, and is a challenge to shovel away post-eruption. Volcanoes give some warning of pending eruption, making it vital for scientists to closely monitor any volcanoes near large population centers.

Warning signs include small earthquakes, swelling or bulging of the volcano's sides, and increased emission of gasses from its vents. None of those signs necessarily mean an eruption is imminent, but they can help scientists evaluate the state of the volcano when magma is building.

However, it's impossible to say exactly when, or even if, any given volcano will erupt. These two important gases are not poisonous. Sulfur dioxide, hydrogen chloride, and hydrogen fluoride are emitted, as well.

They are strong poisons and cause pollution problems. What kinds of rocks do volcanoes make? Volcanoes make many different types of rocks. For example, black shiny rocks with only a few crystals are usually basalt. The opposite — white shiny rock with many crystals and often many bubble holes inside the rock is rhyolite.

In between are andesites, which are light gray and usually have large box-shaped crystals called plagioclase. They come from the Andes Mountains, which is a chain of volcanoes in South America. The Hawaiian islands are mostly made up of basalts, so they are famous for their beautiful black-sand beaches.

How many volcanoes have been identified in the world? We know of at least 1, active volcanoes around the world. That is a big increase from the number that we used to think was correct. It means that more people are searching the earth for them. A graph of the number of volcanoes of the world shows that it goes up just about as fast as the number of people on the earth does. What country has the most volcanoes? Indonesia has the most volcanoes, by far.

It is really a special place because there seem to be volcanoes all around, in all directions. Merapi which means "mountain of fire" erupted in January and killed a few hundred people. How many volcanoes are there in the United States? The lower 48 states in the U. In Alaska, the number is more like When we talk about whether a volcano is active or potentially a threat, it is important to look at the past ten years.

Most of the important eruptions and disasters have happened at mountains that were not even recognized as being volcanoes, for example Pinatubo Philippines, , El Chichon Mexico, , Arenal Costa Rica, Are there any volcanoes in the U.