A mountain with a center of hot magma is called a volcano. Under the right circumstances, volcanoes erupt and release a flow of lava. When this happens, they are as beautiful as they are scary and dangerous. Although most people recognize images of erupting volcanoes, they may not know a lot about them. Fortunately, there are a lot of interesting facts that can help you understand volcanoes, what makes them erupt, and what happens when they do.

How Are Volcanoes Made?

Magma lies in Earth’s mantle. Above that, the earth’s crust is broken into plates that float over the mantle. At times, magma seeps upwards through the plates when they move. When this magma reaches the surface, it turns to lava and ash, and when cooled, it forms a volcano as it hardens. With repeated eruptions, volcanoes will grow in size.

The Different Volcano Stages

Volcanoes fall into one of three categories: active, dormant, or extinct. When a volcano is active, it is ready to erupt and it has also had a recent eruption. When a volcano is likely to have a future eruption but hasn’t in a very long time, it is considered dormant. If thousands of years have passed since a volcano has erupted and there are no signs that it will do so again, it is classified as extinct.

How Do Volcanoes Erupt, and What Does Plate Tectonics Have to Do With it?

Volcanoes erupt when plates of Earth’s crust move. This movement can create gaps or cracks near the edges of the plates. Plate tectonics is a theory that describes how the crust of the earth is made of large plates that move in different directions. They may pull apart, crash together, or rub against one another when they are moving. Most often, this movement is felt as earthquakes.

How Many Active Volcanoes Are There, and Which Is the World’s Largest?

Earth has more than 1,500 active volcanoes that we can see, most of which are located in a ring surrounding the Pacific Ocean. In America, volcanoes are located primarily in Alaska, California, Hawaii, Oregon, and Washington. However, it’s believed that around 80 percent of the world’s volcanoes are under the ocean. On the Big Island of Hawaii sits Mauna Loa, the largest active volcano in the world. It rises more than 13,000 feet above sea level and is taller than Mount Everest from its underwater base to its summit.

The Different Volcano Types

The four different volcano types are cinder cones, composite, shield, and lava volcanoes. The most simple type of volcanoes is called a cinder cone. These are oval or circular cones that are formed from cooled cinders of lava blown from a single vent. Composite volcanoes, which are also known as stratovolcanoes, are steep-sided. Mount St. Helens is a composite volcano. Shield volcanoes have a bowl-shaped center. These large volcanoes are formed by a basaltic lava flow from a central vent. The final type of volcano is formed by thick lava and is called a lava dome. The lava piles around the vent, creating a mound that grows from within.

The Differences Between Magma and Lava

Both lava and magma are liquid rock associated with volcanoes. When this molten liquid stays inside of the volcano, it is hot and called magma. When it flows from the volcano, it starts off hot and glows red and white, but the lava hardens quickly as it cools.

Volcano Flow and Formations: Pyroclastic Flow, Lahar, and Pumice

Lava isn’t the only thing to flow from the interior of a volcano when it erupts. Hot expanding gases and semi-solid fragments also race down the side of the volcano as a pyroclastic flow, and this can move as fast as a hurricane. The heat and toxic gases make it extremely deadly. A flow made up of a combination of water, debris, and pyroclastic materials is called lahar. Getting caught in a lahar can be dangerous, as it hardens when it’s no longer in motion. During volcanic explosions, an extremely porous, light-colored volcanic rock made of gas bubbles and volcanic glass is formed. This type of rock is called pumice.

The Pacific Ring of Fire

The Ring of Fire is where the majority of the world’s volcanoes on land are located. There are 452 of these volcanoes, and they circle the basin of the Pacific Ocean. The Ring of Fire is also home to roughly 90 percent of earthquake activity in the world.

Mount St. Helens

Mount St. Helens is a volcano located in the Cascade Range of Washington. It erupted on May 18, 1980, with a blast that was so loud that people who lived as far away as California and Canada heard it. This historic eruption ultimately killed 57 people and resulted in more than $1 billion in damage.

Other Notable Eruptions

In Japan, its tallest mountain, Mount Fujiyama, erupted in 1708. This eruption continued for three weeks, destroying nearby villages. In 1883, Krakatoa erupted in Indonesia with a sound so loud that it was heard in Australia. It killed 40,000 people, and for five years, it reduced global temperatures. In 1902 on the Caribbean island of Martinique, a horizontal explosion marked the eruption of Mount Pelee, which swiftly killed 30,000 people and leveled the city of Saint-Pierre to become one of the most deadly 20th century eruptions.

What Is a Tsunami?

Underwater disturbances such as volcanic eruptions or earthquakes can cause enormous waves to form. These giant sea waves are called tsunamis, and they are not only high but extremely fast and destructive. They are not tidal waves, and they are not traditional waves. Tsunamis travel in a straight path, hitting land hard like a wall of water.

Volcano-Related Vocabulary

• Magma: Molten rock that’s located inside of a volcano
• Lava: Molten rock that flows out of a volcano during an eruption
• Active Volcano: A regularly erupting volcano
• Dormant Volcano: A volcano that hasn’t erupted in years but is showing signs of activity
• Extinct Volcano: A volcano that has not erupted for thousands of years and has no signs of activity
• Geysers: Springs that expel steam and extremely hot water heated by volcanic heat into the air
• Ash: Residue or fragments of volcanic rock that’s been blasted into the air during an eruption
• Pumice: Volcanic rock formed from glass

Volcano Safety Tips

Having a plan is the best way to stay safe if a volcano should erupt. This means knowing what to do before a volcano erupts, during the eruption, and after it is over. Before the eruption, families need to create a plan. Start with building a disaster supply kit for the home and one for the family car. This should include flashlights, batteries, a battery-operated radio, face masks for dust, and protective clothing including gloves and shoes. The kit should also include bottled water, canned food, and a first aid kit to treat any injuries. Mapping out evacuation routes is another crucial part of creating a plan. There should be several routes planned and a meeting place set that is familiar to all members of the family.

During a volcano, it is important to listen to and follow evacuation orders issued by officials. Evacuate as quickly as possible to minimize getting stuck in traffic or trapped. If there are no evacuation orders or you’re stuck outdoors, find shelter as quickly as possible and take steps to protect your head and neck from any falling debris. Be cautious of mudflow, and put on long sleeves and pants for protection from hot ash that may fall. Wear goggles for eye protection and a mask for lung protection. People who are indoors should keep windows and doors closed to prevent ash from entering the building.

After the volcano is finished erupting, there will still be ash in the air, so you should stay fully covered when outdoors, including eye goggles. Families should remove any buildup of ash from the roof of their home, as it can be heavy and cause the home to collapse. And be sure to follow any instructions that the authorities give during this time.

• What Is a Volcano? (video): Click this link for a National Geographic video that talks about the Snowball Earth era and how volcanoes helped warm the planet with the greenhouse gases that they spewed.
• Volcanoes: Visit the Ready.Gov website for a brief article about what volcanoes are and what safety precautions to take if you live near a volcano.
• Fact Sheet: Volcanoes (PDF): FEMA provides a fact sheet about volcanoes that includes information on high-risk zones and how to prepare for a volcano-related emergency.
• Natural Disasters: Volcanoes: There are 1,500 known active volcanoes around the world. The European Space Agency talks about how satellites study and detect signs of volcanic activity in this article.
• How Do Volcanoes Form?: CSU Northridge explains how volcanoes form on their website.
• How Volcanoes Form: National Geographic for Kids has an article about volcanoes and the consequences of an eruption here.
• Volcano Notes: Go here to learn volcano-related terms and what they mean.
• Plate Tectonics: Click this link to see a video and an article about tectonic plates and how they relate to mountains, volcanoes, earthquakes, and more.
• What on Earth Is Plate Tectonics? (PDF): The National Park Service provides this handout with a diagram and detailed information about plate tectonics and volcanoes.
• Shield Volcanoes: The BBC provides information about and examples of shield volcanoes here.
• Composite Volcano: Visit the Kapunahala Elementary School website for pictures and information about composite volcanoes.
• Volcanoes and Lahars: The Washington State Department of Natural Resources provides information about potential volcano-related hazards, emergency response tips, and diagrams and videos about different types of volcanoes and their eruption risks.
• Lahars: Learn about the dangers associated with lahars on the Michigan Tech Department of Geological and Mining Engineering and Sciences website.
• Volcanoes (PDF): Readers who are interested in volcanoes will find useful information in this 20-page document that covers a wide variety of volcano-related topics, from the individual parts of volcanoes to the Ring of Fire and the study of volcanoes as a profession.
• Volcano: Volcanic eruptions come in many forms. An article on the Utah State Office of Education Science website explains the different types of volcanoes and what kind of eruptions that they may produce.