- Volcanoes are openings in the crust of the earth that allow hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
- The word "volcano" comes from "Vulcan", the god of fire in Roman mythology.
- Volcanoes are usually found where some of the earth's tectonic plates are diverging or converging, mostly underwater.
- Large volcano eruptions affect temperature, obscure the sun with ash and sulfuric acid, while also cooling the Earth's lower atmosphere.
- Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.
- A popular way of classifying magmatic volcanoes is by their frequency of eruption: active (regular activity), dormant (recent historical activity but now quiet) or extinct (no activity in historical times and unlikely to erupt again). However, scientists are more likely to describe them by others characteristics, such as their shape, how they formed or how they erupt.
- Some of the Earth's most "active" volcanoes include the Kīlauea, Mount Etna and the Mount Yasur, in Vanuatu, which has been erupting almost continuously for about 800 years.
- About 500 million people live near active volcanoes around the world.
- While many Volcanoes have summit craters, others have rugged peaks formed by lava domes or even massive plateaus.
- The molten rock expelled through an eruption, at temperatures from 1,292 to 2,192 °F (700 to 1,200 °C), is called lava.
- Water vapor is the most abundant volcanic gas, along with sulfur dioxide and carbon dioxide.
- The 1815 eruption of Mount Tambora, in Indonesia, was the largest in recorded human history. It created such global climate anomalies that 1816 became known as the "Year Without a Summer". Agricultural crops failed and livestock died resulting in one of the worst famines of the century.
- The Permian–Triassic mass extinction, 252 million years ago, might have been caused by massive volcanic eruptions.
On April 1, 1974, black smoke was seen rising from Mount Edgecumbe, a volcano in Alaska. When a Coast Guard pilot came closer to investigate, he found 70 tires burning and the words "APRIL FOOL" spray painted into the snow.
The volcanic system beneath Yellowstone holds