Shield volcano with a cinder cone
Kilauea has been erupting almost constantly from its eastern rift zone since 1983. Finally in April 2018, the volcanic cone known as Puʻu ʻŌʻō (pronounced ‘po-oo-OH-oh’) stopped erupting as its crater floor collapsed. After 90 days or so of no activity, scientists could be confident its 35-year-long eruption had ended. While the eruption of Puʻu ʻŌʻō may be over, Kīlauea is still an active volcano and new eruptions are likely to happen in the future.
On May 4, 2018, an earthquake with a magnitude of 6.9 struck Hawaii island. The earthquake's epicenter was near the south flank of Kīlauea. Most earthquakes that are directly beneath a volcano are caused by magma exerting pressure on the rocks until they crack.
Composite volcano with cinder cones, caldera
Composite volcano with caldera
A relatively young volcano, Vesuvius formed probably fewer than 200,000 years ago when the African and Eurasian plates collided in a subduction zone. The volcano was dormant for centuries.
Vesuvius last erupted in 1944. Today more than two million people live on and around Vesuvius. It is still considered a dangerous and potentially deadly volcano. The authorities offer to pay for people to move out of the eruption “red zone”.
Composite volcano with lava dome
On May 18, 1980, U.S. Geological Survey (USGS) scientist David Johnston was camping at an observation post near Mount St. Helens. From a base of operations in Vancouver, Washington, the USGS was monitoring the volcano, aware of the danger for a large eruption.
At 8:32 a.m., Johnston radioed the base: "Vancouver, Vancouver, this is it!"
The picturesque Cascade Range peak had erupted. The violent blast killed Johnston and 56 other people and tore off nearly 400 meters (1,300 feet) of the volcano's top. More than 600 square kilometers (230 square miles) of surrounding forest were devastated.
Volcanologists weren't surprised. The volcano, less than about 37,000 years old, had been especially active over the last 4,000 years. Eruptions, usually explosive, had occurred at a rate of about one every hundred years. Before 1980, the last eruption happened 130 years previously, and scientists were alert for the explosion.
A few months before the May eruption, a series of earthquakes began to shake the volcano. Several small steam eruptions occurred, new fissures appeared, and a bulge developed on the north flank of the volcano.
The bulge got larger and larger. A week before the big eruption, it was expanding at a rate of about two meters (seven feet) per day.
When the big blast occurred, the entire northern slope of the volcano above the bulge slid downward. The huge landslide sparked a hydrothermal blast that swept through the surrounding forests, snapping trees like twigs.
In addition, a column of volcanic rock and lava fragments rose from the volcano's summit to a height of 20 kilometers (12 miles). The eruption lasted nine hours and spread debris as far as the Great Plains.
The eruption destroyed the volcano's peak, replacing it with a horseshoe-shaped crater. Since the 1980 blast smaller eruptions have built a lava dome over the vent.
Between 2004 and 2005 Mount St. Helens gave out steam and ash. Until 2008 it continuously gave out three years of semi-solid lava. It is likely that Mount St. Helens will erupt again. However, an eruption like the one in 1980 is unlikely now that a deep crater has formed.
Composite volcano with lava domes
Underneath Montserrat, the North and South American plates push beneath the Caribbean plate in a subduction zone. From this tectonic activity rose Soufriere Hills, a stratovolcano on the southern end of the island.
Soufriere Hills continues to throw ash and stone periodically across the southern part of the island.