Geologists anxiously watched the Kilauea volcano on Hawaii's Big Island in May 2018 as it vented toxic steam and released lava. They warned that if the volcano explodes, it will have the power to hurl boulders the size of refrigerators.
Many volcanoes around the world have such deadly potential, even if they happen to be quieter at the moment. Here is a look at some other volcanoes that could cause great damage and harm.
Mayon is the most active volcano in the Philippines. It has erupted almost 50 times in the past 500 years.
Mayon's most recent eruption
The volcano most recently erupted in January 2018, pictured here.
Nevado del Ruiz
Nevado del Ruiz, in Colombia, might not have huge eruptions, but its smaller eruptions are known to trigger destructive and deadly mudflows.
Nevado del Ruiz: Killer of thousands
In 1985, a mudflow caused by an eruption killed more than 23,000 people.
Here, two survivors walk down a dirt road on Nov. 15, 1985, near Armero, Colombia.
Popocatepetl is the most active volcano in Mexico, having erupted 15 times since the 1500s.
Popocatepetl means "Smoking Mountain" in the Aztec language.
Here, ash spews from the volcano in 2013.
Popocatépetl: Most recent eruption
The volcano most recently erupted in November 2017, pictured here.
The Katla volcano, which is covered by an ice cap in Iceland, is a very active volcano that is known to erupt at least every 100 years.
If or when it erupts again, major flooding and lava flow could cause massive destruction.
Katla: Recent activity
The volcano's last major eruption was in 1918, but it's shown additional activity since 1999. Tremors were detected under Katla in August 2016.
Cumbre Vieja volcano
Cumbre Vieja, in the Canary Islands of Spain, is currently dormant, but it's still an active volcano.
Scientists predict that a major eruption could cause the volcano's west flank to fail, which could result in a devastating mega-tsunami.
Cumbre Vieja: Lava maker
The volcano has erupted twice in recent history — once in 1949 and once in 1971.
During the first eruption, an estimated 60 million cubic meters of lava exploded from the volcano.
Mount Vesuvius, in Campania, Italy, is considered one of the most dangerous volcanoes in the world. It is prone to violent eruptions, and about 3 million people live nearby.
Mount Vesuvius: A famous eruption
Mount Vesuvius is best known for its eruption in A.D. 79, which buried the Roman cities of Pompeii and Herculaneum.
Mount Unzen is an active group of stratovolcanoes in Japan.
In 1792, one of its lava domes collapsed, triggering a mega-tsunami that killed more than 14,000 people in Japan's worst-ever volcanic disaster.
Mount Unzen: Active in the '90s
The volcano had a very active period between 1990 and 1995. An eruption in 1991 killed 43 people.
Here, vehicles sit submerged in mud in a flooded residential area at the foot of the volcanic mountain.
The Krakatoa volcano, in the Indonesian province of Lampung, most recently erupted in 2008, and people are warned to stay about 2 miles away from it at all times.
The Volcanological Survey of Indonesia raised the eruption alert status of Anak Krakatau to Level III in 2009.
Krakatoa: Historic eruption
The 1883 eruption of the volcano was one of the deadliest and most powerful eruptions in recorded history. An estimated 36,000 people were killed as a result of thermal injury from the blasts and many more died in tsunamis triggered by the eruption.
Mauna Loa volcano
Mauna Loa, in Hawaii, is an extremely active volcano that's erupted 33 times since 1843, according to the U.S. Geological Survey.
Mauna Loa: City of lava
Mauna Loa most recently erupted in 1984. The city of Hilo, Hawaii is partly built on the volcano's lava flows from decades past.
Mount Merapi, on the border between Central Java and Yogyakarta, Indonesia, has already erupted several times, causing destruction and casualties.
Merapi literally means "the one making fire."
Mount Merapi: Flying rock fragments
The volcano last erupted in 2010.
Here, motorists ride as pyroclastic material from Mount Merapi billows in the background.
Mount St. Helens
Mount St. Helens, an active volcano in Skamania County, Washington, is responsible for the deadliest and most economically destructive volcanic activity in the United States.
Mount St. Helens: 1980 disaster
In 1980, the volcano erupted, killing 57 people and devastating the area.
Here, Mount St. Helens sends a plume of ash, smoke and debris skyward in a violent eruption.
Mount Rainier, in Washington state, is considered one of the most dangerous volcanoes in the world; if it erupts, it could blast massive amounts of ash into the atmosphere.
Mount Rainier: Ash hazard
The volcano erupted most recently in the 1800s.