Which volcano is considered the most active on Earth, having been erupting continuously since 1983? This Hawaiian shield volcano has earned the nickname "the drive-up volcano" because visitors can safely approach its flowing lava. Its name in Hawaiian means "spewing" or "spreading." The ongoing eruption has added over 200 hectares (500 acres) of new land to the island of Hawaii, destroying over 700 homes in the process. Unlike explosive stratovolcanoes, it produces relatively gentle, fluid lava flows that travel slowly down its slopes. Scientists consider it the best-studied volcano in the world, with monitoring stations constantly tracking its activity. Its summit crater, Halemaʻumaʻu, is considered sacred in Hawaiian mythology as the home of the fire goddess Pele.

Which volcanic eruption in 1815 is the deadliest in recorded history, killing over 71,000 people? This Indonesian volcano, located on Sumbawa Island, produced the largest volcanic explosion in 13,000 years. The eruption was so powerful that it was heard 2,000 kilometers away (like from New York to Kansas). It ejected so much ash and sulfur dioxide into the atmosphere that global temperatures dropped by 0.4-0.7°C (0.7-1.3°F), causing 1816 to be known as the "Year Without a Summer" – crops failed across North America and Europe, leading to famine. The explosion destroyed the mountain's peak, reducing its height from 4,300 meters to 2,850 meters. The eruption column reached 43 km (27 miles) into the stratosphere.

Which Italian volcano famously buried the Roman cities of Pompeii and Herculaneum in 79 AD? This stratovolcano on the Bay of Naples is one of the most dangerous volcanoes in the world because 3 million people live within 30 kilometers (18 miles) of its crater. The 79 AD eruption was so powerful that it ejected a mushroom cloud of ash and pumice 33 km (20 miles) high. Pompeii was buried under 4-6 meters (13-20 feet) of ash, perfectly preserving buildings, artifacts, and even the shapes of human bodies (which later archaeologists filled with plaster). The volcano has erupted dozens of times since, most recently in 1944 during World War II. Its name comes from the Greek word for "son of Zeus."

Which volcano is the largest on Earth by volume and area – so massive that it is larger than the entire island of Hawaii? This Hawaiian shield volcano is the most massive mountain on Earth, with a volume of 75,000 cubic kilometers (18,000 cubic miles). Its name means "long mountain" in Hawaiian. Its summit is 4,169 meters (13,678 feet) above sea level, but its base is on the ocean floor, making its total height from base to summit over 9,000 meters (30,000 feet) – taller than Mount Everest from base to peak. It is so heavy that it has depressed the Earth's crust beneath it by 6 kilometers (4 miles). It is not currently erupting, but scientists consider it active because it has erupted several times in the last 10,000 years, most recently in 1984.

Approximately what percentage of the world's active volcanoes are located in the Pacific Ring of Fire? This horseshoe-shaped zone follows the boundaries of the Pacific Plate, where it subducts beneath other tectonic plates. The Ring stretches for 40,000 kilometers (25,000 miles) from New Zealand, up through Indonesia and Japan, across the Aleutian Islands, down the west coasts of North and South America. It is home to 452 volcanoes – about 75% of the world's total. The name was coined in 1965, and the region also produces 90% of the world's earthquakes. Countries like Japan, Indonesia, the Philippines, Chile, and the western United States are all located within this geologically active zone.

On which planet would you find Olympus Mons, the tallest volcano in the solar system at 21.9 km (13.6 miles) high? This massive shield volcano is three times taller than Mount Everest. Its base is 600 km (370 miles) wide – roughly the size of the state of Arizona. The volcano is so large that its summit lies above most of the planet's atmosphere. The volcano is considered dormant, not extinct, and is the youngest major volcano on that planet (only a few hundred million years old). Scientists believe the volcano grew so large because the planet lacks plate tectonics, allowing the same hotspot to build a single massive volcano over billions of years, unlike Earth where moving plates create chains of volcanoes like Hawaii.

Which 1883 volcanic eruption was so powerful that it destroyed 70% of the island it was on and was heard 4,800 kilometers (3,000 miles) away? This Indonesian volcano's explosion was equivalent to 200 megatons of TNT – about 13,000 times more powerful than the atomic bomb dropped on Hiroshima. The explosion completely destroyed the island of Krakatoa, leaving only a few remnants. The sound was the loudest ever recorded in human history, heard in Australia (3,500 km away) and on the island of Rodrigues near Africa (4,800 km away). The eruption generated tsunamis up to 46 meters (151 feet) high that killed over 36,000 people, washing away 165 coastal villages. The explosion created global atmospheric effects – sunsets were so red that fire departments were called out thinking there were fires.

Which Cascade Range volcano in Washington state is considered the most dangerous in the United States due to its potential for massive lahars (volcanic mudflows)? This stratovolcano erupted catastrophically on May 18, 1980, killing 57 people and reducing the mountain's height from 2,950 meters to 2,550 meters. The lateral blast was equivalent to 24 megatons of TNT (1,600 times the Hiroshima bomb). However, even more dangerous than future blasts are lahars – volcanic mudflows that could reach the 3 million people living in the Seattle-Tacoma metropolitan area. Scientists have identified evidence of massive lahars reaching Puget Sound in the past 6,000 years. The USGS continuously monitors this volcano with seismometers, GPS, and satellite imagery.

What is the name of the massive supervolcano located beneath Yellowstone National Park in Wyoming? This supervolcano has produced three supereruptions in the last 2.1 million years – 2.1 million years ago, 1.3 million years ago, and 640,000 years ago. The most recent eruption ejected 1,000 cubic kilometers (240 cubic miles) of material – 2,500 times larger than the 1980 Mount St. Helens eruption. The volcano's magma chamber is still active, powering Yellowstone's famous geysers and hot springs. A future supereruption would have devastating global effects, including a volcanic winter lasting years. However, USGS scientists say the probability of such an eruption in any given year is 1 in 730,000 – extremely low.

Which Italian volcano has been erupting almost continuously for over 2,000 years, earning it the nickname "Lighthouse of the Mediterranean"? This stratovolcano on the island of Sicily is Europe's tallest active volcano at 3,357 meters (11,014 feet) – its height changes with each eruption. The ancient Greeks believed the giant Typhon or the god Hephaestus (Vulcan to the Romans) was imprisoned beneath it, causing the eruptions. It is one of the most studied volcanoes in the world, with records of its activity dating back to 425 BCE. Despite its constant activity, it rarely causes casualties because its eruptions are usually not explosive enough to endanger the large populations living on its slopes. Its name comes from a Phoenician word meaning "furnace."