volcanology
30 questions tagged volcanology — spanning every one of the seven Ws.
What Is a Fumarole?
A fumarole is a vent in the Earth's surface that emits steam and volcanic gases from underground magma.
Why do subduction zones create volcanic arcs?
Subduction zones create volcanic arcs because a sinking oceanic plate releases water into the mantle, lowering the melting point of rock. That melt rises and forms volcanoes on the overriding plate.
Why do hotspots create chains of volcanoes?
Hotspots create chains because the tectonic plate moves over a long-lived source of magma, while the magma source stays roughly in place. Older volcanoes move away and become inactive as new ones form above the hotspot.
Why are shield volcanoes so broad and gently sloped?
Shield volcanoes are broad because they erupt low-viscosity basaltic lava that flows far before cooling. Over many eruptions, those thin layers build a wide, gently sloping shape.
What is pumice?
Pumice is a light, porous volcanic rock filled with gas bubbles. So many bubbles can be trapped in it that some pieces float on water.
What is obsidian?
Obsidian is volcanic glass formed when lava cools so rapidly that crystals do not have time to grow. It is usually dark and breaks with a sharp, glassy fracture.
What is pillow lava?
Pillow lava is basaltic lava that cools underwater into rounded, pillow-shaped masses. The outer skin hardens quickly while the inside keeps flowing.
What is volcanic ash?
Volcanic ash is made of tiny fragments of rock, glass, and minerals blasted out during an eruption. Despite its name, it is not the same as the ash from a fire.
When was the Yellowstone supervolcano caldera recognized?
In the 1960s and 1970s, when geologists identified the Yellowstone caldera as the product of huge ancient eruptions.
Which volcano has the longest known lava tube?
The Kazumura Cave lava tube on Hawaii’s Kilauea is one of the world’s longest known lava tubes, extending more than 65 km.
Whose idea first explained hotspot volcanism?
John Tuzo Wilson is closely associated with the hotspot concept and volcanic chains like Hawaii. The idea explains volcanoes that form away from plate boundaries.
Whose measurements first showed that some volcanic ash layers can be traced worldwide?
Vincent E. Morgan and others helped develop tephrochronology, but Surtsey-style modern volcanology was advanced especially by Sigurdur Thorarinsson in Iceland. He showed that ash layers can be matched across large areas.
How does a volcano change the landscape after an eruption?
Volcanic eruptions can build new land, bury terrain in ash and lava, and reshape valleys and coastlines. They can also leave behind fertile soil once the material weathers.
Why are some volcanoes eruptive while others mostly ooze lava?
Volcanoes erupt explosively when gas-rich, viscous magma traps pressure; runny basaltic magma lets gas escape more easily and tends to flow instead. The key differences are magma composition, temperature, and dissolved gas content.
Where is the Ring of Fire found around the Pacific Ocean?
The Ring of Fire circles much of the Pacific Ocean basin. It is a belt of frequent earthquakes and volcanoes along plate boundaries.
Which is the largest active volcano on Earth?
Mauna Loa in Hawaii is the largest active volcano on Earth by volume and area covered. It rises about 9 km from its oceanic base to summit, though much of it is below sea level.
Which country has the greatest number of volcanoes?
Indonesia is widely recognized as the country with the greatest number of volcanoes. It has more than 100 active volcanoes and many more dormant or extinct ones.
Whose name is attached to the scale used to describe volcanic explosivity?
Chris Newhall and Stephen Self developed the Volcanic Explosivity Index in 1982. The VEI ranks eruptions from 0 to 8.
How do scientists tell when a volcano erupted long ago?
They date ash layers, lava flows, and minerals with radiometric methods, then match them to layers in the geologic record.
Why do some volcanic eruptions produce pumice that can float on water?
Pumice forms when gas-rich magma cools so quickly that bubbles get trapped inside, making the rock extremely porous and light. Some pumice is less dense than water because it can be mostly empty space.
Why do some volcanoes have steep, explosive cones while others spread out as broad, gentle slopes?
The shape mostly depends on magma thickness and gas content. Runny basaltic lava makes broad shield volcanoes, while sticky, silica-rich magma traps gas and builds steep composite volcanoes.
Why do lava tubes form under some volcanic flows?
The surface of a lava flow cools and hardens first, while molten lava keeps moving underneath. If the eruption continues long enough, it can drain out and leave a tunnel behind.
What is tephra?
Tephra is the general term for volcanic material blasted into the air during an eruption. It includes ash, lapilli and volcanic bombs or blocks.
When was the first volcanic eruption scientifically described in detail?
One famous detailed account was published after the 79 CE eruption of Mount Vesuvius by Pliny the Younger.
When was the first magma chamber model proposed?
Concepts of magma chambers developed in the late 19th and early 20th centuries as volcanology advanced.
Where is Yellowstone’s supervolcano located?
It is under Yellowstone National Park in the United States, mainly in northwestern Wyoming. The volcanic system also extends into Montana and Idaho.
Where is Dallol located?
Dallol is in Ethiopia’s Afar Depression, near the border with Eritrea. It is known for its colorful hydrothermal features and extreme heat.
Where is the Siberian Traps volcanic province located?
It is in Siberia, Russia, especially around the area of the Tunguska and Yenisei basins. It formed one of the largest volcanic events in Earth history.
How do volcanoes create new land on the ocean floor at mid-ocean ridges?
Magma rises where tectonic plates pull apart, then cools into basaltic crust. Over time, repeated eruptions build long underwater mountain chains and new seafloor.
How do volcanoes affect climate after a major eruption?
Big explosive eruptions can inject sulfur compounds into the stratosphere, where they form reflective particles that cool Earth for a few years.