Why does a volcano erupt explosively

The tephra that fell on inhabited areas was not harmful to most people, but it was a source of irritation to those with respiratory problems and an inconvenience to the many residents with rain-water-catchment systems. For example, between about and , at least a dozen pyroclastic surges swept across the summit area. One surge erupted in killed a large number of Hawaiians traversing the summit area near the current location of HVO—these deposits can be found as far as 3.

Other explosive events resulted in ash fall at the summit and over broad areas far downwind. Unlike lava fountains, large explosive eruptionseject tephra that consists mostly of broken rock from the sides of the vent and little magma molten rock. Tephra in the eruption column reached high into the westerly jet stream wind currents and were blown downwind. Dashed line shows area covered by pyroclastic surge erupted in Solid line shows areas that may be covered by similar, future caldera eruption.

The long-term hazards will be severe when a repeat of similar explosive eruptions occur over a period of several centuries. The early part of the next explosive period will likely include a major collapse of the summit caldera that lasts days to weeks. Such a dramatic shift will be apparent to everyone, because there will be many large-magnitude earthquakes that accompany collapse of the next caldera.

There will likely be periods of years to decades between explosive eruptions. Learn more: About Volcanoes Volcano Hazards. Apply Filter. How hot is a Hawaiian volcano? Very hot!! The temperature of the lava in the tubes is about 1, degrees Celsius 2, degrees Fahrenheit. The tube system of episode 53 Pu'u O'o eruption carried lava for How dangerous are pyroclastic flows? Pyroclastic flows can be extremely destructive and deadly because of their high temperature and mobility.

For example, during the Is it dangerous to work on volcanoes? What precautions do scientists take? Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes.

For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train Will extinct volcanoes on the east coast of the U. The geologic forces that generated volcanoes in the eastern United States millions of years ago no longer exist.

Through plate tectonics, the eastern U. So new volcanic activity is not possible now or in Where is the largest active volcano in the world? Rising gradually to more than 4 km 2. Its submarine flanks descend to the sea floor an additional 5 km 3 mi , and the sea floor in turn is depressed by Mauna Loa's great mass another 8 km 5 mi.

This makes the volcano's summit about 17 km What is the difference between "magma" and "lava"? Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth's surface.

What kind of school training do you need to become a volcanologist? There are many paths to becoming a volcanologist. Most include a college or graduate school education in a scientific or technical field, but the range of specialties is very large. Training in geology, geophysics, geochemistry, biology, biochemistry, mathematics, statistics, engineering, atmospheric science, remote sensing, and related fields can What are some benefits of volcanic eruptions?

Over geologic time, volcanic eruptions and related processes have directly and indirectly benefited mankind: Volcanic materials ultimately break down and weather to form some of the most fertile soils on Earth, cultivation of which has produced abundant food and fostered civilizations. The internal heat associated with young volcanic systems has Do volcanoes affect weather? Yes, volcanoes can affect weather and the Earth's climate.

Following the eruption of Mount Pinatubo in the Philippines, cooler than normal temperatures were recorded worldwide and brilliant sunsets and sunrises were attributed to this eruption that sent fine ash and gases high into the stratosphere, forming a large volcanic cloud that How many active volcanoes are there on Earth? There are about 1, potentially active volcanoes worldwide, aside from the continuous belts of volcanoes on the ocean floor at spreading centers like the Mid-Atlantic Ridge.

About of those 1, volcanoes have erupted in historical time. Many of those are located along the Pacific Rim in what is known as the " Ring of Fire.

Can an eruption at one volcano trigger an eruption at another volcano? There are a few historic examples of simultaneous eruptions from volcanoes or volcanic vents located within about 10 kilometers 6 miles of each other, but it's difficult to Filter Total Items: Year Published: When volcanoes fall down—Catastrophic collapse and debris avalanches Despite their seeming permanence, volcanoes are prone to catastrophic collapse that can affect vast areas in a matter of minutes. Siebert, Lee; Reid, Mark E.

View Citation. Siebert, L. Geological Survey Fact Sheet , 6 p. Stovall, Wendy K. Stovall, W. Geological Survey Fact Sheet —, 6 p. Year Published: update to the U.

Geological Survey national volcanic threat assessment When erupting, all volcanoes pose a degree of risk to people and infrastructure, however, the risks are not equivalent from one volcano to another because of differences in eruptive style and geographic location. Ewert, John W. Ewert, J. Geological Survey national volcanic threat assessment: U.

Geological Survey Scientific Investigations Report —, 40 p. Year Published: U. Geological Survey Volcano Hazards Program—Assess, forecast, prepare, engage At least volcanoes in 12 States and 2 territories have erupted in the past 12, years and have the potential to erupt again. Geological Survey Fact Sheet —, 4 p. Year Published: A sight "fearfully grand": eruptions of Lassen Peak, California, to On May 22, , a large explosive eruption at the summit of Lassen Peak, California, the southernmost active volcano in the Cascade Range, devastated nearby areas and rained volcanic ash as far away as miles to the east.

Clynne, Michael A. Clynne, M. Deep within the earth as the magma resides in a magma chamber, these gases are comfortably mixed into the magma. As magma rises towards the surface, though, the gases are no longer comfortable within the melt and come out of the magma to form bubbles. In some situations, bubbles form very easily. Sometimes, though, bubbles are not able to form. When a very bubbly magma reaches the surface, the bubbles pop and send shards of magma flying in every direction as pyroclasts.

A magma without bubbles will simply ooze to the surface. In the image to the left, bubbles form deep in the conduit of the volcano and rise to the surface, fragmenting the magma. This volcano erupts explosively. If bubbles formed higher in the conduit, the magma would not fragment as much and the volcano would erupt more effusively. Bubbles control a factor known in volcanology as explosivity. The more bubbles a magma develops, the higher the explosivity of the eruption.

To better classify the size of volcanic eruptions, volcanologists developed the Volcanic Explosivity Index VEI to categorize eruptions. The VEI scale starts at 0 and has no upper limit, but the largest eruption in history was a magnitude 8.