Can lakes near volcanoes become acidic enough to be dangerous to people and animals?

Yes. Crater lakes atop volcanoes are typically the most acid, with pH values as low as 0.1 (very strong acid). Normal lake waters, in contrast, have relatively neutral pH values near 7.0.

The crater lake at El Chichon volcano in Mexico had a pH of 0.5 in 1983 and Mount Pinatubo's crater lake had a pH of 1.9 in 1992. The acid waters of these lakes are capable of causing burns to human skin but are unlikely to dissolve metal quickly. Gases from magma that dissolve in lake water to form such acidic brews include carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen chloride, and hydrogen fluoride.

Acidic lakes that are capable of dissolving an aluminum boat in a matter of minutes (as seen in movies) are not realistic.

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Do earthquakes large enough to collapse buildings and roads accompany volcanic eruptions?

Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy buildings and roads. The largest earthquakes at Mount St. Helens in 1980 were magnitude 5, large enough to sway trees and damage buildings, but not destroy them. During the huge eruption of Mount Pinatubo in...

Can volcanic eruptions endanger helicopters and other aircraft?

Yes. Encounters between aircraft and clouds of volcanic ash are a serious concern. Jet engines and other aircraft components are vulnerable to damage by fine, abrasive volcanic ash, which can drift in dangerous concentrations hundreds of miles downwind from an erupting volcano. In the past, many aircraft have accidentally encountered volcanic ash...

What was the largest volcanic eruption in the 20th century?

The world's largest eruption of the 20th century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6th. This volume is equivalent to 230 years of eruption at Kilauea (Hawaii) or about 30 times the volume erupted by Mount St. Helens (Washington...

Will extinct volcanoes on the east coast of the U.S. erupt again?

No. The geologic forces that generated volcanoes in the eastern United States millions of years ago no longer exist. Through plate tectonics, the eastern U.S. has been isolated from the global tectonic features (tectonic plate boundaries and hot spots in the mantle), that cause volcanic activity. 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 (2.5 mi) above sea level, Hawaii’s Mauna Loa is the largest active volcano on our planet. 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 (10.5 mi) above its...

What was the most destructive volcanic eruption in the history of the United States?

The May 18, 1980 eruption of Mount St. Helens (Washington) was the most destructive in the history of the United States. Novarupta (Katmai) Volcano in Alaska erupted considerably more material in 1912, but owing to the isolation and sparse population of the region, there were no human deaths and little property damage. In contrast, the eruption of...

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 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...

Can an eruption at one volcano trigger an eruption at another volcano?

There is no definitive evidence that an eruption at one volcano can trigger an eruption at a volcano that’s hundreds of kilometers/miles away or on a different continent. 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...

Do volcanoes affect weather?

Yes, volcanoes can affect weather and the Earth's climate . Following the 1991 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 1,350 potentially active volcanoes worldwide, aside from the continuous belts of volcanoes on the ocean floor at spreading centers like the Mid-Atlantic Ridge . About 500 of those 1,350 volcanoes have erupted in historical time. Many of those are located along the Pacific Rim in what is known as the " Ring of Fire ." In the United...
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Fumarole on Kīlauea Volcano, Hawaiʻi. Elemental sulfur vapor escaping from the fumarole has cooled to form yellow-colored crysta
April 14, 2016

Fumarole on Kīlauea Volcano, Hawaiʻi

Fumarole on Kīlauea Volcano, Hawaiʻi. Elemental sulfur vapor escaping from the fumarole has cooled to form yellow-colored crystals around its margins. Credit: Robert L. Christiansen.

Image: Sampling Acid Mine Drainage in Elk_County, PA
November 6, 2007

Sampling Acid Mine Drainage in Elk_County, PA

Sampling acid mine drainage residuals in Elk County, Pennsylvania.  The USGS has pioneered a new use for these residuals that are currently a disposal challenge, using them to filter phosphorus from agricultural and municipal wastewaters.

Attribution: Water Resources
Image: Lake Tyrrel. Acid Lake
September 20, 2007

Lake Tyrrel. Acid Lake

Jim Crowley (USGS), Jeff Kargel (University of Arizona. Studying Earth as a Mars analog.

Image: Lake Chandler. Acid Lake
September 18, 2007

Lake Chandler. Acid Lake

Jim Crowley (USGS) measuring pH in the acid lake Chandler in Australia.

Image: Green Lake. Acid Lake
September 17, 2007

Green Lake. Acid Lake

Jim Crowley (USGS), Nathan Bridges (JPL). Field trip to Australia to study acid lakes as Mars analogs.

Image: Davis Rd. Carbon Dioxide Vent
December 25, 2004

Davis Rd. Carbon Dioxide Vent

Davis Rd. carbon dioxide vent, Salton Sea, California.

Image: Measuring a Superheated Fumarole
September 30, 1998

Measuring a Superheated Fumarole

USGS geochemist Bill Evans measures the temperature of a superheated (hotter than the boiling point) fumarole in Lassen Volcanic National Park.

Large umbrella shaped cloud of volcanic ash viewed from a distance
June 15, 1991

Giant ash cloud from the eruption of Mount Pinatubo, 1991

Giant ash cloud from the eruption of Mount Pinatubo, 1991 towering above farms and agricultural lands in the Philippines.

Image: Sampling a Fumarole
July 31, 1990

Sampling a Fumarole

USGS geochemist Cathy Janik (left) and Iceland Geosurvey chemist Jón Örn Bjarnason (right) collect a gas sample from a fumarole in Lassen Volcanic National Park.

Image: CO2 Hazard Area sign

CO2 Hazard Area sign

CO2 Hazard sign at Horseshoe Lake.

Attribution: Natural Hazards
Image: Natural Iron-rich Acidic Spring Flowing into Cement Creek

Natural Iron-rich Acidic Spring Flowing into Cement Creek

Photograph showing natural iron-rich acidic spring flowing into Cement Creek near Silverton, Colorado.  Similar natural springs contribute water to Cement Creek and other tributaries of the upper Animas River.