Mount St. Helens shortly after the eruption of May 18, 1980

Mount St. Helens shortly after the eruption of May 18, 1980





Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Confusion however, can arise because many volcanoes which scientists consider to be active are referred to as dormant by laypersons or in the media.



Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct.



For example, the Yellowstone Caldera in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

EPA to Mandate Reductions in Emissions from Volcanoes

Emission from volcanoes in the future could be greatly restricted under new rules that are part of the Clean Air Planning Act.
(Mt. St. Helens, Washington State) Under new rules that are part of the Clean Air Planning Act, volcanoes, long responsible for more particulate and sulfur dioxide pollution than all human-caused emissions, might not get a pass any longer.

The volcanic emissions portions of the legislation was finally agreed upon by congressional negotiators after congress decided to allow states in which eruptions occur to come up with their own enforcement mechanisms.

"We realize that it might be difficult for the states to come up with efficient and cost-effective measures for achieving volcanic emission reductions", said EPA Assistant Administrator Dr. Susan Vulcan. "That is why the reduction requirements are implemented gradually over time...only 5% each year".

Dr. Vulcan said that state officials will have a much easier time than some countries will have if the United Nations Volcanic Emissions Negation Treaty (UN-VENT) is ratified. She explained that volcanoes in the United States are not nearly as explosive as volcanoes in other countries. For instance, the eruption of Mt. Pinatubo in the Phillipines in June of 1991 emitted millions of tons of sulfur, a pollution event that is well beyond what can be cleansed by scrubber technology now widely used at coal-fired power plants.

VOLCANO AND LAND FORMS

Volcanoes create an almost infinite variety of landforms and terrain. However, geologists have noticed patterns when studying these different terrains, that allow them to group them into categories, based on how they are the same, and how they are different. These four landform types are called lava flows, volcanic peaks, calderas, and volcanic necks.

MAIN FEATURES OF VOLCANO

VOLCANIC INJECTION

There are many different kinds of volcanic activity and eruptions: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.

Cross-section through a stratovolcano

Cross-section through a stratovolcano (vertical scale is exaggerated):
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Branch pipe
7. Layers of ash emitted by the volcano
8. Flank 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15. Ash cloud

It takes a savvy gutsy photographer to take night photos like this one where hot gases in a molten lava pool creates explosive imagery! The lava photos in this section were taken by John Alexander and used with his permission.