PRESENTATION OUTLINE
Mt. Rainier
a large stratovolcano located 54 miles southeast of Seattle in the state of Washington, United States.Mt. Rainier is considered one of the most dangerous volcanoes in the world
Mount Fuji, located on Honshu Island, is the highest mountain in Japan at 12,399 ftMount Fuji lies about 100 kilometres south-west of Tokyo, and can be seen from there on a clear day
Along Destructive Plate Boundaries
Converging magma currents in the magma build up pressure at destructive plate boundaries by compressional force.
At oceanic-continental or oceanic-oceanic boundaries, the melting of the subduced plate below the subduction zone intensifies the pressure.
Cracks develop, possibly because of earthquakes, and extend downward to the magma chamber.
The magma pressure is released.
The magma rises through cracks to the earth's surface.
Along Constructive Plate Boundaries
Diverging magma currents in the magma cause two plates to drift apart from one another, leaving a gap in between.
Lava wells out of the gap to fill it, causing vulcanicity.
Note： Water pressure above the sea floor suppresses volcanic activity, so volcanic activity here is not as violent.
At Hot Spots
When lines of weakness appear in the earth crust and extend to the hot spot below, magma pressure is released.
Magma rises through the cracks to the earth's surface.
Extrusive vulcanicity occurs.
Then volcanic islands are formed (materials in round brackets are related only to the Hawaiian Islands):
Lava continuously extrudes to the earth's surface above the hot spot.
As lava cools and solidifies, volcanoes are created and grown above sea level.
Hot spots are fixed in location.
When the plate moves (e.g. the Pacific Plate moves northwest), the volcano is carried away from the hot spot.
The volcano will become extinct.
A new volcano is formed at the hot spot (e.g. at the southeast of the original volcano). A volcanic island chain (Hawaii) is formed.
At Plate Boundaries
Epicenter Diagram.svg
At destructive/constructive/conservative plate boundaries, plates move towards/move away from/slide past/ each other because of compressional/tensional/lateral force.
Magma is composed of molten rock and is stored in the Earth's crust. Lava is magma that reaches the surface of our planet through a volcano vent.
Active,inactive
Those definitions are not set in stone, and they mean different things to different people and to different volcanoes. One of the simpler ways to answer is that an active volcano is one that has erupted since the last ice age (i.e., in the past ~10,000 years). That is the definition of active used by the Global Volcanism Program in their catalogs. A dormant volcano would then be one that hasn’t erupted in the past 10,000 years, but which is expected to erupt again. An extinct volcano would be one that nobody expects to ever erupt again. These are human definitions of natural things – there have been a number of eruptions from “extinct” volcanoes!
