- A volcanic arc is a chain of volcanoes.
- Positioned in an arc shape.
- Offshore volcanoes resulting in a volcanic island arc.
- They result;
-Subduction of an oceanic tectonic plate under another tectonic plate.
-Often parallel an oceanic trench.
- The oceanic plate is saturated with water.
- It volatiles water drastically lower the melting point of the mantle.
- Pressure squeezes water out of the plate.
- It comes to the mantle.
- After melting mantle ,forms magma at depth under the over riding plate.
- The magma ascends to form an arc of volcanoes parallel to the subduction zone.
- The Hawaiian Islands hotspot chain,
The older islands (tens of millions of years)
Which is more rocky.
- Volcanic arcs do not generally exhibit simple age pattern.
- There are two types of volcanic arcs:
1.Oceanic Arcs
- Formed oceanic crust.
- Subducts beneath other oceanic crust.
- On an adjacent plate.
- Creating a volcanic island arc.
- Not all island arcs are volcanic island arcs.
e.g.Mariana Islands ,western Pacific Ocean
Lesser Antilles,western Atlantic Ocean.
Cascade Volcanic Arc,western North America
Andes,western edge of South America
2.Continental Arcs
- Form oceanic crust.
- Subducts beneath continental crust.
- On an adjacent plate.
- Creating an arc-shaped mountain belt.
- Not all mountain belts are formed this way.
e.g.
- Cascade Volcanic Arc
- Alaska Peninsula
- Aleutian Range
- Kamchatka
- AndesNorth Volcanic Zone
- Central Volcanic Zone
- South Volcanic Zone
- Austral Volcanic Zone
- Central America Volcanic Arc
- There are isolated.
- Most volcanoes in a mountain belt.
- Vesuvius & Etna , Italy part of separate.
- Different kinds of mountainous volcanic ensembles.
No comments:
Post a Comment