volcano
Volcanoes are global phenomena, occurring not only on Earth but also on other celestial bodies within the Solar System, particularly on Earth-like planets, where they are considered a common feature. Undoubtedly, volcanic activity also takes place across the cosmos. The lunar surface is largely covered with volcanic rocks, while the most prominent elevations on Mars have been constructed by massive volcanic edifices.
Volcanoes generally occur in regions where lithospheric plates converge or diverge. Structurally, every volcano consists of three main parts:
1. Crater – the summit opening of the volcano.
2. Magma chamber – the reservoir where molten material accumulates prior to eruption.
3. Central conduit – the passage that connects the magma chamber to the crater.
The six principal volcanoes of Iran, some of which are dormant, include:
1. Damavand Volcano
2. Sahand Volcano
3. Sabalan Volcano
4. Taftan Volcano
5. Bazman Volcano
6. Ararat Volcano
Tectonic Setting | Formation Location | Magma Formation Mechanism | Type of Magma | Type of Eruption | Representative Examples |
(Divergent) | Continental and Mid-Oceanic Rifts | (Decompression melting) | Basaltic (Mafic) | Quiet, Fluid | Iceland, Mid-Atlantic |
(Convergent/Subduction) | Subduction Zones (Oceanic-Oceanic or Oceanic-Continental) | Addition of Water and Volatiles to the Mantle and Lowering of Melting Temperature | Andesitic to Rhyolitic | Explosive, Intense | Pacific Ring of Fire, Andes Mountains, Japan |
(Continental Arc) | Along Continental Subduction Boundaries | Similar to above, but with Continental Composition | More Siliceous, More Viscous | Plinian eruptions | Andes, Cascades (North America) |
(Island Arc) | In Seas and Oceans | Melting Induced by Subduction of an Oceanic Plate | Andesitic | Explosive | Philippines, Japan |
(Oceanic Hotspots) | Within Oceanic Plates, Away from Boundaries | (Mantle plume) | Basaltic | Quiet, Fluid | Hawaii |
(Continental Hotspots) | Within Continents | Mantle Plume | Rhyolitic (Siliceous, Highly Viscous) | Super-Explosive | Yellowstone (USA) |
(Continental Rift) | Continental Extensional Regions | Pressure Reduction Due to Crustal Extension | Basaltic to Rhyolitic | Mixed (Effusive + Explosive) | East African Rift |
The volcano model in the Earth Science Museum represents Subduction Zone Volcanoes.
Definition of Subduction Zone:
A subduction zone is where one tectonic plate (usually oceanic) sinks beneath another plate (continental or oceanic). This process creates a deep ocean trench and specific geological activities.
How volcanoes form:
- When an oceanic plate subducts beneath a continental plate, with increasing depth, water and volatile materials are released from the subducting rocks.
- This water lowers the melting point of mantle rocks, causing partial melting and the formation of magma.
- Since magma is less dense than the surrounding rocks, it rises toward the surface and eventually leads to the formation of subduction zone volcanoes.
Characteristics of subduction zone volcanoes:
- They are usually explosive and arc-shaped.
- Their magma ranges from basalt to andesite and contains high amounts of silica and gases.
- Famous example: The volcanoes of the Pacific "Ring of Fire."
Geological importance:
- These volcanoes are important sources of metallic elements and minerals.
- Their activity can trigger earthquakes and tsunamis.
Volcanoes at subduction zone boundaries are distributed across various regions of the world, most notably around the Pacific Ocean in the so-called "Ring of Fire." These regions, due to the collision of tectonic plates and the subduction of one beneath another, are characterized by intense volcanic and seismic activity.
