VOLCANIC LANDFORM: EXTRUSIVE AND INTRUSIVE

Volcanic landforms are the result of volcanic activity, which can occur both above and below the Earth’s surface. These landforms are broadly classified into two categories: extrusive and intrusive, based on whether the magma reaches the Earth’s surface or solidifies beneath it.

1. Extrusive Volcanic Landforms

Extrusive landforms are created when magma erupts onto the Earth’s surface and solidifies. They often exhibit characteristic features such as lava flows, ash deposits, and volcanic cones.

a. Lava Flows

1. Basalt Plateaus:
   • Description: Extensive, flat areas covered with layers of basaltic lava flows.
   • Example: Columbia River Basalt Group in the Pacific Northwest, USA.
2. Lava Fields:
   • Description: Large areas covered by hardened lava flows.
   • Example: Holuhraun Lava Field in Iceland, formed during the 2014–2015 eruption of Bardarbunga volcano.

b. Volcanic Cones

1. Shield Volcanoes:
   • Description: Broad, gently sloping volcanoes with shallow slopes formed by the accumulation of basaltic lava flows.
   • Example: Mauna Loa and Mauna Kea in Hawaii.
2. Stratovolcanoes (Composite Volcanoes):
   • Description: Steep-sided, symmetrical volcanoes built up by alternating layers of lava flows, volcanic ash, and other volcanic debris.
   • Example: Mount Fuji in Japan, Mount Vesuvius in Italy.
3. Cinder Cones:
   • Description: Small, steep-sided volcanoes formed from the accumulation of volcanic debris around a vent.
   • Example: Parícutin in Mexico, Sunset Crater in Arizona, USA.

c. Volcanic Deposits

1. Pyroclastic Deposits:
   • Description: Deposits of volcanic ash, lapilli (small rock fragments), and volcanic bombs ejected during explosive eruptions.
   • Example: The Bishop Tuff in California, USA, formed during the eruption of the Long Valley Caldera.
2. Volcanic Ash Layers:
   • Description: Layers of fine volcanic ash deposited over large areas.
   • Example: The ash deposits from the 1991 eruption of Mount Pinatubo in the Philippines, which blanketed surrounding regions.

2. Intrusive Volcanic Landforms

Intrusive landforms are created when magma solidifies beneath the Earth’s surface, forming various structures as it cools and crystallizes.

a. Plutons

1. Batholiths:
   • Description: Large, irregular-shaped intrusive bodies composed of coarsely crystalline igneous rocks.
   • Example: Sierra Nevada Batholith in California, USA.
2. Stocks:
   • Description: Smaller plutons, similar to batholiths but with surface exposure less than 100 square kilometers.
   • Example: El Capitan in Yosemite National Park, California, USA.
3. Laccoliths:
   • Description: Intrusions that form domelike structures with flat bottoms and arched roofs.
   • Example: Henry Mountains in Utah, USA.

b. Dykes and Sills

1. Dykes:
   • Description: Tabular intrusions that cut across existing rock layers.
   • Example: Palisades Sill in New Jersey and New York, USA.
2. Sills:
   • Description: Tabular intrusions that parallel the existing rock layers.
   • Example: Whin Sill in England, UK.

c. Volcanic Necks and Pipes

1. Volcanic Necks:
   • Description: Solidified remains of volcanic conduits or vents that have been exposed by erosion.
   • Example: Shiprock in New Mexico, USA.
2. Volcanic Pipes:
   • Description: Narrow, vertical conduits connecting a magma chamber to the surface.
   • Example: Kimberlite pipes, which often contain diamonds, such as the Kimberley Diamond Mine in South Africa.

Conclusion

Extrusive and intrusive volcanic landforms offer insights into the diverse range of geological processes associated with volcanic activity. Extrusive landforms, including lava flows, volcanic cones, and volcanic deposits, are formed on the Earth’s surface during eruptions. Intrusive landforms, such as plutons, dykes, and sills, are formed beneath the surface as magma cools and solidifies. Understanding these landforms and their associated features provides valuable information about past volcanic activity and the geological history of regions around the world.