Interior of the Earth | Class 11 Geography Notes

VOLCANOES AND VOLCANIC LANDFORMS

Volcanoes are openings in the Earth's surface through which gases, ash, and molten rock material called lava escape. A volcano is considered active if it has erupted recently or is currently erupting.

The mantle beneath the solid crust contains a weaker zone called the asthenosphere. This is the main source of magma that moves upward during volcanic eruptions. Magma is molten rock material in the upper mantle. When magma reaches the surface, it is called lava. The materials released during eruptions include lava flows, pyroclastic debris, volcanic bombs, ash, dust, and gases such as nitrogen compounds, sulfur compounds, chlorine, hydrogen, and argon.

Volcanoes are classified based on the nature of eruption and the form developed at the surface:

1. Shield Volcanoes: These are the largest volcanoes, mostly composed of basalt lava, which is very fluid when erupted. The Hawaiian volcanoes are classic examples. Shield volcanoes have gentle slopes and low explosivity unless water enters the vent, which can cause explosive eruptions. Lava moves in fountains and forms cinder cones at the vent.

2. Composite Volcanoes: Characterized by eruptions of cooler, more viscous lava than basalt. These volcanoes often have explosive eruptions, releasing large quantities of pyroclastic material and ash. The accumulation of these materials near the vent forms layered composite volcanoes.

3. Caldera: These are the most explosive volcanoes. Their eruptions are so violent that the volcano collapses on itself, forming large depressions called calderas. This indicates a huge magma chamber close to the surface.

4. Flood Basalt Provinces: These volcanoes release highly fluid lava that flows over vast areas, forming thick basalt layers. The Deccan Traps in India are a famous example, covering large parts of the Maharashtra plateau.

5. Mid-Ocean Ridge Volcanoes: Occur along mid-ocean ridges, a system of underwater mountain ranges stretching over 70,000 km across ocean basins. These ridges experience frequent volcanic eruptions.

Volcanic landforms are created by the cooling and solidification of lava either on the surface or within the Earth's crust. Cooling on the surface forms volcanic rocks, while cooling within the crust forms plutonic rocks. Intrusive forms are igneous rock bodies formed by lava cooling inside the crust, which include batholiths, lacoliths, lapoliths, phacoliths, sills, and dykes.

📊 Diagram: Figure 3.7: Shield Volcano; Figure 3.8: Cinder Cone; Figure 3.9: Composite Volcano; Figure 3.10: Volcanic Landforms

🔗 Connection: Concludes the chapter by linking Earth's interior processes to surface volcanic features and landforms.