Volcanism and Volcanicity
Volcanism and volcanicity are fundamental topics in the study of physical geography, crucial for UPSC Exam. This page offers an in-depth exploration of these phenomena, shedding light on the processes that lead to volcanic activity and the various forms it can take.
- A volcano on Earth is a vent or fissure in the crust through which lava, ash, rock and gases erupt.
- Sometimes they can be preceded by emissions of steam and gas from small vents in the ground.
- Nuée ardente, or pyroclastic flow is a fluidized mixture of hot gas and incandescent particles that sweeps down a volcano’s flanks, incinerating everything in its path.
VOLCANO ANATOMY
When volcanoes erupt, magma moves upward from a magma chamber and into a vent or conduit. It flows out from a crater at the top, or sometimes emerges at a secondary site on the side of the volcano resulting in a flank eruption.
Erupted materials accumulate around the vent forming a volcanic mountain. The accumulated material might consist of layers of solidified lava, called lava flows, but it might also include fragments of various sizes that have been thrown from the volcano.
MECHANISM & CAUSES OF VULCANISM
Mechanism of volcanism is closely associated with several interconnected processes.
- Average increase of temperature with increasing depth at the rate of 25-32 degree Celsius per km.
- Origin of magma due to lowering of melting point caused by reduction in the pressure of overlying super incumbent load.
- Origin of gases and vapour due to heating of water which reaches underground through percolation.
- Ascent of magma forced by enormous volume of gases and vapour.
- Occurrence of volcanic eruptions.
WHY NO VOLCANOES IN HIMALAYAS?
- Not much rise of temperature as the subduction angle is not much due to C-C type convergence.
- Absence of oceanic plate has not allowed much water to be heated up and form vapours.
- Double layering has increased crustal thickness which do not allow magma to outpour in the form of lava.
GLOBAL DISTRIBUTION OF VOLCANOES
PLATE TECTONICS AND VOLCANISM
- Stratovolcanoes tend to form at subduction zones, or convergent plate margins, where an oceanic plate slides beneath a continental plate and contributes to the rise of magma to the surface.
- At rift zones, or divergent margins, shield volcanoes tend to form as two oceanic plates pull slowly apart and magma effuses upward through the gap.
- Volcanoes are not generally found at strike-slip zones, where two plates slide laterally past each other.
- “Hot spot” volcanoes may form where plumes of lava rise from deep within the mantle to Earth’s crust far from any plate margins.
EFFECT OF VOLCANOS ON CLIMATE
Cooling effect:
- Volcanic ash or dust released into the atmosphere during an eruption shade sunlight and cause temporary cooling.
- Smallest particles of dust get into the stratosphere and can stay in the stratosphere for months, blocking sunlight and causing cooling over large areas of the Earth.
- Volcanoes emit sulphur dioxide which combines with water to form sulfuric acid aerosols. This in turn makes a haze of tiny droplets in the stratosphere that reflects incoming solar radiation, causing cooling of the Earth’s surface.
- Ex. According to studies, Pinatubo spewed about 15 million tonnes of sulphur dioxide into stratosphere. The total mass of SO2 in the volcanic cloud was 20 Tg. Researchers recorded 0.5 degrees Celsius (°C) drop in the average global temperature over large parts of the earth between 1992 and 1993.
Warming effect:
- Volcanoes also release large amounts of greenhouse gases such as water vapor and carbon dioxide.
- There have been times during Earth history when intense volcanism has significantly increased global warming.
Ozone layer depletion:
- Sulphate aerosols can deplete ozone layer too.
HOT WATER SPRINGS IN INDIA
Thermal springs or hot water springs are formed due to geothermally heated water emerging onto the earth’s surface through cracks. This heat comes from deep inside the earth’s surface. The heat produced is either through the magma within the Earth’s crust or through the movement of fault in the crust. The heated water being less dense, rises upwards. The Geological Survey of India (GSI) have identified more than 340 hot spring locations.
SIGNIFICANCE
- High geothermal energy potential
- Presence of warm water provide relief to people living in colder areas.
- Host communities of microorganisms like extremophile.
- Responsible for weathering of silicate rocks
- Release carbon dioxide in the atmosphere
- Presence of dissolved mineral make it relevant for therapeutic uses.
- High tourist attraction
- Beneficial for animals during the extremely cold season.
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