Volcanism

Discuss, with examples, the influence of volcanism and diastrophism on the evolution of landscape. (200 Words)

Volcanism and diastrophism are two endogenic processes of geomorphology.
Diastrophism covers movement of solid (plastic) crust material, as opposed to movement of molten material which is covered by volcanism. These forces derive their energy from changes such as radioactivity, chemical recombination, expansion or contraction or displacement of molten materials which Occurs in the interior of the earth.
These processes creates, modify and continuously affect the landscape of the earth.
A volcano is a place where gases, ashes and/or molten rock material – magma/ lava escape to the ground. in this process, molten rock material called magma in asthenosphere find their way to the surface where it is called as lava. The way a volcano erupts and the materials that make up the magma and lava of a particular volcano have a lot to do with the formation of the volcanic landforms, such as craters, calderas, lava domes and lava plateaus. e.g.. if magma seeps through cracks in the ocean floor, the lava hardens, helping to build underwater mountains and new segments of ocean floor.
Some of the landforms associated with volcanism are:
-> Craters: crater is a bowl-shaped depression at the top of a volcano caused by past volcanic eruptions. A volcanic crater is relatively small, usually spanning about a half a mile in diameter or less, and can fill with water to form a crater lake.
-> Caldera: If a volcanic eruption causes the magma chamber to empty, the volcano can implode, forming a larger depression known as a caldera. e.g.. Yellowstone caldera.
-> Volcanic domes: Volcanic Domes result from the extrusion of highly viscous, gas poor andesitic and rhyolite lava. Since the viscosity is so high, the lava does not flow away from the vent, but instead piles up over the vent.
-> Basalt plateau: Basalt plateau is formed due to outpouring of extremely large volume of low viscosity basaltic magma from fissure vents. The basalts spread huge areas of relatively low slope and build up plateaus. e.g.. Deccan plateau, Columbian plateau.
Other landforms associated with volcanism are Batholiths, Laccoliths, sills, dykes, hot spring, geysers etc.
Processes that move, elevate or built up portions of earth’s crust are called diastrophism. Diastrophic forces operate very slowly and their effects become discernible after thousands and millions of years. These forces are also termed as constructive forces, affect large areas of earth and produce meso-level reliefs such as mountains, Plains, Plateaus, lakes, big faults etc.
It include:
i) Orogenic processes: Mountain building through severe folding and affecting long and narrow belt of earth’s crust. These processes acts tangentially and may be divergent or convergent.
ii) Epirogenic processes: Uplift or wrapping of large parts of earth’s crust or emergence/submergence of crust.
iii) Earthquakes involving local and relatively minor movements
iv) Plate tectonics involving horizontal movement of crustal planes.
Through these processes, there can be faulting and fracturing of the crust. All these processes cause pressure, volume and temperature changes which in in turn includes metamorphism of rocks.
What are the causes of volcanic eruption? Examine why it’s considered as hazard. Also discuss why predicting volcanic eruptions is said to be a very difficult task. (200 Words)
Causes:
  1. subduction of one plate under other in case of converging plate boundary and resultant melting of rocks due to high temp and pressure which rises along the fissures of rocks.
  2. In case of diverging boundaries thinning of upper crust leads to reduction in overlying pressure of rocks causing decrease in rock melting point and formation of magma which rises and erupts as lava from fissure volcanos.
  3. some continental volcanoes located away from plate boundaries due to stressing of plates and creation of faults.
reasons for hazard:
  1. air pollution and resulting effects on human ,livestock ,air transport, climate, ozone
  2. loss of human life and property due to primary effects of lava and ashes, rocks etc.
  3. secondary disasters like tsunami, earthquakes, mud flow, floods etc. caused by volcanic eruption.
  4. Climatic changes due to large amount of dust and ash in air which causes small ice age.
  5. Loss of vegetation and wildlife of surrounding areas.
Difficult to detect:
  1. no defined sequence of events causing eruption.
  2. subsurface phenomena with very high temperature so most scientific instruments fails to work
  3. sudden phenomena which provides very less time for analysis and prep.
  4. Existing methods using seismic analysis not completely reliable
The greatest concentration of volcanoes is located in the Circum – Pacific region, known as ‘Pacific Ring of Fire’. Examine why and also explain features of these volcanoes. (200 Words)
The Pacific “Ring of Fire” is a string of volcanoes and sites located on most of the Earth’s subduction zones having high seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of all earthquakes occur along the Ring of Fire.
The Pacific Plate hits other plates nearby and that causes them to sink because of O-O or O-C convergence. The crust melts producing the magma that feeds the different volcanoes in the Pacific Ring of Fire or it will help produce new volcanoes. The Ring of Fire is the result of plate tectonics. Most tectonic activity in the Ring of Fire occurs in these geologically active zones.
It is believed that the Pacific Ring of Fire has a total of 452 volcanoes. Most of the active volcanoes on The Ring of Fire are found on its western edge, from the Kamchatka Peninsula in Russia, through the islands of Japan and Southeast Asia, to New Zealand.
Vital volcanoes are Mt Fuji in Japan, Mt. Saint Helens and Mt. Rainier in the American North West, Krakatoa in Indonesia, Mauna Loa in Hawaii, and Galeras in Colombia and Sangay in Ecuador. These volcanoes are well known and some those could be very dangerous because of their activeness, icy caps and highly populated areas around them with some famous tourist spots.