Sample Material For Geography Test

Sample material for Geography Test I Volcanism is the set of geographical process resulting in the expulsion of molten rock, as lava, at or near the Earth’s surface. The most notable product of volcanism are volcanoes, the landforms created when lava and hot particles escape from the Earth’s interior through openings or vent in the Earth’s surface and then cool and solidify around the vents. As such volcanicity relates itself with both the exogenic and endogenic environments. I include all the processes and mechanism that relates them to the origin of magma, gases, vapour, their ascent and ultimate development of various plutonic and surface features. Exogenic volcanicity The exogenic volcanicity includes the wide range of typology. The periodicity of occurrence has been taken as the basis to classify volcanoes Dormant volcano It is the volcano that has not erupted recently but is considered likely to do so in the future. The presence of relatively fresh (within 1000yrs old) volcanic rocks in a volcano suggests its capability of repeat performance. Mt. Baker near Washington-British Columbia border is the prominent example.

Volcanism Exogenic Fissure type Central type Hot springs Solftara Geyesers Mud flow

Endogenic Batholith Laccolith Lappolith Phacolith Duke Sill

Extinct volcano It is the volcano that has not erupted for a very long time and is considered unlikely to do so in future. One indication is the extensive erosion that erodes the core since the last eruption. A true extinct volcano is no longer fueled by a magma source. Emperor seamount chain is the example. Volcanic eruptions range from the quiet oozing of molten basalt from Kilavea volcano in Hawaiian island to the catadysmic explosion of Krakatoa in Indonesia. The quiet fissure type This type of volcano occurs along fracture, fault where slow upwelling results in lava spread over ground. The lava flow depends on the nature of Magma. The entire prominent volcanic plateau excels the example of large territorial coverage by Magma flow. Deccan plateau excel the example of large territorial coverage by Magma flow. Exaples are Deccan plateau India, Colorado plateau (USA) Brazilian shield, Abassinian Plateau (Ethiopia) Arabia plateau (S. Arabia) etc. Geysers are the hot springs from which column of hot water and steam is explosively discharged at intervals. Spring Marks continuous discharge of the same. These are prominently identified with Iceland (Geyser) New Zealand and USA(Yellow stone National Park).

Solftara fumarole is jet of gases issuing from a small vent. Gas temperatures in fumaroles are extremely high (up to 320 0C) Most of the gas (99%) is water. Thus solftara is emitted superheated steam. Volcanic mudflow/Lahar is the water mix down-slope movement of pyroclastic material. Lahar may contain a range of particle sizes from finest ash to enormous boulders. It is often produces on snowcapped volcano and hot pyroclast melts large volume of snow or ice. Columbian Lahar along Andean slope 1985 is the most devastating example. The central type of ejection includes several commonly referred components of volcano. The mobility of molten rock material from below surface is via the vent and ejection mouth crater. The most identified category has been further sub classified into four on the basis of intensity and frequency of occurrence.

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The Hawaiian type The Vesuvian type The Strombolian type The Pelean type

The Hawaiian type is referred to sub aerial basaltic lava flow with precise absence of gaseous constituents. The gaseous constituents being absent, the ejection is quietest. The movement of basaltic magma down slope as burning strings is named as Pele’s hair. The Pahoehoe and AhAha are the two typologies of Magma Movements with temperature as high as 1175 0C. Vesuvian/Pilinian is intense type. Lava is viscous and blocks the vent to increase pressure. Even the core gets shattered in angular fragments. Ash laden cumulus clouds are common consequence. Strombolian is moderate intensity ejection. Pumice, bombs magma and gases are being ejected. These are quiet rhythmic ejections. Pelean is the most disastrous, linked with most viscous Rhyolithic Magma or Andestic magma Nuee ardente or glowing clouds develop as quick condensation develops. Krakatoa (Indonesia) Martinique (Lesser Antilles) are the sites where such ejections have been experienced.

The intrusive volcanicity The intrusive volcanicity is identified with highly viscous magma. The various types of features that develop due t solidification of Magma include most of the intrusions carried on by Magma to the existing cracks or pores. Z Batholith is large Mass of granite. As the hot Magma rises it melts and incorporates the older rocks lying above it. Laccolith is dome like mass, which overlaps the sedimentary rocks. Sill sheet of igneous rocks that beds itself horizontally by the rising magma develops vertical intrusion. Lappolith is the saucer like mass. The ridge and trough development in the bedding plane avails phacolith. Plate Tectonics and Volacanism Volcanism is mostly associated with weaker zones of the Earth’s surface. The plate tectonics theory explains volcanicity mechanisms almost completely. The plate boundaries are the weak zone that marks the activity and determines both nature and intensity of volcanic eruptions. The plate boundaries are classified into three broad groups and volcanicity associates itself with all three. Most of the fissure ejections links itself with divergening or constructive plate margins. The sub-aqueous basaltic ejections result in the constant upwelling and development of Mid Ridges. The development of quiet fissure type ejection is in obvious reference linked with absence of pressure, as gaseous constituents are negligible. Iceland, Hawaiian island and Mid Atlantic ridge are the examples. On the continental plate divergence the intensity of ejection increases, as clear passage for gaseous constituent is not there. Along the Great Rift Valley, Mt. Mulanje, Mt. Rungwe, Mt. Kenya, Mt. Kellimajaro are representative examples. The divergence of African and Somali plates marks the prevalence of Mechanism. Converging plate boundary or Destructive are the crudest spread. The subduction of the oceanic plate avails volcanic activity. Cirrcum-Pacific Belt stretching from West North American coast to East Asian Archipelago also includes the Erebus Mountain of Antarctica. Most of the high volcanic core and Mountains are found in this belt. Mt. Rainear, Mt. Shasta (USA) Mt. Cotapaxi (Ecuador) Mt. Fujishan (Japan) Mt. Mayon (Philippines) are the prominent examples. The belt converges with East Indies archipelago as mid continental belt. The entire category of volcanoes of Alpine

Mountain chain and Mediterranean Sea are included. Mt. Vesuvius, Mt. Etna, Mt. Demavand (Iran) Mt. Poopa (Myanmar) are the prominent cones.