Volcanism and Landform Formation
Denudation upon the forms produced by vulcanicity results in the evolution of a volcanic landscape. In the views of F.J. Monkhouse, “The product of vulcanicity vary from hardest of lavas to the softest of ashes often in close juxtaposition.”
It has been witnessed that volcanic activity creates unique and distinct landscapes. For example, Mount Vesuvius destroyed the city of Pompeii in A.D 79 towers over the city of Naples in Italy. Similarly, Mount Etna (Sicily) pervades the physiography of the entire area. The volcanic landscapes are common along the Pacific rim from Southern Chile to New Zealand and Indonesia through Java. On the Asian side of the Pacific, these landforms are almost associated with island areas. Japan’s Mount Fuji towers over the area located South West of Tokyo. There are several types of volcanic landforms which include the following:
(1). Volcanic Plateaus:
Fluid Lava comprising silicates, iron, and magnesium produces flat volcanic plains in the shape of plateaus. These plateaus may cover vast areas to the extent of 250,000 sq. km. A number of repeated eruptions increase the thickness of the layers of extrusive igneous rock material. A volcanic plateau has a higher elevation than a volcanic plain. These landforms are found in Columbia Plateau, Deccan (India), Ahaggar (Sahara), and West of Iresti mountains (East Africa).
(2). Volcanic Cones:
Volcanic Cones are the most common volcanic landforms. The cones are found in the following varieties:
⦁ Spatter Cones:
⦁ Tephra Cones
⦁ Composite Volcanic Cones
⦁ Complex Volcanic Cones
(3). Volcanic Rifts:
Explosive fissure eruptions create volcanic rifts. Fragments and fine powder are found on both sides of these rifts.
(4). Volcanic Spines:
When lava is pushed upward from the crater volcanic spines are formed. These spines crumble shortly after their formation. Pele Spine (California) offers a good example of this type of landform.
(5). Welded Tuff:
Violent fast gases disrupt the liquid phase after eruptions of felsic lava. Thus hot lumps and pockets form a mixture called tephra, which flows at a speed of 30 to 100 km per hour. As a result, the layers of hot tephra are called Welded Tuff. It is a fine example of a volcanic landform.
Caldera is a steep-walled circular volcanic basin formed by the collapse of a volcano whose magma chamber empties out. It can also result from a powerful eruption that flows off the peak and crater of a volcano. Example of calderas are as under:
⦁ Karakatoa (Indonesia)
⦁ Mount Aso (Japan)
⦁ Morogoro (Tanzania)
The mouth of a Volcano having a diameter of 1.5 km or less is known as a crater. It is mostly found at the top of a volcanic cone.
(8). Geyser and Hot Springs:
A hot spring that expels jets of heated water and steam is known as a Geyser. Similarly, a hot spring is a geyser whose water temperature averages 10 degrees celsius. It emanates from crystal zones that contain a magma chamber near the surface of Earth.