Study Geography notes on Vulcanicity for Secondary. Useful for revision, homework, and exam preparation in Zimbabwe.
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Volcanicity Volcanoes are classified as; Active - Volcanoes that have erupted recently Dormant - Volcanoes that have not erupted recently but have done in the last 2000 yrs Extinct - Volcanoes that have not erupted for many thousands of years VULCANICITY Is the process through which molten rock (magma) and gases from interior moves into the earth's crust or on to the earth surface along lines of weakness (fault lines). What causes vulcanicity Deep inside the earth heat and pressure exerted by the crust cause rocks to melt forming molten rock known as magma, which is forced to rise along the lines of weakness (fault lines). Features formed: - features formed can either be; 1. Extrusive features: - the magma reaches the surface, cools and solidifies. When magma reaches the surface it is known as lava. 2. Intrusive features: - magma solidifies below the earth's surface forming intrusive volcanic features. Types of Lava 1. Acidic lava: very thick, traps a lot of gas, water, rich in silica content violent eruption and lava solidifies very quickly builds up steep cones. 2. Basic lava: this is a form of fluid poor in silica content flows for a very distance before it solidifies, it builds up gently sloping cones, lava plateau and plains 3. Pyroclasts (Heated lava): when lava is short into the air, it breaks down into small fragments or pieces (pyroclasts), which usually falls to the ground and form layers of Ash/cinder. Layers of ash mix with layers of lava to form composite cones. Extrusive features When lava magma reaches the surface, it forms a variety of features depending on the type of lava and the nature of the eruption. The following are the common features; 1. Lava(Plateaus - formed from fissure eruptions of basic lava. When plates are moving apart, they create fissures through which magma will be ejected rather than through a central vent. The lava flows for very long distances before solidifying filling up depressions and forming a plateau rather than a conical hill. The Tutor on the Go Page 1 Print to PDF without this message by purchasing novaPDF (http://www.novapdf.com/)