How can silica content of the magma affect the volcanoes shape?
The silica content of the magma determines how thick the magma is, how easily it flows and how easily dissolved gases within the magma can escape; therefore the silica content determines the characteristic of the volcanic eruption and the shape and size of the resulting volcanic cone. Gas readily escapes from the lava.
What produces a volcano with gentle slopes?
Shield volcanoes Where a volcano produces low viscosity, runny lava, it spreads far from the source and forms a volcano with gentle slopes: a shield volcano. Most shield volcanoes are formed from fluid, basaltic lava flows. Mauna Kea and Mauna Loa are shield volcanoes.
Which type of volcano has a very broad shape with gentle slopes?
Shield volcanoes
Shield volcanoes are huge, gently sloping volcanoes built of very thin lava spreading out in all directions from a central vent. They have wide bases several miles in diameter with steeper middle slopes and a flatter summit. The gentle convex slopes give them an outline like a medieval knight’s shield.
Which type of rock has the greatest silica content?
Felsic rocks have the highest content of silica, and are predominantly composed of the felsic minerals quartz and feldspar. These rocks (granite, rhyolite) are usually light coloured, and have a relatively low density. Intermediate rocks have a moderate content of silica, and are predominantly composed of feldspars.
How is the silica content of magma related to volcanism?
It is the silica content that controls the viscosity of the magma, and hence the nature of the volcanism that is seen. The low levels of silica mean that Hawaiian magma has a low viscosity, which explains why we see lava readily cascading downslope, and being churned up in the air in great fire fountains.
Why do basaltic volcanoes have a gentle slope?
Because mafic lava is low viscosity, when it erupts from a volcano it flows downslope away from the vent, gradually cooling and crystallizing. Because of the relative ease of flow, basaltic volcanoes are broad, with gentle slopes. They don’t have the stereotypical steep volcanic cone shape.
Why are stratovolcanoes steeper than shield volcanoes?
Stratovolcanoes (also called Composite Volcanoes) Have steeper slopes than shield volcanoes, with slopes of 6 to 10 o low on the flanks to 30 o near the top. The steep slope near the summit is due partly to thick, short viscous lava flows that do not travel far down slope from the vent.
What kind of volcano has a steep slope?
Oftentimes, the pressure builds up enough to produce large pyroclastic eruptions. Alternating eruptions of lava and pyroclasts produce large, layered volcanoes with steep slopes. The well-known volcanoes of the world are composite cone volcanoes.