Volcanoes and Lava Flashcards
What are the three main types of lava?
Basaltic, andesitic and rhyolitic.
What characterises basaltic lava?
Generally, basaltic lava consists of 52 percent silica or silicon dioxide (SiO2). It has a high iron and magnesium content. It has a relatively low viscosity, when compared to other types of lava. It is the fastest flowing lava. Basaltic lava is commonly expelled from shield volcanoes, and it usually flows in the Pahoehoe or A’a style.
What characterises andesitic lava?
The SiO2 content of andesitic lava is between 52 and 63 percent of its composition. It has a higher viscosity than basaltic lava and thus flows at a slower rate. Lava domes are commonly produced as andesitic lava is forced to the surface. Andesitic lava typically originates from stratovolcanoes and usually comprises a small volume that progresses no further than the volcano’s base. Its flow is described as block flow.
What characterises rhyolitic lava?
Rhyolitic lava has the highest viscosity of any type of lava, and it has the greatest content of SiO2. Typically, the SiO2 content of rhyolitic lava is greater than 68 percent of its total composition. It flows much slower than andesitic and basaltic lava. Rhyolitic lava tends to ooze from erupting stratovolcanoes, usually after violent pyroclastic flows.
Name the four main types of volcano?
Shield, composite, lave domes and cinder-cone.
What characterises a shield volcano?
These are large, broad volcanoes that look like shields from above – hence the name. The lava that pours out of shield volcanoes is thin, so it can travel for great distances down the shallow slopes of the volcano. These volcanoes build up slowly over time, with hundreds of eruptions, creating many layers. They’re not likely to explode catastrophically.
What characterises a strato/compostie volcano?
Stratovolcanoes comprise the largest percentage (~60%) of the Earth’s individual volcanoes and most are characterized by eruptions of andesite and dacite lavas that are cooler and more viscous than basalt. These more viscous lavas allow gas pressures to build up to high levels (they are effective “plugs”), therefore these volcanoes often suffer explosive eruptions.
Stratovolcanoes are usually about half-half lava and pyroclastic material, and the layering of these products gives them their other common name of composite volcanoes. They have a typical conical shape.
What characterises a cinder-cone volcano?
They occur when particles and blobs of lava are ejected from a volcanic vent. The lava is blown violently into the air, and the pieces rain down around the vent. Over time, this builds up a circular or oval-shaped cone, with a bowl-shaped crater at the top. Cinder cone volcanoes rarely grow larger than about 1,000 feet above their surroundings.
What causes volcanic eruptions and volcano formation?
Magma rises through cracks or weaknesses in the Earth’s crust. When this pressure is released, eg as a result of plate movement, magma explodes to the surface causing a volcanic eruption. The lava from the eruption cools to form new crust. Over time, after several eruptions, the rock builds up and a volcano forms.
How are island arcs formed?
As a lithospheric slab is being subducted, the slab melts when the edges reach a depth which is sufficiently hot. Hot, remelted material from the subducting slab rises and leaks into the crust, forming a series of volcanoes. These volcanoes can make a chain of islands called an “island arc”.
What characterises a lava dome?
Volcanic or lava domes are created by small masses of lava which are too viscous (thick) to flow very far. The magma from volcanic domes just piles up over and around the vent. The dome grows by expansion of the lava within, and the mountain forms from material spilling off the sides of the growing dome. Lava domes can explode violently, releasing a huge amount of hot rock and ash.
What is a dormant volcano?
A dormant volcano is an active volcano that is not erupting, but supposed to erupt again.
What is an active volcano?
An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.
What is an extinct volcano?
An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.
Where are composite volcanoes commonly found?
Composite volcanoes are common along convergent plate boundaries. When a tectonic plate subducts, it melts. This creates the thick magma needed for these eruptions. The Pacific Ring of Fire is dotted by composite volcanoes.
