Please enable JavaScript.
Coggle requires JavaScript to display documents.
Volcanoes - Coggle Diagram
Volcanoes
Lava Characteristics
Felsic (Dacite and Rhyolite)
Felsic (or silicic) lavas such as
rhyolite
and
dacite
typically form lava domes or "coulees" (which are thick, short lava flows)
Felsic lavas have high gas content and therefore usually are released on to the surface as part of
violent eruptions
as pyroclastic material
the
high viscosity
means that usually when this lava does flow it
only travels a very short distance
Felsic magmas can erupt at temperatures as low as
650 to 750*C
. Unusually hot (>950*C) rhyolite lavas, however, may flow for distances of many ten of kilometres, such as in the Snake River Plain of the North-Western United States
Where is Felsic lava found
usually associated with
subduction and convergent plate margin
as found where there is a higher gas content (due to melting of continental crust as magma rises)
Intermediate lava - Andesite (volcanic rock)
intermediate lava has a composition that falls in between that of mafic lava (runny) and that of felsic lava (very thick)
intermediate lava flows more readily than rhyolitic lava, but not as easily as basaltic lava
Eruptions are characterised by a
mixture of explosive activity and lava flows
such eruptions form
composite volcanoes
, built up of altering lava flows and pyroclastic deposits (deposits of debris ejected from the volcano). Composite volcanoes such as Mt. Fuji, in Japan, and Mt. Rainier, in Washington, are cone shaped.
this means the Andesitic lava is usually found at
convergent plate margins
Andesitic Lava/Volcanic Rock
Andesite generally produces
blocky lava
here, the surface contains smooth-sided, angular fragments (blocks) that are not as splintery or vesicular as A'a lava fragments
the blocky nature of these flows is attributed to the
higher viscosity of andesite
andesite commonly erupts from
stratovoclanoes
, where they form small-volume flows that typically
advance only short distances
down the flanks of a volcano
Mafic Lava (Basalt Rock)
basalt is the usually hard and black volcanic rock formed from (liquid) Mafic lava
Mafic lava contains less than about 52 percent silica (SiO2) by weight
Lava has a low viscosity (resistance to flow)
the low viscosity allows volcanic gases to escape without explosive eruptions Basaltic lava is
erupted at temperatures between 1,100 to 1,250*C
Where Basaltic Lava is found
basaltic magma is formed by partial melting of material from the upper mantle, and is therefore typical for volcanism at
hot-spots
(Hawaii)
Basaltic lava flows can be subdivided into two end-member
structural types
, according to their flow surfaces:
Pahoehoe lava
smooth, billowy, or ropy surfaces
A'a lava
fragmented, rough, sometimes spiny, or blocky surface