Lava composition and behavior

Lava composition 

These classes are primarily chemical; however, the chemistry of lava also tends to correlate with the magma temperature, its viscosity and its mode of eruption Igneous rocks, which form lava flows when erupted, can be classified into three chemical types;, and (four if one includes the super-heated

Felsic lava

. The high viscosity and strength are the result of their chemistry, which is high in, and, forming a liquid rich in and, which thus has a higher viscosity than other magma types. 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 tens of kilometres, such as in the of the northwestern United States.

(or silicic) lavas such as and typically form or "coulees" (which are thick, short lavas) and are associated with (fragmental) deposits. Most Silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias.

Intermediate lava

such as in the Poorer in aluminium and silica than felsic lavas, and also commonly hotter (in the range of 750 to 950 °C), they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form.

Mafic Lava

The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile or " fields", because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath a solidified crust. Most basalt lavas are of or types, rather than block lavas. Underwater they can form " which are rather similar to entrail-type pahoehoe lavas on land.