Lava

"LAVA"

What is Lava?

Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C (1,292 to 2,192 °F). The resulting structures after solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.

Lava is made up of crystals, volcanic glass, and bubbles (volcanic gases). As magma gets closer to the surface and cools, it begins to crystallize minerals like olivine and form bubbles of volcanic gases. When lava erupts it is made up of a slush of crystals, liquid, and bubbles. The liquid "freezes" to form volcanic glass.

Chemically lava is made of the elements silicon, oxygen, aluminum, iron, magnesium, calcium, sodium, potassium, phosphorus, and titanium (plus other elements in very small concentrations. Have a look at the background information in Minerals, Magma, and Volcanic Rocks.

Lava flows are the least hazardous of all processes in volcanic eruptions. How far a lava flow travels depends on the flows temperature, silica content, extrusion rate, and slope of the land. A cold lava flow will not travel far and neither will one that has a high silica content. Such a flow would have a high viscosity (a high resistance to flow). A basalt flow like those in Hawai'i have low silica contents and low viscosities so they can flow long distances. Such a flow can move as far away as 4 km from its source and have a thickness of 10 m (Bryant, 1991). These flows can move at rates of several kilometers per hour (Scott, 1989). More silica-rich flows can move as far away as 1.3 km from their sources and have thicknesses of 100 m (Bryant, 1991). These flows can move at rates of a few to hundreds of meters per hour (Scott, 1989). If a lava flow is channelized or travels underground in a lava tube then the distance it travels is greatly extended.

Lava flows as you can see don't move very fast so people rarely get killed by them. However, lava flows are very hot (between 550 degrees C and 1400 degrees C) and can therefore cause injuries. People have burnt their skin, charred their eyebrows, and melted the soles of their boots from being near or on a hot lava flow. Lava flows don't cool instantaneously. It can take days to years for a lava flow to completely cool.

Lava flows are streams of molten rock that pour or ooze from an erupting vent. Lava is erupted during either nonexplosive activity or explosive lava fountains. Viscous dacite and rhyolite flows often form steep-sided mounds called lava domes over an erupting vent.

Lava behavior

Toes of a pāhoehoe advance across a road in Kalapana on the east rift zone of Kīlauea Volcano in Hawaii, United States . In general, the composition of a lava determines its behavior more than the temperature of its eruption. The viscosity of lava is important because it determines how the lava will behave. Lavas with high viscosity are rhyolite, dacite, andesite and trachyte, with cooled basaltic lava also quite viscous; those with low viscosities are freshly erupted basalt, carbonatite and occasionally andesite.

References:

https://en.wikipedia.org/wiki/Lava

http://volcano.oregonstate.edu/what-lava-made

https://volcanoes.usgs.gov/vhp/lava_flows.html