Lava
Lava starts life as molten rock, which forms between 50-150 km below the surface of the Earth. When it is still underground this molten rock is called magma. Once it reaches the surface to erupt and flow down the side of a volcano, it is called lava.

In general, the hotter the lava the more fluid it is and the faster it flows. Hawaiian lavas tend to be at the hot end of the range. When they erupt they are about 1,175º (2,140º F). The hottest lava is yellow-orange. As temperature rises the colour goes from dull red through orange, yellow-orange, yellow, green, blue and then to ultraviolet and beyond. The sun's ‘colour’ is yellow-green, corresponding to a temperature of somewhere around 5,000º (lava is generally less than 1,200º C).

Composition
Magma varies in composition and produces different lavas, according to the minerals deposited in the original rock - from fluid, fast-moving basalt to slower, more viscous andesite. Originating many tens of miles beneath the ground, lava contains crystals, fragments of surrounding (unmelted) rocks and dissolved gases, but it is primarily composed of oxygen, silicon, aluminium, iron, magnesium, calcium, sodium, potassium, titanium and manganese. Very hot, gas-rich lava, containing lots of

Pyroclastic flows
Pyroclastic flows are deadly avalanches containing hot volcanic gases, ash and rock fragments. On steep volcanoes, pyroclastic flows can reach speeds of over 100 miles per hour. They can incinerate, burn and asphyxiate any life in their path and one breath of the deadly gas can sear a human’s internal organs.

Lahars
Lahars are volcanic mudflows created when water (from rain or melt-water from glaciers) and ash mix. This deadly combination can have devastating results on the surrounding area. When lahars settle they can be metres thick and as hard as cement. Lahars can occur long after a volcanic eruption.