Types of lava

Andestitic Lava

Erupted from Composite volcanoes
Temperature of 800-1000° C
Intermediate silica/ silicon dioxide content at 52-63%
3-4% gas content
forms when an oceanic plate mixes with sea water as it is subducted resulting in a high water and hrdrochloric acid content
Moderate magnesium and iron content
It usually comprises a small volume that progresses no further than the base of the volcano.
Its flow is described as block flow- slow movement forming smooth square shaped blocks as it cools

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Tends to ooze from erupting composite volcanoes
Has the greatest silicon dioxide content at 70%
lowest temperature of any lava type at 650-800° C
Highest viscocity (thickest) of any lava type- due to mineral content
4-6% gas content- viscocity gives it the potential to trap high levels of toxic gases
High sodium and aluminium content
Low magnesium and iron content
Formed from melted lithospheric mantle at an oceanic: continental convergent plate margin
can cause extremely explosive and violent eruptions- resistance to flow causes pressure to build up and gas levels can create massive explosions.

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Usually erupts from shield volcanoes
lowest silica content at 50%
Hottest of all lava types at 1000-1200° C
Lowest viscocity (runniest) - able to flow quickly creating volcanoes with gentle sloping sides
high iron and magnesium content
0.5-2% gas content
low aluminium content
Fastest flowing lava but still possible to out run

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Mount St Helens -Washington

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Mauna Loa-Hawaii

As of January 2013 it hasn't erupted since 1984- its longest period of quiet ever recorded
From the 1880's to the 1920's it erupted every three years on average
Magma compostion is very silica poor- runny lava and non-explosive eruptions
pressure is released more regularly so eruptions are less energetic
1950- erupted 376 million metres cubed of lava which reached the sea in 4 hrs- permanently damaged the village of ho'okena-mauka but didn't cause any deaths

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