Volcanoes

• Volcanoes from only at constructive and destructive plate boundaries
• Nuees Ardentes (pyroclastic flows) are formed of hot gasses over 800 degrees and tephra (ash). After ejection from a volcano, they can flow down the side of a mountain at speeds of over 700km/h
• Laval flows is when molten rock flows onto the surface. Acid lava solidifies very quickly but basic lava (basaltic) tends to flow some distance before solidifying.
• Lahars occur when volcanic ash mixes with water (snow melt, heavy rainfall) flowing downhill. They are volcanic mudflows.
• Magnitude is measured using the volcanic explosivity index (VEI) which is a logarithmic scale. Critics point out it doesn't take into account gas emissions.
• Gases such as carbon dioxide, carbon monoxide, sulphur dioxide and chlorine can be emitted by a volcano. This can lead to acid rain
• Tephra is the solid matter ejected by a volcano into the air. It ranges from volcanic bombs to ash.