Volcanoes

How are volcanoes measured?

Volcanic explosivity index: a relative measure of the explosiveness of volcanic eruptions. Measures how high the ash cloud is, how frequent the eruption is and how big the plume is. 

The more explosive a volcano the less frequent the eruption. 

Types of lava

Basaltic: 

• low viscosity, hot, and runny.
• takes long time to cool and solidify, flows long distances.
• Eruptions are frequent but relatively gentle. 
• Lava and steam ejected. 
• found at constructive plate margins where magma rises from the mantle. 

Andesitic: 

• viscous, less hot, flows more slowly
• Soon cools and solidifies, flowing very short distances. 
• Produces steep-sided, more localised features 
• Eruptions less frequent but violent. 
• Ash, lava, rocks, gas, and steam ejected. 
• found at destructive margins 

Rhyolitic:

• coolest
• thick and stiff (high viscosity traps gases) 
• very violent
• supervolcanoes or composite cone volcanoes. 

VE Index Classification              Nature of eruption                              Type of lava 

Icelandic                          lava flows gently from fissure                        Basaltic

Hawaiian    …