Lesson 10 - Volcanic Hazards Flashcards
What are the 3 states of volcano?
Active - Erupted in living memory
Dormant - Erupted within historical record
Extinct - Unlikely to erupt again, no eruption in last 10,000 years
What are the 3 lava compositions?
Rhyolitic
Andesitic
Basaltic
Describe the characteristics of rhyolitic lava
Highest silica content (63%+)
Most viscous
650-750’C
Create most destructive/explosive eruptions
Short lived + intermittent eruptions
Why do rhyolitic lavas create the most explosive eruptions?
Viscous lavas cause blockages in vents
Pressure builds
Gases trapped
Prevents gas bubbles from expanding
Pressure released upon eruption
Where are rhyolitic lavas generally found?
Subduction zones at destructive plate boundaries
Describe the characteristics of andesitic lava
52-63% silica content
Intermediate composition
750-950’C
Cools to form andesite
Short lived + intermittent eruptions
Eruptions less explosive than rhyolitic
Where are andesitic lavas generally found?
Convergent boundaries
Due to melting of subducted plates containing sediments
Describe the characteristics of basaltic lava
45-52% silica
905’C+
Least viscous
Flows easily
Gases escape easily
Eruptions frequent + less violent
What is this lava also referred to as?
Mafic lava
As it contains higher % of magnesium and iron
Where are basaltic lavas generally found?
Mid-ocean ridges - Plates pulling apart, lava fills gap
Shield volcanoes
Define silica
Molecule formed of silicon + oxygen
Dictates fluidity of magma
Higher silica content, greater viscosity
Recall the characteristics of composite volcanoes
Formed by alternating layers of solidified lava + ash
Steep slopes (Above 10*)
High gas pressure + explosive
Composed of different materials
Where are composite volcanoes generally found?
Destructive margins
Recall the characteristics of shield volcanoes
Gently sloping sides
Formed by frequent, gentle eruptions of thin, fluid lava
Layers of solidified lava only
Where are shield volcanoes generally found?
Constructive margins
Hot spots
