Post on 24-May-2018
transcript
VolcanoesIt’s all about the magma
What qualifies as a volcano?Any vent in the Earth’s surface that magma is expelled through
So what is magma?Liquid rock that forms under Earth’s surface
Why is it liquid?
How does magma form?1. High temperatures2. Lower the pressure (what?)3. Add water (no kidding)
Why would magma come to the surface?Lighter than surrounding rock
Pressure
Can create more magma by melting surrounding rock
LavaOnce magma gets to the surface, it changes its name to lava
It’s the lava that builds the part of the volcano you can see
Where do volcanoes happen?1. subduction
zones2. mid-ocean
ridges3. hot spots
Subduction ZonesOne tectonic plate moves under another
● ocean vs. continent - Cascades● ocean vs. ocean - Aleutian Islands
Mid-ocean RidgesThe largest amount of magma coming to the surface
Underwater volcanos
Pillow lava
Iceland
Hot SpotsNot at plate boundaries - in the interior
Mantle plumes that remain stationary (stay in place)
Hawaii
Back to MagmaThe type of magma determines the type of eruption
Viscosity (resistance to flow)● low viscosity - runny or liquid● high viscosity - thick or sticky
Depends on what it is made of and trapped gas● Mafic: magnesium and iron, dark colored, runny
○ more common in ocean plates
● Felsic: silicates, light colored, sticky○ more common in continental plates
Quiet EruptionsLow viscosity
● Mafic magma● gas escapes easily● oceanic volcanoes
○ underwater○ Hawaii○ Japan
Explosive EruptionsFelsic lava
● cooler and stickier● more trapped gas● continental volcanoes
What magma becomes: Lavaassociated with quiet eruptions
flows out of volcanoes
rock that results depends on speed of flow and speed of cooling
What magma becomes: Pyroclasticassociated with explosive eruptions
materials that are thrown into the air
rock that results depends when and where it cooled and solidified
Pyroclastic materials1. volcanic dust - tiny particles from trapped gas exploding cooled lava2. volcanic ash - slightly larger particles formed the same way3. lapilli (little stones) - little lava blobs that cool in midair4. volcanic bombs - big lava blobs that cool in midair5. volcanic blocks - solid rock blasted from the vent
Back to MagmaThe type of eruption determines the type of volcano
Lava vs. pyroclastics determine the shape of the cone
Shield VolcanoBroad and sloping
Quiet eruptions - lava flows
covers a large area, builds slowly
Cinder Cone
Very steep slopes
Explosive eruptions - pyroclastic materials
Not usually very large
Composite VolcanoBoth types of eruptions
Alternating layers of lava and pyroclastics
Form large volcanic mountains
CalderaThe end of a volcano’s life cycle
Magma chamber empties
Volcano collapses
Huge crater left at the surface
Yellowstone
Questions?