Y1,S1 - Natural Hazards Flashcards
What is magma generated by? (HINT- 3 factors)
1.Increased temperature
2.Decreased Pressure
3.Adding Volatile elements
What is the upper mantle made of?
Peridotite
What happens to the temperature of the mantle as its depth increases?
Temeprature increases
What happens when the pressure or temperature of peridotite (upper mantle) is altered, causing it to pass the geotherm?
Lithospheric mantle is created
Where is water trapped in the upper oceanic crust?
Crystals
What happens to temeprature and pressure as depth of the mantle increase?
They both increase
Why does subducting oceanic crust alter the liquedous conditions of the upper mantle?
Water is released as crystals, it was previously stored in,melt
What does increasing the liquedous conditions of magma result in?
Magma ascension (volcano formation) over long time scales (millions of years)
In most places does magma rise to the surface due to an increase in temperature or decrease in pressure, as it reaches the geotherm?
Decrease in pressure
Give an example of where magma is reaching the geotherm due to a decompression?
East African rift valley
What causes hotspot volcanism?
Upwelling of magma (mantle plume) from the mantle-outercore boundary, despite being a solid it moves up towards the surface over tens/millions of years, driven by byouyancy
what is magma?
Multiphase mixture of melt (liquids), crystals (solids) and gas (bubbles)
Why do volatiles in magma drive the eruption?
Because they from bubbles which accelerate the magma upward
What is magma mixing?
Hot magma replenishment which disrupts the chamber
Why deoes magama mixing cause eruptions?
The increased temperature of magma replenishment mixes with the cool magma sitting in the reservoir, destablising the chamber. Pressure and volume changes as crystals and vesicles mix, causeing acceleration.
Ultramafic lava contains…
Peridotite
Low SiO2 content
As crystal content in lava increases, what else increases (3 factors) ?
Silica content
Na and K content
As silica content increases does temperature increase or decrease?
decrease
Name the 4 different magma compositions from highest SiO2 content to lowest…
1.Felsic
2.Intermediate
3.Mafic
4.Ultramafic
What main factor (mineral) changes the viscosity of magma?
Silica content
Name the 5 types of magma in order from highest to lowest viscosity?
1.Rhyolite
2.Andecite
3.Dacite
4.Basalt
5.Komatite
Describe basaltic volcanoes?
-Typical temp. 1000-1200C
-SiO2 45-52 wt% [mafic]
-High conc. of Fe, Mg, Ca
-Low conc. of Na, K, Si & H2O
-Typically contains olivine, plagioclase (Ca-rich) & pyroxene
-Low viscocity (flows easily)
-E.g. Kileaua , Mt Etna & Bardabunga
Decribe Andesitic volcanoes?
-Typical temp. 800-900C
-SiO2 52-63 wt% [Iintermediate]
-lower conc. of Fe, Mg, Ca than basalt
-higher conc. of Na, K, Si & H2O than basalt
-Typically contains amphibole, plagioclase & pyroxene
-E.g. Tungurahua, Fuego & Soufiere hills
Describe dacitic volcanoes?
-Typical temp. 800-900C
-SiO2 63-70 wt% [Iintermediate]
-Often crystal rich
-Viscuous - eruptions can be highly explosive
-Typically contains amphibole, plagioclase (Na-rich), mica & pyroxene
-E.g. Mount St Helens & Pinatubo