Volcanoes Flashcards
What causes Volcanoes
Ocean-ocean, ocean-continent, subduction zone, mantle plumes, rift zones
Magma
is melted rock material beneath the surface.
Lava
melted rock material when it erupts at the surface.
Active Volcano
has erupted in historic times (or at least within the last 10,000 years.)
Dormant Volcano
has not erupted recently but geologically is likely to do so again.
Extinct Volcano
is geologically is unlikely to erupt again.
Plutonic Igneous Rock
cool slowly below the surface
Volcanic Igneous Rock
cool quickly at/near the surface.
Silica Tetahedra
Sio4
Each mineral has a…
Crystallization point
Igneous vs Magma
Magma mixing, melting of surrounding, partial melting, fractional crystallization.
Why does magma have different composition?
Different minerals at different temperature.
Magma mixing and melting of surrounding rock bodies…
are two reasons magma vary in composition.
Fractional Crystallization
another reason magmas vary.
- As magma cools, high temperature minerals form first, if they settle out of the magma, the magma now has a different composition.
At what setting do we find Volcanoes?
80% of volcanic activity is at a divergent plate boundary: 10% is at a subduction zone, and remaining 10% is at mantle plumes.
Subduction Zone carries
water rich oceanic plate into the mantle where the water causes it to partially melt; it may mix with continental crust as it rises upward.
Magma at mid-ocean ridges…
forms from partial melting of the mantle due to lowered pressure from spreading.
* the same process also happens during continental rifting and may eventually cause a mid-ocean ridge to form.
Mantle plumes
can generate magma by partially melting the upper mantle or overriding plate (continental or oceanic)
What happens when a volcano erupts?
When a volcano erupts it produces combinations of lava, pyroclastic debris, and volcanic gas.
- lots of silica makes a magma viscous because silica tetrahedra like to link together.
Three types of lava
Rhyolitic, andesitic, and basaltic
Basaltic lava
has the highest temperature and lowest SiO2 content so has a low viscosity
Andesitic and Rhyolitic
magmas have lower temperatures and higher Sio2 content, so are more viscous.
Basaltic Magma
has the lowest gas content and tends to erupt peacefully
Rhyolitic Magma
has the highest gas content and tends to erupt explosively.
Basaltic Eruptions
basaltic lava is hot, with a low viscosity, low siox, and low gas content
-lava tubes are common features of basatlic eruptions.
Lava Tubes
form as the surface cools, but lava continues to flow beneath the surface.
-Columnar jointing often results as basaltic lava flows cools and contract.
-Pillow basalts form as the lava oozes out and a thin skin cools in cold seawater.
Andesitic/Rhyolitic Eruption
lava is cooler with a higher viscosity, higher Siox content and higher gas content
Andesitic/Rhyolitic Eruption
lava is cooler with a higher viscosity, higher Siox content and higher gas content
- This type of lava flows more slowly and usually not as far. Tends to be explosive
- Pyroclastic debris is common feature.
- Tuff/Tephra is a common product of andesitic/rhyolitic eruptions to form the rock tuff.
- Lahars occur when tephra mixes with water causing deadly flows.
The 3 V’s of Eruption Styles
Viscosity controls lava flow
Volatile abundance controls explosiveness
Volume influences severity eruptions (small or large)
Characteristics of Eruption Style
-Flood basalts are low viscosity, low volatiles, and very large volume
-Icelandic- type eruption are very peaceful eruptions from fissures than build up nearly horizontal layers
-Hawaiian- type eruptions produce higher lava fountains and low cones and may last for years as lava slowly flows downhill
-Shield Volcanoes form from low viscosity, low volatiles, and large volume basaltic lava flows
-Strombolian- type eruption short-lived explosive outburst of pasty lava ejected 10s-100m into the air.
Lava Domes
high viscosity, low volatiles and small volume eruptions that happen after volcano/Plinan eruptions.
Calderas
result from very high viscosity, high volatiles, and very large volume. Small summit of volcanoes.
Where does Mantle Plume magma come from?
Magma erupting at a mantle plume volcano did NOT come all the way from the core/mantle boundary.
How do mantle plumes change through time?
The basalt flows are called the Columbia River Plateau basalts because the river has eroded down through them in many places. Early mantle plume spreads out and is very hot; later it cools down and affects a smaller area.
Movement of Magma
frequent shallow earthquakes
Mantle Plumes are…
most easily studied using seismic waves.
Pyroclastic Flows
can happen because of eruption column collapse.
-Volcanoes put many sizes of pyroclastic debris into the air, the heavier particles fall back and then rush down the side of the volcano.
Lahars
following existing river valleys and quickly fill them with ash deposits. Pre-existing drainage patterns so their path is somewhat predictable.
