Exam 2 part 2 Flashcards
What 3 things determine the viscosity of magma?
1) Composition
2) Temperature
2) Dissolved gases
What does the viscosity determine for magma?
It will determine just how explosive it will be when it erupts from a volcano
How does silica content affect the viscosity of magma?
The higher the silica content there is, the higher the viscosity. The lower the silica content, the lower the viscosity.
Which has higher silica content, felsic rocks or mafic rocks?
Felsic has higher silica content than mafic.
What is Tetrahedra ?
Silica
Which is less viscous, hot magma or cooler magma?
Hotter magma is less viscous
How can gases affect magma?
Because gases extend in magma when they near the surface, the violence of the magma’s eruption will be determined by how easily the gases can escape.
Which type of magma/lava is more explosive, Basaltic or Andesitic?
Andesitic lava/magma are more explosive than Basaltic
What type of behavior does basaltic lava have?
It has a fluid like behavior
What are two types of basaltic lava?
1) Pahoehoe lava
2) Aa Lava
What is the difference between Pahoehoe lava and Aa lava?
Pahoehoe lava resembles a twisted ropey texture while Aa lava is rough, jagged and bulky.
What are the dissolved gases in magma?
Mainly water and Carbon Dioxide
What are pyroclastics?
They are fragments extruded from a volcano
What are 4 types of pyroclastics?
1) Ash and dust (Glass fragments)
2) Lapilli (walnut-sized pieces of material)
3) Pumice
4) Particles bigger than Lapilli
What is Lapilli made of?
Pumice
What is the first to fall from a volcanic eruption?
Lapilli
Why do volcanoes erupt?
Landslides
What are the 4 features of a volcano?
1) Opening at the summit
2) Craters/Calderas
3) Vent spaces connected to the magma chambers
4) Fumaroles
What are craters and calderas and what is the difference between them?
Craters and Calderas are both depressions in the volcano but craters are smaller than 1km and calderas are lager than 1km
What are the 3 types of volcanos?
1) Shield volcanoes
2) Composite volcanoes
3) Cinder cone volcanoes
What are the 4 factors of Shield volcanoes?
1) Broad and slightly domed-shaped
2) Cover large areas
3) Mild eruptions
4) Usually have large calderas
What are the 5 factors of cinder cone volcanoes?
1) Built from ejected lava
2) They have steep slope angles
3) Small in size
4) Frequently occur in groups
5) After the gases are gone the lava will flow only as a liquid under the volcano
What are the 6 factors of composite volcanoes?
1) Most are located adjacent to the pacific ocean
2) Large, thousands feet high and miles wide
3) Composed of lava flows and pyroclastics
4) Most violent eruptions
5) Lava flows down a different side of the volcano each eruption
6) Over time they build themselves back up after collapsing
What is Nu’ee Ardente?
It is a deadly pyroclastic flow that is known for glowing avalanches and can move at speeds of 200km per hour
What is a Lahar?
It’s a volcanic mudflow that moves down stream valleys and volcanic slopes
What is a caldera eruption?
When a volcano collapses after an eruption and leaves a large depression.
What sometimes happens in the calderas of volcanoes?
Sometimes a lake will form in the caldera
What is a pyroclastic flow?
When a pyroclastic cloud (That erupted from a volcano) collapses and flows downwards
What are volcanic fissures?
They are fluid basaltic lava extruded from crustal fractures
What is a lava plateau?
A large flat area in which highly fluid lava flowed over and solidified into a flat surface
What are lava domes?
Bulbous mass of congealed lava from an explosive eruption of gas-rich magma
Why do lava domes form?
Usually when the volcano is attempting to build itself back up after collapsing.
What are volcanic necks?
They are vents inside the volcanic cone that are left over after the volcanic cone has been worn away by erosion
What are volcanic pipes?
They are short conduits underneath the volcano that connect a magma chamber to the surface
What is a pluton?
It is when magma is cooled and solidified in sheets deep in the earth
What is the difference between concordant and discordant plutons?
Concordant plutons are parallel to the surround bedrock while dis-concordant isn’t parallel
What is a dike and what is a sill?
A dike is a discordant pluton and a sill is a concordant pluton
What is a Laccolith?
Similar to a sill, mushroom shaped mass, arches overlaying strata.
What is a Batholith?
It is the largest intrusive body, larger than 100km squared surface exposure and are usually at the cores of mountains
What is a fumarole?
A hole in a volcano in which steam rises
