Earth Science, Tarbuck Chap 6 Flashcards
Mafic magmas have
Lower Silica Content, Lower Gas content, Erupt at higher temperatures
Felsic Magmas have
Higher Silica Content, Higher Gas Content, Erupt at Lower temperatures
Magmas generated by melting of mantle rocks tend to have what composition
Mafic Composition
Largest quantity of basaltic magmas is erupted where
Mid-Ocean Ridges and Hot-Spot Volcanism
What happens in Continental Crust that changes magma generated by partial melting to have a more intermediate composition
the magma usually is denser than overlying continental crust, resulting in the magma pooling at the crust-mantle boundary. This causes overlying crust to be melted and forming a more silica rich mix as the magma then continues to rise.
The two primary factors that determine how magma erupts are its
Viscosity and Gas content
What are Effusive Eruptions
Eruptions that are quiet/non-violent
What does viscosity measure
a fluid’s mobility
magma’s viscosity depends primarily on its
Temperature and Silica Content
The more silica in a magma,
The more viscous it will be
The hotter the magma,
the more fluid it will be
The most abundant gasses in a magma is
Water vapor and carbon dioxide
Most Felsic Magma tend to extrude ____ instead of lava
Volcanic Ash
Fluid basaltic magma tend to generate 2 types of lavas, called ____ and ____
aa and Pahoehoe
Describe aa flows
surfaces of rough jagged blocks
with dangerously sharp edge
Describe Pahoehoe Flows
smooth surfaces that sometimes resemble twisted braids of ropes
Difference between aa and pahoehoe flows
pahoehoe lavas are hotter and more fluid than aa flows
What is a lava tube
Cave-like tunnels developed by Pahoehoe flows
Describe pillow lavas
Tube-like Structures formed at mid-ocean ridges caused by excessive cooling and break through of magma
Dissolved gasses in magma is called
Volatiles
what are pyroclastic materials
rock and fragments of lava and glass
What are pyroclastic materials also called
Tephra
What is Lapilli
Tephra between 2-64 mm
What is volcanic Ash
Tephra smaller than 2 mm
2 tephra types larger than 64 mm
Volcanic Bombs and Volcanic Blocks
What is a cinder cone
small, steep-sided volcanic landform made primarily of pyroclastic material,
What is a fissure on a volcano
Crack developed by Magma forcing its way up to the surface
what is a conduit on a volcano
Pipe-shaped channel/pipe that carries magma up through a fissure
What is a vent on a volcano
surface opening of the volcano
What are Calderas on a volcano
a large depression formed when a volcano erupts and collapses
What is crater on volcano
bowl-shaped depression or hollow formed at the summit of the volcano created by explosions caused by volcanic activity
Describe Parasitic Cones
flows formed by fissures that develop along the flanks (sides) or at the base of the volcano
What are Fumaroles
Vents on the side of a volcano that only emit gas
Describe Shield Volcanoes
accumulation of fluid basaltic lavas and exhibit the shape of a broad, slightly domed structure that resembles a warrior’s shield
What are seamounts
Underwater volcanoes
Most Shield Volcanoes begin on the Ocean Floor as ______
Seamounts
Largest Shield Volcano
Mauna Loa
What is a composite volcano also called
Stratovolcano
What are Composite Volcanoes
volcanoes with intermediate-felsic composition
Composite Volcanoes are made from what type of magma
Silica-Rich magma
Intermediate Magma generates _____ volcanoes that eject lots of _________
Composite, Pyroclastic
Composite Volcanoes often have ___ slopes
Steep
Shield Volcanoes often have ____ slopes
Gentle
Pyroclastic Flows are Also known as
Nuee Ardentes
What is a pyroclastic flow
a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed
Describe Lahars
Fluid Mudflow caused when volcanic debris becomes saturated with water and rapidly moves down volcanic slopes forming mostly around volcanoes with snow-laden peaks
How can Volcanic Eruptions cause Tsunamis
Collapse of the Volcanic cone can fall into the water, causing a large wave
How do volcanic eruptions affect the atmosphere
volcanoes eject dust-sized particles of volcanic ash and sulfur dioxide gas high into the
atmosphere. The ash particles reflect sunlight back to
space, producing temporary atmospheric cooling
What are Volcanic Necks
roughly cylindrical forms of igneous rock when the magma in volcanic conduit cools after a volcano goes inactive. These can be seen when volcanoes are weathered down.
What are Flood Basalts
Formed when Fissure Eruptions blanket wide areas in basalt.
What are fissure eruptions
when lava eruptions are formed from ridges, or dikes, without a single conduit of lava.
Intrusive Bodies of Magma are also called
Plutons
An intrusion is said to be Discordant if
They cut across existing structures
An intrusion is said to be Concordant if
they inject parallel to features such as sedimentary strata
What is a Dike
discordant bodies that form when magma
is forcibly injected into fractures and cut across bedding surfaces and other structures in the host rock
What is a Sill
nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other rock structures
What are dikes mostly do
serve as tabular conduits that transport magma upward
What are sills mostly do
accumulate magma and increase in thickness
Where do Dikes and Sills usually form
They form close to the surface, where the crust is brittle enough to fracture
Largest intrusive bodies are
Batholiths
Describe a batholith
mammoth linear structures several hundred kilometers long and more than 100 kilometers wide
What is the Difference between Batholiths and Stocks
surface exposure less than 100 square kilometers
What is a Laccolith
igneous rock forcibly injected between sedimentary strata, so as to arch the beds above while leaving those below relatively flat, kind of like a mushroom top.
