Unit 12 Final
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What are some of the causes of heat within the interior of the Earth?
- Impacts of of meteorite.
- Compression caused by gravity of thousands of miles of overlying rock layers.
- Heat generated by radioactive decay of elements in Earth's mantle and core.
Describe the origin of the Earth's moon.
Our moon is the product of collision between a Mars-sized planet and early Earth
What is the difference between magma and lava?
Magma is molten rock below the Earth's surface. Lava is molten rock above the Earth's surface.
What is the difference between and intrusive igneous rock and an extrusive igneous rock?
- Extrusive igneous rocks form from magma that solidifies after reaching the surface of the Earth. Gas bubbles are commonly found within this type of rock.
- Intrusive rocks form from magma that solidified below the Earth's surface. Slow cooling produces large mineral crystals while quicker cooling forms smaller crystals.
Why would magma have a tendency to rise towards the Earth's surface?
Magma is less dense (lighter) than its solid rock phase because its molecules are further apart. This lower density will cause the magma to rise toward the surface (like the salt domes).
What is the geothermal gradient?
It represents the increase in temperature with depth into the Earth.
What is geopressure?
Increase of pressure with depth into the Earth.
Where are most natural diamonds created?
With which geologic feature do diamonds get to the Earth's surface?
Diamonds are brought to the Earth's surface by "kimberlite pipes" (a special type of explosive volcano).
We say we can get a lava flow with partial melting. What is partial melting?
Only 10%-20% of minerals melting are needed to produce a fluid magma.
What two methods can reduce a rock's melting temperature within the Earth?
- For convergent (subduction zones):
- Decreasing the pressure on hot solid rock BY FRACTURES (pressure relief melting) will lower the normal melting point of a mineral which can result in a magma. (Used a pressure cooker as an example.)
- Adding water to hot solid rock can lowr the normal melting point of a rock which can result in a magma.
- Divergent or rift zone:
- The hot crust will rise and fracture.
- The fracturing decreases the pressure on the hot rock which in turn will lower the normal melting point of a mineral which finally produces a magma (pressure relief melting).
What gas is most common (about 70%) within magmas?
Water vapor (a green house gas).
Which gas is the second most common from volcanoes (about 20%)?
Carbon dioxide (a greenhouse gas).
What can happen if too much carbon dioxide accumulates in a deep volcano lake?
Carbon dioxide can also be deadly when first accumulated at the bottom of volcanic lakes-then expelled.
What can be the effect of acid gasses on scoria?
Acid can "alter" black scoria rocks into red scoria rocks.
In which tectonic environments are igneous rocks created?
- Tectonic divergent plate boundaries (mid-oceanic ridges and continental rifts).
- Tectonic convergent plate boundaries.
- Mantle plumes or hotpsots that rise from Earth's liquid iron core.
Which two minerals are most common in convergent zones and continental crusts?
- Quartz and oroclase.
- Sand and ooze.
What type of magma do convergent usually produce?
Felsic or silicic magma.
What type of magma do divergent zones and hot spots usually produce?
Compare the violence of eruptions with felsic and mafic magmas.
- Felsic: assocaiated with intense, explosive volcanic activity.
- Mafic: volcanic activity is relatively quiet compared to felsic volcanoes
Compare the viscosity of felsic and mafic magmas.
- Felsic. The greater the content, the greater the viscosity of a lava, the slower the lava will flow.
- Mafic: Formed in very liquid-like lavas which can flow almost like water (very low viscosity).
What is a pyroclastic?
Solid material (igneous rock) blown from a volcano during and explosive eruption.
What is a volcanic ash and describe some of its effects on people.
Volcanic dust represented by tiny, sharp-edged dust particles violently ejected from volcanoes (dangerous to inhale in large quantities).
What is the source of South Texas uranium deposits?
What is the volcanic bomb?
Volcanic rocks that are larger than gravel size and are tapered from passage through air (while still molten).
What is Pele's hair?
Volcanic fibers that are long, glassy fibers of igneous rock produced from volcanic explosions. Pele's tears are small tear-shaped particles associated with volcanic fibers.
Compare pahoehoe with "aa" lava rock.
- Pahoehoe: rock formed by "fast-flowing" lava (typically has a ropy crust.
- Aa: jagged, sharp-edged rock formed by relatively slow-moving, very viscous lava.
What type of lava is produced when lava is extended under water?
Pillow lava (pillow basalts).
About how many surface volcanoes have been active since historic times?
550 active volcanoes.
Why is it that a basalt volcano usually does not form steep cones?
Basalt lavas can flow like water down the volcano slope, making it almost impossible to build up a steep cone; shaped like a very broad dome.
Where might you find small shield volcanoes near Corpus Christi?
In a belt that extends from Uvalde TX to Austin TX.
What effect did the Indonesian volcano of Mt. Toba have on humans?
Almost destroyed the human race. It ejected more than 670 cubic miles of volcanic ash around the world. The resultant caldera is 65 miles long and 25 miles wide.
Which volcanoes are associated with pyroclastic clouds?
- Eruption in 1996 Montesseart.
- Mt. Pinatubo of the Philippines.
- Mt. Vesuvius in Pompeii, Italy.
- Mt. St. Helens in Washington State.
How do we know that people were living in Pompeii when it was covered with pyroclastic cloud?
Today we find human molds of victims that were caught up and enveloped by the flow.
With which two methods can a cadera be formed?
- By a volcano eruption.
- By magma exiting the side of the volcano.
Which class of volcanoes are associated with pyrcoclastic clouds?
What makes Yellowstone dangerous (in regards to volcanoes)?
Yellowstone have had three massive eruption, each about 200,000 years apart. The last one occurred more than 200,000 years ago. Yellowstone sits over a large pool of deep magma that is causing the area to rise and fall. Some are predicting another super volcano explosion.
What are flood basalts?
- Mafic, continous massive flows of basalt from fautl zone.
- Mafic magma can be extruded from very long cracks or fissures to "flood vast areas with basalt" thus the term flood basalts.
What is a volcanic neck?
An eroded volcanic cone with the remaining intrusive exposed.
Identify a picture of columnar jointing.
- Columns of rock created by polygonal cracks (contraction by cooling) found in mafic volcanic necks and in many mafic flows (sometimes can be found with silicic flows).
From a sketch, be able to identify a batholith, dike, or sill
What is the name of a famous Texas 1.1 billion year old batholith?
Enchanted Rock, west of Austin, near Fredricksburg.
Where do we find the largest known volcano in our solar system?
Olympus Mons on Mars, at more than 66,000 feet high.
Which of Jupiter's moons have active volcanoes?
What made Paricutin famous?
- Grew from a crack in a cornfield to a large killer volcano in Mexico in 1943.
- In 1949, a pyroclastic cloud from that volcano killed more than 1,000 locals attending a fiesta.
What caused the "volcano" near Taft, TX?
Result of a gas well blowout that caught fire in 1939.
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