Chapter 6
The most peaceful eruptions are __________ eruptions.
Icelandic type
This volcano erupted in 1883 in the Sunda Strait between Sumatra and Java, exploding with a loudness heard 3,000 miles away, then collapsing into its magma chamber, making a caldera and setting off a tsunami that killed at least 36,000 people.
Krakatoa
Some of Earth's most beautiful mountains are ________, including Mt. Kilimanjaro in Tanzania, Mt. Shasta in California, Mt. Rainier in Washington, and Mt. Fuji in Japan.
Stratovolcanoes
__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps.
Stratovolcanoes
The volcanic explosivity index (VEI) measures the size of volcanic eruptions on a scale of 0 to 8. Between 1500 and 1980, one VEI 7 eruption occurred. This was ______________.
Tambora in 1815
Slow flowing, more viscous basaltic lava commonly has a rough, blocky texture called ___________.
aa
A caldera collapse occurs ________________.
after the magma chamber is mostly empty
A mantle hot spot has generated a long-lived plume beneath Yellowstone National Park, and the North American continent is moving __________ above it about 2 to 4 cm/yr.
southwestward
Hawaiian volcanoes unlikely to erupt include _________________.
Diamond Head, Oahu
Mineral growth in magmas at the surface with temperatures around 1,000 to 1,200°C occurs in the following way
- Iron and magnesium will link up with aluminum and the silicon-oxygen tetrahedron as magma temperature decreases to sequentially form four distinct and discontinuous families of minerals—olivine, pyroxene, amphibole, and biotite mica. - Calcium will combine with aluminum and the silicon-oxygen tetrahedron to begin forming the plagioclase feldspar family, a continuous and gradational series of minerals. (Both of these are correct.)
Why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blasts forth violently and deals death over wide areas?
- differences in the chemical and mineral makeup of magmas - variations in the temperature, water and gas content, and viscosity of magmas - different geographic positions with respect to hot spots and edges of tectonic plates (All of these choices are correct.)
The viscosity of magma is lowered by __________.
- increasing temperature - decreasing crystal content - decreasing SiO2 content (All of these choices are correct.)
Rock may melt by _______________.
- lowering the pressure on it - raising its temperature - increasing its water content (All of these choices are correct.)
The typical trend in a rising plume of subduction-zone magma is to increase the ____________.
- percentage of SiO2 - viscosity - explosive potential of the magma by holding in the gases more tightly (All of these choices are correct.)
Spreading centers are an ideal location for volcanism because ______________.
- they sit above the high-temperature asthenosphere - the asthenosphere rock has low percentages of SiO2 - the oceanic plates pull apart causing hot asthenosphere rock to rise and undergo decompression melting to form magma that continues to rise (All of these choices are correct.)
Over _________ % of Earth's magma extruded through volcanism takes place at the oceanic spreading centers.
70%
About _________ % of volcanism is associated with the edges of tectonic plates.
90%
The formation of a giant continental caldera includes all but which of the following?
Basaltic eruptions begin forming circular fractures surrounding the bulge.
Crater Lake, Oregon, fills the caldera of ____________ which collapsed about 7,600 years ago.
Mt. Mazama
On 20 February 1943, a new volcano named __________, a scoria cone, was born when an eruption rose up through a farm field near a village in Mexico.
Paricutin
__________ eruptions are the most violent types of explosive eruptions.
Plinian-type
The most famous of all volcanoes probably is Vesuvius, and the most famous of its eruptions are those of 79 CE, which buried the cities of ____________.
Pompeii and Herculaneum
____________ in the Aegean Sea underwent an explosive series of eruptions around 1628 BCE that buried the Bronze Age city of Akrotiri on Thera to depths of 70 meters.
Santorini
_________ eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions.
Vulcanian-type
A well-formed conical volcano located above an active subduction zone that has not erupted in 12,000 years is __________.
dormant, but will likely erupt again at some point
Most rifting occurs at spreading centers __________.
located below sea level
The presence of water ________ the melting point of rock.
lowers
The number of active "hot spots" on Earth over the last 10 million years active is __________.
more than 100
If basaltic lava reaches the sea or a lake, it cools rapidly into ____________ lava.
pillow
What erupts in a geyser?
superheated water and steam
Silicon and oxygen link up to form the silicon-oxygen ______________.
tetrahedron
What is the cause of volcanism at Italy's Vesuvius, Stromboli, Vulcano, and Etna?
the subduction of Mediterranean seafloor beneath Europe
The three 'Vs' of volcanology are __________________.
viscosity, volatiles, and volume
In magma, __________ is the most abundant dissolved gas.
water vapor (H2O)
A shield volcano has a great ___________.
width compared to its height