EAS Exam 2

Which eruption style is characterized by short lived explosive bursts driven by bursting gas bubbles within magma?

Strombolian

Which eruption type does NOT involve new magma?

Phreatic

Which volcanic product travels as a fast moving mass of hot gas and volcanic matter at ~100 km/h?

Pyroclastic flow

Which volcanic gas is most abundant in magma?

H2O

Which characteristic best describes mafic magma?

Hotter and flows easily

Which eruption type is associated with huge eruption columns reaching into the stratosphere?

Plinian

The Toba eruption (~74,000 years ago) is classified as:

VEI 8

Which of the following settings is typically associated with mantle origin magmas?

Hot spots and divergent boundaries

The geothermal gradient alone is sufficient to melt rocks in the lower crust and upper mantle.

False

A decrease in confining pressure can cause decompression melting.

True

Felsic magma tends to contain more water and gas than mafic magma.

True

Shield volcanoes are typically formed by successive basalt lava flows.

True

Pyroclastic flows are slower than most lava flows.

False

The lateral blast at Mt. St. Helens (1980) removed over 300 meters from the summit.

True

Volcanic aerosols can reach 20 to 25 km altitude and affect global climate.

True

Phreatic eruptions are driven by superheated steam.

True

Cinder cones are typically large stratified volcanoes exceeding 1 km in height.

False

Lake Nyos disaster was caused by sudden release of CO2.

True

Which factors determine the violence of an eruption?

Composition of magma, Temperature of magma, Amount of gases

Which are characteristics of felsic magma?

Higher water and gas content, Cooler temperatures

Which are classified as Plinian or Ultra Plinian examples on the VEI scale?

Yellowstone, Mt. St. Helens, Toba, Long Valley Caldera

Which volcanic hazards contributed significantly to fatalities historically?

Lava flows, Pyroclastic flows, Lahars

Strombolian

An eruption type with short explosive bursts from gas bubble bursting

Vulcanian

An eruption type with short lived explosions ejecting bombs and blocks; more explosive than Strombolian

Phreatic

An eruption type thats steam driven; no new magma

Plinian

An eruption type that’s highly explosive with tall eruption column into stratosphere

Shield Volcano

A volcanic feature that is rounded, low profile with successive basalt flows

Stratovolcano

A volcanic feature that is built by layers of extrusive rock; often explosive

Cinder Cone

A volcanic feature that is cone shaped piles of lapilli and bombs

Caldera

A volcanic feature that collapse after magma chamber drains

What is the VEI classification of the Mt. St. Helens (1980) eruption?

VEI 5

What is the VEI classification of the Mt. Pelée (1902) eruption?

VEI 4

What is the VEI classification of the Tambora (1815) eruption?

VEI 7

What is the VEI classification of the Toba (~74,000 years ago)

  eruption?

VEI 8

Which melting mechanism is illustrated by mantle rock rising upward across the melting curve without additional heat being added?

Decompression melting

Which volcanic setting is most strongly associated with remelting and crustal contamination producing felsic melts?

Continental subduction zone

Which volcanic product is defined by particle size between 2 and 64 mm?

Lapilli

Which eruption style is driven primarily by compression of gas within magma?

Magmatic

Which volcanic hazard caused the majority of fatalities at Mt. Pelée in 1902?

Pyroclastic flow

Which statement best explains why felsic eruptions are often explosive?

High gas content and high viscosity trap gases

Which environment commonly produces pillow basalt?

Deep ocean floor

Which volcanic feature forms after a magma chamber drains and the summit collapses?

Caldera

Decompression melting occurs when pressure increases while temperature stays constant.

False

Felsic magma typically has lower viscosity than mafic magma.

False

Strombolian eruptions can eject lava high into the air in short explosive bursts.

True

Phreatic eruptions involve interaction between magma and water.

True

The VEI scale is a relative scale used to compare eruption size.

True

Basaltic lava commonly forms long-distance flows because it is fluid.

True

Volcanic aerosols from major eruptions can reach the stratosphere.

True

Which are characteristics of shield volcanoes?

Steep symmetrical cone with alternating ash layers, Rounded, low profile, Built from successive basalt flows

Which hazards are directly associated with explosive felsic eruptions?

Pyroclastic flows, Lahars, High eruption columns

Decompression melting

A melting mechanism that drops in confining pressure as rock ascends

Flux melting

A melting mechanism where the addition of water lowers melting temperature

Additional heat

A melting mechanism that is friction in subduction zone or rising hot mantle

Strombolian

A type of eruption with

Vulcanian

A type of eruption with short lived explosions ejecting bombs and blocks

Plinian

A type of eruption with massive column reaching into stratosphere

Phreatic

A type of eruption with

What event, triggered after a volcanic eruption, causes the most casualties? 

Pyroclastic debris flow

Nonviolent eruptions characterized by extensive flows of basaltic lava are termed __________.

Effusive

Which of the following determines how violent an eruption will be?

Magma composition, Magma temperature, Amount of gas in the magma

Choose the following that correctly describes a mafic magma/lava as compared to a felsic magma/lava.

Higher magma/lava temperature, Lower gas content, Likely to produce basalt, Common at divergent boundaries, Lower silica content

Magmatic eruptions can be effusive and explosive.

True

Which of the following does not correctly describe a felsic magma/lava?

higher temperature as compared to mafic

Mt. St Helens is a _______ and the eruption in 1980 was_______.

stratovolcano; explosive

What volcanic eruption was the largest to occur in our historical records, where impacts included economic collapse, art and literature influences, and global pandemics?

Tambora

What statement best describes the Catastrophe Theory?

The volcanic eruption was thought to have killed most of the homo sapiens species, causing a genetic bottle neck.

Which statement best describes relative dating?

Determining the order of geologic events using logic

Which principle states that sedimentary layers are originally deposited horizontally?

Principle of Original Horizontality

Which relative dating principle states that fragments inside a rock must be older than the rock containing them?

Inclusions

Which feature must be younger than the rock it cuts across?

Fault

Which unconformity represents missing time between horizontal sedimentary layers?

Disconformity

Which unconformity forms when younger sediment overlies tilted or folded older strata?

Angular Unconformity

Which unconformity forms when sedimentary rock overlies igneous or metamorphic rock?

Nonconformity

Which of the following is required for accurate radiometric dating?

A closed system

Which instrument is used to measure parent and daughter isotopes?

Mass spectrometer

Which isotope is useful for dating very recent events?

Carbon-14

Which statement is correct?

• Absolute dating determines the relative order of rocks

• Relative dating yields numerical ages

• Radiometric dating yields numerical ages

• Cross-cutting relationships apply only to sedimentary rocks

Radiometric dating yields numerical ages

Which statement is correct?

• Daughter isotopes decay into parent isotopes

• Parent isotopes decay into daughter isotopes

• Isotopes always have identical numbers of neutrons

• All isotopes are radioactive

Parent isotopes decay into daughter isotopes

The Law of Superposition states that the youngest rocks are found at the bottom of an undisturbed sequence.

False

The Principle of Lateral Continuity states that sedimentary layers extend laterally when deposited.

True

Radiometric dating measures the ratio of parent to daughter isotopes.

True

Carbon-14 has a half-life of 5730 years.

True

Baked contacts indicate that the baked rock is younger than the intrusion.

False

The Principle of Faunal Succession states that fossils occur in a predictable vertical order.

True

Radiocarbon dating can be used to date rocks billions of years old.

False

An angular unconformity represents a gap in time.

True

Law of Superposition

oldest layers on bottom, youngest on top

Cross-Cutting Relationships

Feature that cuts across another is younger

Inclusions

Fragments inside a rock are older than the host rock

Faunal Succession

Fossils succeed each other vertically in a predictable order

Disconformity

Horizontal sedimentary layers separated by erosional surface

Angular unconformity

Tilted older layers overlain by horizontal younger layers

Nonconformity

sedimentary rocks overlie igneous or metamorphic rocks

Parent isotope

Original radioactive atom

Daughter isotope

Product of radioactive decay

Half-life

time required for half of radioactive atoms to decay

Isotope

Atom with same number of protons but different neutrons

Which term refers to measuring when a geologic event occurred in exact units of time?

Absolute (radiometric) dating

Which principle states that sedimentary layers extend laterally in all directions when deposited?

Principle of Lateral Continuity