Exam II UPDATED

Volcanoes

Openings or vents where lava, tephra, and steam erupt onto Earth's surface.

Hunga Tonga -- Hunga Ha'apai (2022)

The largest eruption in the 21st century, based on the height of the eruptive cloud and volume of material erupted.

Mid-Ocean Ridge Volcanism

Volcanism occurring at plate divergence boundaries (such as the Mid-Atlantic Ridge or Iceland) characterized by basaltic and mafic melts.

Mafic Melts

Melts formed by the partial melting of the ultra-mafic mantle, resulting in gentle eruptions.

Hot-Spot Volcanism

Volcanism occurring independently of plate boundaries, such as in Volcanoes National Park in Hawaii.

Arc Volcanism

Continental margin volcanism, such as at Mt. Rainier, Washington, driven by continental plate subduction and characterized by felsic melts.

Felsic Melts

Melts formed by re-melting and contamination by the crust, resulting in explosive eruptions.

Formation of a Caldera

Filling of a magma chamber triggers an eruption from central/flank vents, causing the summit to collapse as the chamber drains, which then fills with water and allows new volcanic dome growth.

Crater Lake, Oregon

A famous caldera example where the collapsed region filled with water and Wizard Island grew as a small volcano on the floor.

Volcanic Monitoring Methods

Deformation, gas emission, ground deformation, and remote sensing.

Geothermal Gradient

Earth's natural temperature increase with depth, which alone is not sufficient to melt typical rocks at the lower crust and upper mantle without additional factors.

Additional Heat Sources for Melting Rocks

Friction in subduction zones and rising, hot mantle rocks.

Decompression Melting

Melting caused by a drop in confining pressure as hot rock ascends, which lowers the melting temperature.

Volatiles in Volcanism

Substances (primarily water) released from descending crust that lower the melting temperature of the overlying asthenosphere.

Mafic Magma Characteristics

Less silica (1-2%), hotter temperature, lower viscosity, lower water and gas content, and less explosive behavior.

Felsic Magma Characteristics

More silica (4-6%), cooler temperature, higher viscosity, higher water and gas content, and greater explosiveness.

Shield Volcano

An effusive, rounded volcano with a low profile formed from successive fluid basalt lava flows (e.g., Mauna Loa and Kilauea).

Icelandic & Fissure Volcanoes

Effusive eruptions through fractures in the Earth's crust that spew fluid, low-viscosity basaltic lava.

Pillow Basalt

Effusive volcanic structures formed primarily along mid-ocean ridges and oceanic hotspots underwater, caused by eruption of basalt underwater

Stratovolcano

An explosive volcano built by successive layers of extrusive rock, forming high peaks with more viscous, less fluid magma (e.g., Mt. St. Helens).

Cinder Cones

Explosive, relatively small (<300 m) cone-shaped piles of lapilli and bombs with straight sides and steep slopes, often on the flanks of larger volcanoes (e.g., SP Crater Arizona, Cerro Negro Nicaragua).

Strombolian Eruptions

Explosive eruptions driven by the bursting of gas bubbles within intermediate-viscosity magma, characterized by short-lived ejections high into the air (e.g., Stromboli, Italy).

Vulcanian Eruptions

Explosive eruptions featuring viscous intermediate magma that traps gases, leading to short-lived explosions lasting minutes to hours, ejecting bombs/blocks with a higher eruptive column than Strombolian.

Phreatic Eruptions

Explosive eruptions driven by heat from magma interacting with water (groundwater, hydrothermal systems, surface runoff, lakes, or sea) that pulverize surrounding rocks into ash without producing new magma.

Plinian Eruptions

Huge explosive eruptions with massive amounts of debris and hot gases ejected high into the stratosphere, generating fast-moving pyroclastic flows moving around 100 km/hr (e.g., Toba, Tambora, Crater Lake, Yellowstone, Vesuvius, Mt. St. Helens).

Pelean Eruptions

Eruptions where large quantities of gas, dust, ash, and lava are blown out of a central crater, falling back and traveling down the volcano’s side at tremendous speeds as glowing avalanches (e.g. Mt Pelee)

Toba Supervolcano Eruption

VEI 8 supervolcano eruption in Indonesia that erupted 100 times more material than Tambora

Tambora Eruption (April 1815)

An eruption producing a large blast, pyroclastic flows, and tsunamis with a 28-mile-high column, killing 10,000 islands directly and 80,000 mroe due to indirect effects. Material ejection lead to 1816 “Year without winter,” due to its cooling effect.

Krakatoa Eruption

Loudest eruption ever, loudest acoustic sound ever recorded

Mt St Helens Eruption (1980)

1980 lateral blast volcano in Washing State removed 396 m of volcano, destroyed millions in timber, devastated 596 km of land, killed 57 people, and marked the deadliest/most economically destructive volcanic event in US history

Factors Determining Eruption Violence

Composition, temperature, and amount of gases in magma

Effusive vs. Explosive Eruptions

Effusive eruptions feature long-distance lava flows and gas emissions while explosive eruptions feature ash, pyroclastic flows, lahars, tsunamis, and climate change effects

Basaltic/Mafic Lava Flow Properties

Thin and fluid, rapid speeds (up to 30 km/hr), long distances (10-100 km), common at hot spots and divergent boundaries (e. g. Hawaii)

Rhyolitic/Felsic Lava Flow Properties

Viscous, plugs the vent as a lava dome, builds pressure leading to explosive eruptions, common at ocean-continent subduction zones (e.g. Novarupta, Alaska)

Size Classes of Tephra

Fine ash (< 2 mm) lapilli (2-64 mm), and blocks and bombs (> 64 mm)

Volcanic Gas Components

Comprises of 1 to 9% magma: water (most abundant), CO2 (2nd in abundance), and SO2 (Reacts with water to form aerosol sulfuric acid, which leads to cooling)

Metamorphism

Collection of solid-state processes such as temperature, pressure, or fluids that modify a rock (protolith) without melting

Shock Metamorphism

Impact-driven ultra-high pressure squeezes rock, caused by meteors

Burial Metamorphism

High pressure and temperature change rock due to deep burial in sedimentary basins or prisms

Contact Metamorphism

High temperatures bake rock adjacent to hot magma bodies

Compression and Shear Metamorphism

Horizontal compression and parallel stress (Shear) lead to recrystallization and foliation

Hydrothermal Metamorphism

Hot fluids allow the transport and precipitation of dissolved minerals, altering rock chemistry

Blue Schist and Eclogite Metamorphism

Metamorphic rock assemblages that form an accretionary prism, common at subduction boundaries (high-pressure, low temperatures)

Structural Changes during Metamorphism

Recrystallization, phase change, neo crystallization, pressure solution, and plastic deformation

Recrystallization

The change in size and shape of mineral grains without changing the mineral chemistry

Phase Change

The repacking of atoms into new crystal structures under changing pressure & temperature

Neo Crystallization

Growth of entirely new minerals that were not present in the original protolith

Pressure Solution

Mineral grains dissolve where directed stress is highest in the presence of pore liquid, migrating and reprecipitating elsewhere

Plastic Deformation

Mineral grains are squeezed or sheared into flattened or elongated shapes at high temperatures without breaking

Causes of Foliation

Parallel planar surfaces or layers formed by the alignment of grains and banding of different minerals

Metamorphic Intensity Trend

As intensity of metamorphism increases, so does crystal size and foliation grade (slate, phyllite, schist, gneiss)

Protoliths

Shale → Slate, Sandstone → Quartz, Limestone → Marble, Granite → Gneiss, Conglomerate → Meta conglomerate, bituminous coal → anthracite coal

Controls on Metamorphic Mineral Assemblance

Pressure and temperature, composition of fluid present, & bulk composition of rock

Radiometric Dating

A technique measuring when geologic event occurred in exact units of time through radioactive isotopes

Parent & Daughter Atoms

Parent is the original radioactive isotope atom → Daughter is the stable new form of atom resulting from decay

Half-Life

The amount of time it takes for 50% of the original number of radioactive parent atoms to decay

Carbon-14 Dating

A dating method used for very recent events since Carbon-14 has a short short-life of only 5730 years, where atmospheric C14 is absorbed by living matter

Radiometric Age Calculation Formula

Age = Number of Half-lives elapsed x Half life duration

Stratigraphy

The branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale

Law of Superposition

Undisturbed sequence places bottom layers as oldest

Principle of Original Horizontality

Layers settle flat due to gravity initially

Three Rock Sets of Grand Canyon

1. Layered Paleozoic Rocks: sedimentary canyon walls

2. Supergroup Rocks: sedimentary & volcanic layers bounded by unconformities

3. Vishnu Basement Rocks: ancient metamorphic/igneous rocks like Zoroaster Granite & Vishnu Schist

Principle of Inclusions

Enclosed fragments are older than host rock

Principle of Lateral Continuity

When deposited, layers of sediment will extend laterally in all directions until they thin out or terminate against an edge

Baked Contacts Principle

An igneous intrusion will bake surrounding rocks, meaning the rock being baked must be older than the intrusion

Principle of Faunal Succession

Fossil assemblages change in a consistent chronological order

Disconformity

An unconformity representing missing time between horizontal sedimentary layers

Angular Unconformity

Gap where underlying strata are tilted at an angle to overlying strata

Nonconformity

Unconformity between older igneous or metamorphic rocks and younger overlying sedimentary rocks

Geological Time Hierarchy

Broken down from largest to smallest into Eons, Eras, Periods, Epochs, and Ages

Period

Time it takes for rock to form

Current Geological Time

Phanerozoic Eon, Cenozoic Era, Quaternary Period, and Holocene Epoch

Age of Earth

4.6 billion years old

Precambrian Duration

88% of Earth’s history

Hadean Eon Earth

Initially rich in hydrogen and helium; early Earth in a molten state due to atmospheric ammonia, methane, and CO2; warm atmosphere

Moon Formation Daughter Hypothesis & Problem

Hypothesis that moon was pulled out of Earth, leaving Pacific Ocean basin, but requires Earth to spin too fast

Archean Eon Crustal Growth

Significant time for continental crust growth, 80% of continental crust formed

Banded Iron Formation

Interlayered alternating chert and iron oxide deposits whose formation indicates there was little free oxygen available in the atmosphere

Paleoproterozoic Rise in Oxygen

Driven by evolution of photosynthetic algae and cyanobacteria developing ability to photosynthesize

Stromatolites

Finely layered, mound-shaped accumulations of mud trapped by mats of blue-green algae

Great Oxidation Event

Introduction of significant free oxygen into the atmosphere caused by increased O₂ sources, mantle oxidation, and a switch to subaerial volcanoes due to thick continental crust

Evidence of Great Oxidation Event

First appearance on continental margins of red sandstones and iron-rich paleosols, so soil iron was oxidized

Formation of Ozone Shield

As atmosphere O₂, the ozone layer accumulated via interaction of UV radiation and O₂, absorbing harmful UV

Snowball Earth

Hypothesis that Earth’s surface became entirely or nearly entirely frozen during proterozoic

Causes of Snowball Earth

Breakup of supercontinent Rodinia in tropical locations led to increased weathering, pulling down CO2 and lowering greenhouse effect + albedo feedback from volcanic aerosols and expanding ice relecting sunlight

Evidence for Snowball Earth

Peak in banded iron formations exclusively in marina strata indicated widespread anoxia, consistent with ice-covered ocean

End of Snowball Earth

Volcanic activity and CO₂ production continued during the icehouse event and with ice covering weathering surfacing, nothing took CO2 out of the atmosphere, massively enhancing the greenhouse effect

Ediacaran Fauna

Earliest known evidence of biological activity became stable due to sufficient oxygen following initial appearance of first multicellular organisms

Paleozoic Era

Marked by an explosion of life, including life-forms with hard parts such as shells

Cambrian Period Marine LIfe

Thrived in warm waters, including trilobites and brachiopods

Permian Extinction

Mass extinction at the close of the Paleozoic that destroyed 70% of land species and 90% of all marine life, caused by nutrient cycle disruption, large impact, and increased volcanism

Carboniferous Period Environment

Warm-climates with world-covering swamps that created major coal deposits, first land-adapted vertebrates, and an increase in insect diversity (like winged insects)

East Coast Tectonics in Paleozoic

Resulted in the formation of the Appalachian Mountains

Mesozoic Era

Era where reptiles became dominant animals with no major glacial events, much of the land above sea level, and sea levels rising into western North America due to warm climate and fast plate spreading

Sevier Orogeny

Subduction of the Farallon plate created mountains from Canada to Mexico via thin-skinned deformation, with older faults in the West and younger in the East

Laramide Orogeny

Continued subduction of the Farallon plate featuring thick-skinned deformation and flat-subduction, leading to a mountain creation further East like the Rocky Mountains

K-P Extinction Event

Extinction event that killed the dinosaurs, resulting from a major asteroid impact and subsequent severe climatic impacts

Cenozoic Era

Era where mammals replaced reptiles as dominant as dominant land vertebrates, featuring marsupials and placentals

Late Pleistocene Megafauna Extinctions

Eliminated larger animals due to climate changes affecting food chains, human overkill, and forest fires altering climate

Trap Cave, Wyoming

A Pleistocene fossil-rich cave in Wyoming where ~30,000 specimens (such as pack rats) fell in and died, used to model how species became fossilized and understand extinction events