Geology Exam 1

Lectures 1-8b

When did Mount St. Helens erupt

May 18, 1980

Subduction zones make what type of volcanos

Stratovolcanoes

Which of the following are pyroclastic rocks (choose all that apply)?

Pumice, scoria, and tuff

When was Mount st. helens national volcanic monument established and where is it

1982, in WA’s Gifford Pinchot National Forest

History of Mt St Helens

40-50,000 yrs of eruptive history. Alternate between eruptive growth and dormant weathering and decay. 4 major eruptive phases with the most recent being 3,900 yrs ago

Warning signs of Mt St Helens eruption

1 after 123 yrs of dormant, 4.1 earthquake. 2 harmonic tremors (low magnitutude earthquakes). 3 Phreatic (steam) eruptions 4 North flank started bulging rapidly.

North Flank Bulge - growth and collapse

GROWTH grow at 2m/day. 1.5km accross and 100m high. COLLAPSE facture at summit signaled may collapse. 5.1 earthquake on the 18th made the N flank fail - giant debri avalanch at speed 200km/hr and 2.5km³ of material. collapse removed structural support above magma chammber exposing it, magma relesed gas - bubbles - explostion.

Lateral Blast (Speed, Temp, Distance)

speed 500km/hr, temp 300C distance 600km²

Upward blast (How much ash up, Distance up in time, how long entire eruption, wich direction ash, where did laharas go)

1.3 km³ ash into air, 25km into atmosphere in 15 min, 9hrs of eruption, wind blew ash eastward, laharas eventualy reached columbia river

Aftermath - how much removed, shape, how many ppl died

Removed 400m from summit, North facing amphetheater shape, 57 ppl died

how long ago was the first life on earth

550 ma (biological big bang, NOT humans yet)

list the eras of geologic time

[old] Paleozoic, Mesozoic (dinos), Cenozoic (ppl at end) [new]

if earths history put on a yr long scale, what would we see

First mineral early January, Biological Big Bang November, giant extinction early December, dinos early ish December, humans very end of December.

When and where did the Yellowstone hotspot begin

16ma in Oregon

how many caldera forming eruptions have occurred in present day yellowstone

3

How many hydrothermal features in Yellowstone

over 10,000

How many volcanos are on Hawai’i and which ones are in the national park?

5, Mauna Loa and Kilauea

What is Manau Loa’s elevation

13,679 at sea level or 32,000 from ocean floor

how tall were the lava fountains of Kilauea’s last eruptive phase in January 2026

1,500 ft tall

When did Mauna Loa last erupt?

2022

Which type of lava is rubbly vs smooth

A’a is rubbly, Pahoehoe is smooth

What is a Hotspot

A thermal upwelling of magma (mantle wells up → decomposes → melts → basalt) (crustal rock → melts → explosive Rhyolite). a hotspot happens when magma comes up in middle of plate. It stays in one spot, but the plate moves over it creating a trail of eruptions.

What is a caldera

volcanic feature that collapsed cuz of withdrawal of magma. 1km or more in width.

Explain Pyroclastic Density Currents (PDCs)

A caldera-forming eruption lets of a hot cloud of ash, rock, and gas - a PDC. PDCs deposit onto ground either welded (called Tuffs) or unwelded. Tuffs have no layers and are in big deposits. the most recent was lava creek 640ka.

When was the most recent caldera forming eruption

lava creek, 640ka

what is huckleberry ridge

Biggest Yellowstone eruption, 2.1ma, 185m thick tuff.

what formed the trenches and canyons of yellowstone

giant ice cap melt 15ka

What makes a hydrothermal feature

rain goes down, heat+fluid+rock mix under lightly molten magma chamber 5km below yellowstone, then come up as a hydrothermal feature

Mammoth Hot springs

Cools into shelves of travertine

Grand Prismatic Spring

Rim has thermophilic microbial organisms making it a pretty color

What is VEI scale

Volcanic Explosivity Index (VEI), a logarithmic scale from 0 to 8. the Lava Creek and Huckleberry Ridge eruptions were VEI 8 ("mega-colossal"), which classifies them as "supervolcanoes" (defined as ejecting over 1000 km³ of material)

Explain how Old Faithful works

Water in rocks is hot and has a lot of pressure. It flashes into steam and erupts.

What are mudpots and fumarols

Mudpots are water and clay, fumarols are steam and gas (from the degassing of magma chamber below)

How many species of wildlife are in yellowstone and what are the main ones

67; Bison, elk, Grizzley bears, and wolves

When was Yellowstone Est.

1872

When was Hawaiʻi Volcanoes National Park Est.

1916

What type of volcanos are on Hawai’i?

5 sheild volcanos - Tall and wide with low elevation gradients at areas with sustained production and low viscosity mafic magma.

List the 5 volcanos, their activity status, and when they last erupted.

Kilauea - active, Dec 23 2026

Mauna Loa - Quiescent, 2022

Hualalai - Quiescent, 1801

Mauna Kea - Dormant, 2460 BCE

Kohala - Extinct, last 60,000 yrs.

What are lava tubes

Lava tubes form when magma flows beneath an insulated crust; when the lava drains away, it leaves behind hollow cave systems.

how long ago did the Hawaiian-Emperor Seamount Chain start

The Hawaiian-Emperor Seamount Chain stretches back at least 64.7 million years to the Aleutian Trench

What are Xenoliths

Erupting basalts sometimes carry "xenoliths"—solid chunks of green olivine eroded from the Earth's mantle—giving geologists a rare window into Earth's deep interior

What are Tumuli

mounds formed when the brittle crust of a pahoehoe flow is inflated upward by the pressure of the flowing lava beneath it

What are lavacicles

drip-like pendants hanging from the ceiling of lava tubes

How many parks

63

First federal reserved land

Yosemite

Forest reserve act of 1891

president can now make forest reserves (national forests

Jackson Hole Controversy

John D. Rockefeller bought land in Wy, made Tetons national monument, abolished, veto, but antiquities no longer apply.

Acts of 1964

Land and water conservation, wilderness, and national trails system, Wild and scenic rivers (1968)

1971 Alaska Native Claims Settlement Act (ANCSA)

Temporarily conserved for future NPS additions, 32 Million acres

National parks and recreation act of 1978

preserve natural and cultural heritage

Alaska National Interest Land Conservation Act of 1980

Jimmy Carter, 7 National parks, 5000 acres of protected land in Alaska, no more antiquites act.

NPS director

Jessica Bowlin, MABA, balance environmental stewardship and economic growth and recreation.

CA desert protection act of 1994

new wilderness, different rules for native Americans

1st National Park

Yellowstone

1906 Antiquities act

president can make national monuments, ntl mons by DOI and A and W, Ntl parks by DOI

1916 National Park Service act

All ntl mons by nps (within DOI), led by marthur and albright

First president to use antiquates

President Theodore Roosevelt was the first to use the Antiquities Act, declaring 18 national monuments, including Devils Tower

Age of earth

4.6ga

Thickness of each layer

Crust (7-70km), Mantle (70-2900km), Liquid Core (2890-5150km, know liquid cuz s waves dont pass), Solid Core (5150-6370km). AS DEPTH -, TEMP (geotherm) and DENSITY and PRESURE +.

What elements are 99% of earths mass

Fe, Si, O, Mg, Al, Ca, Ni, S

Crust Density

Continental (2.8g/cm³, 35-40km thick) ← average. Oceanic (3.0g/cm³, 7km) ← Pretty constant.

Define MOHO

The Mohorovičić Discontinuity (Moho) is the boundary that separates the crust from the underlying mantle. thicker under continental crust.

Lithosphere

Crust and solid upper mantle, 100km, has tectonic plates, brittle

Asthenosphere

Soft upper mantle under Lithosphere, 300km

Outer Core elements and density

Mostly Fe, some Ni, S, and O. Liquid. 11g/cm³

Inner Core elements and density

Mostly Fe, some Ni. Solid (cuz of pressure). 13g/cm³

What element is more in crust than any other part of the earth

Silicon

what layer makes up most of the earths volume and what is its density

Mantle, 3.4g/cm³

Between what layers is the biggest jump in density

the core-mantle boundary

What are the cascades?

1,100 km volcanic chain parallel to the pacific NW coast. 13 active volcanos including Mt. Saint Hellens (erupted in 1980, 57 fatalities).

What is the highest mountain in the cascades

Mt. Rainier, then Mt. Shasta.

What created the Volcanic Chain of the cascades?

The volcanic chain exists because of the Cascadia Subduction Zone, a convergent boundary where the Juan de Fuca, Gorda, and Explorer oceanic plates subduct beneath the North American plate. Converge at 4cm/yr

How is magma produced for the cascades

The Juan de Fuca plate is spreading, releasing magma in the middle. The Juan de Fuca plate subducts under the North American plate, bringing water with it (pressure induced dehydration of the subducting plate). that water lowers the melting point of the mantle above, so it melts into a viscus, silica-rich magma with dissolved gasses/volatiles that rises to the surface.

what is the relationship between silica and explosiveness

More silica = more viscous (thick) magma = trap more gas = more explosive eruption.

[Runny] Basalt → Andesite → Dacite → Rhyolite [Viscous]

How do we determine risk of volcano

Look at history, magma chemistry, and geology

How do pyroclastic eruptions happen

Rappic gas expansion can shatter magma into Tephra (ash and pumice) which can be microscopic or large chunks. (the ash is hard (glass and rock), (The pumice is porous, low-density volcanic glass that builds up into stratovolcanoes).

How many eruptions in the 4,000 years?

11/13 volcanoes have erupted in last 4,000 years.

what are laharas

The high elevations of stratovolcanoes so covered in snow and glacial ice, which can melt during eruptions to create destructive mudflows called lahars

Define mineral

Natural, inorganic, crystalline, definite homogeneous chemical composition.

how much of the crust are made up of silicates

92% (feldspars are most common group)

Intrusive Igneous Rocks

Slow formation, deep, big crystals

Extrusive Igneous Rocks

Rapid formation, surface, small crystals, explode outa volcanos

how are sedimentary rocks formed

Weathering → erosion → Transportation → Deposition → burial → Lithification

what percent of the immediate surface is sedimentary rocks

80%

Clastic rocks

Sedimentary, rock fragmants (ex. sandstone or shale)

Chemical/biogenic

precipitation or carbon from biological processes (ex. like limestone or halite)

conditions of forming metamorphic rocks

solid-state recrystallization at 10km deep and temp 200-800 degrees Celsius. Does not completely melt.

Regional Metamorphic Rocks

High T+P, Foliation (layers), mountains, ex gneiss, schist.

Contact Metamorphic Rocks

High Temp from nearby magmatic intrusions, ex. marble.

How are minerals formed?

crystallization from a liquid (melting), diffusion from solid, precipitation of water (a solution), weathering, crystallization from a gas, and biomineralization. (NOT elastic strain or organic mater)

What type of rocks to igneous rocks involved in mountain building turn into?

Metamorphic

Define cleavage

tendency of minerals to break in persistent planes. NOT in all minerals.

List igneous rock composition categories and give examples.

[DARKEST] Ultra Mafic (Peridotite+Kimberlite) Mafic (Basalt+Gabbro) Intermediate (Diorite+Adesite) Felsic (Granite+Rhyolite) [LIGHTEST]

what is the CO gemstone

Aquamarine (blue)

What is the CO mineral

Rhodochrosit (red)

How is ore formed

Many ores form in hydrothermal veins, where hot water descending into fractures is heated by magma and ascends, depositing sulfides, silicates, and native elements like gold and silver

what are placer deposits

Placer deposits are concentrations of heavy minerals (like gold) in stream beds, which were heavily targeted during early mining history like panning in the Platte River

What chemicals make it blue

Iron and Titanium

What chemical makes it red

Chromium