Geology and Volcanoes: Key Concepts for Students

If you were hiking on a Hawaiian volcano and picked up a rock, you would most likely be able to describe it as what?

Basalt

Bridalveil Fall is approximately how tall and is across the valley from what major rock monolith?

~620 feet; El Capitan

How could you determine if a basalt layer between sedimentary layers is a lava flow or a sill?

Lava flow bakes below; sill bakes above and below

Why are there so many active volcanoes in the Cascade Mountains?

Subduction of the Juan de Fuca Plate

Ash and dust, lapilli or cinders, and blocks and bombs are all types of what?

Tephra

What types of rocks would you likely observe at Mount Rainier National Park?

Andesite, dacite, basalt

What feature is responsible for volcanism at Yellowstone National Park?

Mantle hotspot

How do volcanoes at Hawaii differ from those at Mount Rainier and Yellowstone?

Hawaii: basaltic shields; Rainier: stratovolcano; Yellowstone: rhyolitic caldera

When large volumes of magma erupt quickly, the rock above collapses leaving what feature?

Caldera

What type of volcano was Mount Tehama?

Stratovolcano

What is exfoliation jointing and how does it form?

Sheet-like fractures from pressure release

Which basaltic lava flow has a smooth, ropy surface?

Pāhoehoe

How does water affect the melting temperature of silicates?

Lowers melting temperature

Which Yellowstone thermal feature precipitates carbonate?

Mammoth Hot Springs

What submarine volcano is forming southeast of the Big Island of Hawaii?

Kamaʻehuakanaloa (Lōʻihi)

What is Wizard Island and when did it form relative to Mount Mazama?

Cinder cone formed after collapse

What is the difference between Bumpass Hell and Devil's Backbone?

Hydrothermal area vs lava spine

What are the Royal Arches and how did they form?

Granite arches from exfoliation

Differences between shield and composite volcanoes are primarily due to what?

Magma viscosity and composition

Which minerals crystallize first as magma cools?

Olivine and calcium-rich plagioclase

What is the longest, lowest-terminus glacier in the contiguous U.S.?

Emmons Glacier

What is Yellowstone National Park named after?

Yellowstone River

Which volcanoes on Hawaii's Big Island are currently active?

Mauna Loa and Kīlauea

What river flows into Crater Lake?

None

How is volcanism at Lassen and Mount Rainier similar and different from Yellowstone?

Lassen/Rainier: subduction; Yellowstone: hotspot

How did the Diorite of North America form and what is the age of xenoliths?

Intrusive igneous; xenoliths are older

What coarse-grained igneous rock is mafic and rich in pyroxene?

Gabbro

How can you distinguish low- vs high-grade metamorphism?

Index minerals and foliation

What volcanic features are common at stratovolcanoes?

Lahars, domes, pyroclastic flows

When did Yellowstone Caldera form?

~640,000 years ago

Which direction is the Pacific Plate moving relative to the Hawaii hotspot?

Northwest

What volcanic rocks are associated with The Pinnacles?

Rhyolitic tuff and breccia

What are Chaos Crags and when did they form?

Rhyodacite domes ~1,100-1,200 years ago

What rock type dominates Yosemite National Park?

Granite

If an intermediate igneous rock partially melts, what is the melt enriched in?

Silica

What processes cause metamorphism?

Heat, pressure, and fluids

What eruption occurs along a linear vent with little explosive activity?

Fissure eruption

What type of volcano is Mauna Loa?

Shield volcano

What is the relationship between Brokeoff Mountain and Mount Tehama?

Brokeoff is a remnant of Tehama

How did Nevada Falls form?

Glacial carving and river erosion

How do aphanitic igneous rocks form?

Rapid surface cooling

How does volcanism at Hawaii differ from Yellowstone?

Basaltic effusive vs rhyolitic explosive

Why are the Painted Dunes red, brown, and yellow?

Iron oxidation