Hawai‘i Volcanoes, Yellowstone, Virgin Islands & Arches National Park: Geology & Volcanism

Hot Spot

An upwelling of exceptionally warm and buoyant mantle from the deep Earth that creates volcanic activity.

Hot Spot Track

A trail of volcanic islands or seamounts formed as tectonic plates move over a stationary hot spot.

Shield Volcano

A broad, gently sloping volcano formed by the eruption of low-viscosity mafic lava.

Basalt

A mafic volcanic rock low in silica and rich in iron and magnesium, common in Hawai'i.

Effusive Eruption

A volcanic eruption characterized by lava flows rather than explosive activity.

Fire Fountain

A type of eruption where lava is ejected in a fountain-like manner due to gas expansion.

Fissure Eruption

An eruption that occurs along cracks in the Earth's surface, producing lava flows.

Scoria

Vesicular basalt formed during explosive eruptions.

Pele's Hair

Thin strands of volcanic glass formed by rapid cooling and stretching of lava droplets.

Pele's Tears

Teardrop-shaped volcanic glass formed as droplets cool mid-air.

Volcanic Bomb

Large blobs of lava that solidify before hitting the ground.

Pahoehoe Lava

Smooth, ropey lava formed from hotter, less viscous flows.

'A'ā Lava

Rough, clinkery lava formed from cooler, more viscous flows.

Lava Tube

A tunnel formed when the surface of a lava flow cools and hardens while the interior continues to flow.

Skylight

An opening in the roof of a lava tube where the crust has collapsed.

Lava Tube Cave

A hollow tunnel left behind after lava drains from a lava tube.

Mantle Xenolith

Chunks of the Earth's mantle brought to the surface by erupting magma, often containing olivine.

Eruption

A sustained period of volcanic activity involving magma, pyroclastics, and gases.

Episode/Phase

A distinct style or location of eruption within a larger event.

Pulse

A single explosion or lava burst within an episode.

Volcanic Hazards

Lava flows, volcanic gases, ashfall, earthquakes, and ground deformation.

Caldera

A large volcanic crater formed by the collapse of a magma chamber after an eruption.

Hot Spot Volcanism

Volcanism caused by a stationary mantle plume.

Supervolcano

A volcano capable of producing an eruption with ejecta greater than 1,000 km³.

Hydrothermal Features

Includes geysers, hot springs, mud pots, and fumaroles, driven by heat from the underlying magma chamber.

Geyser

A hydrothermal feature that intermittently erupts water and steam due to pressure buildup.

Travertine

A form of limestone deposited by mineral springs, especially hot springs.

Obsidian

Volcanic glass formed from rapid cooling of silica-rich lava.

Rhyolite

A silica-rich volcanic rock common in Yellowstone, associated with explosive eruptions.

Lava Flow

Molten rock that flows from a volcano.

Earthquake Swarms

Clusters of earthquakes that occur over a short period.

Carbonate Platform

A sedimentary structure formed in warm, shallow marine environments.

Reef Limestone

Limestone formed from coral reefs and marine organisms.

Tectonic Uplift

The rising of Earth's crust due to tectonic forces.

Marine Sedimentary Rocks

Rocks formed from sediments deposited in marine environments.

Coral Reef

A marine ecosystem built by coral organisms.

Fossil Coral

Preserved remains of ancient coral found in limestone formations.

Turbidites

Sedimentary deposits from underwater landslides or turbidity currents.

Volcaniclastic Rocks

Sedimentary rocks composed of volcanic fragments.

Island Arc

A curved chain of volcanic islands formed above a subduction zone.

Subduction Zone

A tectonic boundary where one plate sinks beneath another. Responsible for volcanic activity in the region's past.

Dune

A hill of sand built by wind. Indiana Dunes NP features large coastal dunes formed by Lake Michigan winds.

Parabolic Dune

U-shaped dunes with arms pointing upwind. Common in Indiana Dunes due to vegetation anchoring.

Beach Ridge

Elevated ridges formed by wave action along a shoreline. Found parallel to Lake Michigan.

Glacial Till

Unsorted sediment deposited by glaciers. Found beneath the dunes and throughout the region.

Outwash Plain

Flat area formed by meltwater from glaciers depositing sediments. Present in the park's geology.

Lake Michigan

The lake influences sediment transport and dune formation in the park.

Aeolian Processes

Wind-driven processes that shape dunes and transport sand.

Longshore Drift

Movement of sediment along the coast by wave action. Shapes the shoreline of Indiana Dunes.

Blowout

A depression formed by wind erosion in a dune. Common in areas with disturbed vegetation.

Sand Mining

Extraction of sand for industrial use. Historically impacted the dunes before conservation efforts.

Arch

A natural rock formation where erosion has created an opening. Arches NP has over 2,000 documented arches.

Erosion

The process of wearing away rocks by wind, water, and ice. Responsible for shaping arches and other features.

Salt Tectonics

Deformation caused by movement of underground salt layers. Influenced the formation of arches.

Entrada Sandstone

A Jurassic-age rock unit that forms many of the arches due to its composition and structure.

Dewey Bridge Member

A weaker layer beneath Entrada Sandstone that contributes to arch formation through differential erosion.

Jointing

Fractures in rock that guide erosion and arch development.

Fins

Narrow rock walls formed by erosion along joints. Arches often form in fins.

Desert Varnish

Dark coating on rock surfaces caused by oxidation and microbial activity. Common in Arches NP.

Weathering

Breakdown of rocks by chemical and physical processes. Key to arch formation.

Balanced Rock

A famous feature in Arches NP where a large rock rests atop a narrow pedestal due to differential erosion.

Plate Velocity

Calculated by measuring the age and distance between volcanic islands in the hot spot track using the formula: Velocity = Distance / Time.

Mafic Volcanic Rocks

Primarily basalt, which is low in silica (SiO₂ < 55%) and rich in iron and magnesium.

Pahoehoe

Smooth, ropey lava formed from hotter, less viscous flows.

'A'ā

Rough, clinkery lava formed from cooler, more viscous flows with higher strain.

Pyroclasts

Includes scoria, Pele's tears, Pele's hair, and volcanic bombs.

Volcanic Bombs

Large blobs of lava that solidify before hitting the ground.

Lava tubes

Hollow tunnels formed when the surface of a lava flow cools and hardens while the interior continues to flow.

Skylights

Openings in the roof of a lava tube where the crust has collapsed.

Lava tube caves

Caves that form when lava tubes fully drain and remain structurally intact.

Kīlauea

A volcano in Hawai'i that has been erupting frequently, with notable episodes in 2020, 2021-2023, and ongoing activity since December 2024.

Mauna Loa

A volcano in Hawai'i that last erupted in late 2022.

Active volcanoes in Hawai'i

Kīlauea, Mauna Loa, and Hualālai.

Dormant volcano in Hawai'i

Mauna Kea.

Extinct volcano in Hawai'i

Kohala.

Eruptive activity location since 1950

Most eruptions have occurred at Kīlauea, especially in the East Rift Zone and Halemaʻumaʻu Crater.

Mantle xenoliths

Chunks of the Earth's mantle brought to the surface by erupting magma, often containing olivine.

Geysers

Hot springs that periodically erupt with steam and water, formed when groundwater is heated by magma.

Hot springs

Groundwater heated by geothermal energy that rises to the surface without erupting.

Mudpots

Acidic hot springs with limited water supply that create a bubbling, muddy mixture.

Fumaroles

Openings in the Earth's crust that emit steam and volcanic gases.

Major caldera-forming eruptions in Yellowstone

Three major eruptions: Huckleberry Ridge eruption (~2.1 million years ago), Mesa Falls eruption (~1.3 million years ago), and Lava Creek eruption (~640,000 years ago).

Yellowstone hot spot track

A chain of volcanic centers formed as the North American Plate moved over a stationary mantle plume.

Types of volcanic rocks in Yellowstone

Rhyolitic and basaltic volcanic rocks, with obsidian also being common.

Volcanic hazards in Yellowstone

Explosive eruptions, ashfall, pyroclastic flows, lava flows, earthquakes, and hydrothermal explosions.

Virgin Islands formation

The Virgin Islands formed through tectonic activity involving the subduction of the Atlantic plate beneath the Caribbean plate.

Volcanic rocks in Virgin Islands

The islands contain volcanic rocks such as basalt and andesite.

Sedimentary rocks in Virgin Islands

The islands contain sedimentary rocks like limestone and sandstone.

Sedimentary structures in Virgin Islands

Sedimentary structures include bedding, cross-bedding, ripple marks, and graded bedding.

Sedimentary environments in Virgin Islands

Sedimentary environments include coastal beaches, lagoons, reefs, and shallow marine settings.

Fossils in Virgin Islands

Fossils in the Virgin Islands include marine organisms such as corals, mollusks, and foraminifera.

Types of coral reefs in Virgin Islands

The Virgin Islands host fringing reefs, barrier reefs, and patch reefs.

Carbonate rocks in Virgin Islands

Carbonate rocks include limestone and dolostone, formed from the accumulation of carbonate minerals in marine environments.

Glacial landscape shaping

Glaciers sculpted the landscape by eroding bedrock and depositing sediments.

Moraine

A moraine is a ridge or mound of glacial debris (till) deposited at the edges of a glacier.

Kettle lake

Kettle lakes form when blocks of ice left by retreating glaciers melt and create depressions that fill with water.

Dune formation

Dunes are mounds of sand formed by wind deposition.

Types of dunes in Indiana Dunes

Indiana Dunes features parabolic dunes, transverse dunes, and foredunes.

Sedimentary structures in dunes

Sedimentary structures include cross-bedding, ripple marks, and grain sorting.

Sedimentary rocks in Indiana Dunes

Sedimentary rocks include sandstone and conglomerate, formed from compacted and cemented sand and gravel.