Earth Science 3rd test

pyroclastic flows (nuee ardente)

Fast-moving, extremely hot clouds of gas, ash, and rock fragments that flow down volcano slopes; very deadly.

Lava bombs

Large blobs of molten lava ejected into the air that solidify before landing.

Lapilli

Small volcanic fragments (ash-sized to pebble-sized) ejected during eruptions.

Pillow basalts

Rounded, pillow-shaped lava forms created when lava erupts underwater.

Aa lava

Thick, slow-moving, rough, jagged lava with sharp fragments.

Pahoehoe lava

Smooth, ropey lava that flows easily; hotter and less viscous than aa.

Volcanic gases

Water vapor, CO₂, SO₂ and other gases released from magma.

Lahars

Volcanic mudflows made of ash and water that flow down valleys like wet concrete.

Composition of magma

Determined mainly by silica (SiO₂) content.

Felsic magma

High silica, light-colored, thick (high viscosity), cooler (~650–800°C), explosive.

Mafic magma

Low silica, dark-colored, runny (low viscosity), hotter (~1000–1200°C), less explosive.

Viscosity

Resistance to flow; high silica = high viscosity.

Geotherm

Temperature increase with depth inside Earth.

Solidus

Temperature at which rock begins to melt.

Liquidus

Temperature at which rock is completely molten.

Shield volcano

Broad, gentle slopes; built from fluid basaltic lava (e.g., Mauna Loa).

Stratovolcano (composite)

Steep-sided, layered lava and ash; explosive (e.g., Mount St. Helens).

Cinder cone

Small, steep volcano made of loose pyroclastic fragments.

Crater

Small bowl-shaped depression at the summit.

Caldera

Large collapse structure formed when a magma chamber empties and the volcano collapses inward.

Caldera formation

Massive eruption empties magma chamber → roof collapses → large depression forms.

Volcanic Hazards

Lava flows, ashfall, pyroclastic flows, lahars, toxic gases, climate effects.

VEI (Volcanic Explosivity Index)

Scale (0–8) measuring eruption size based on ash volume and plume height.

Effusive/Hawaiian

Gentle lava flows.

Strombolian

Moderate bursts of lava fragments.

Plinian

Extremely explosive, tall ash columns.

Mount St. Helens eruption

Lateral blast, ash across U.S.

Krakatoa eruption

Massive explosion, tsunamis.

Eruption of Mount Vesuvius

Destroyed Pompeii.

Subduction zones

Explosive stratovolcanoes (Ring of Fire).

Hot spots

Volcanoes above mantle plumes (e.g., Yellowstone Caldera).

Mid-ocean ridges/rifts

Basaltic eruptions; new crust forms.

Ring of Fire

Volcanically active zone around Pacific Ocean.

Hotspots

Magma plume within plate.

Large Igneous Provinces (LIPs)

Massive outpourings of basalt over large areas.

Supervolcano

Extremely large caldera-forming eruption (e.g., Yellowstone).

Earthquake

Sudden release of energy when rocks break along a fault.

Energy source

Stored elastic strain from plate movement.

Seismometer

Instrument that records ground motion.

Seismogram

Recording of seismic waves.

Focus (hypocenter)

Point underground where rupture starts.

Epicenter

Point on surface directly above focus.

Body waves

Travel through Earth’s interior.

P-waves (Primary)

Fastest; compressional; travel through solids & liquids.

S-waves (Secondary)

Slower; shear motion; travel only through solids.

Surface waves (Love & Rayleigh)

Travel along surface; slowest, largest amplitude, most destructive.

Order of arrival

P → S → Surface waves.

Early warning systems

Use fast-moving P-waves.

Travel-time curves

Difference in P & S arrival times gives distance.

Triangulation

Use 3+ seismometers to pinpoint epicenter.

Normal fault

Tension; hanging wall moves down.

Reverse (thrust) fault

Compression; hanging wall moves up.

Strike-slip fault

Horizontal motion; vertical fault plane.

Right-lateral (dextral)

Opposite block moves right.

Left-lateral (sinistral)

Opposite block moves left.

Richter scale

Measures wave amplitude; less accurate for large/distant EQs.

Moment magnitude (Mw)

Measures total energy released; each whole number = 10× amplitude, ~30× energy.

Convergent (subduction)

Largest megathrust earthquakes.

Transform (strike-slip)

Shearing motion (e.g., San Andreas Fault).

Rifts (normal faults)

Extension (e.g., East African Rift).

Continent collision

Compression (e.g., Himalayas).

Intraplate

Within plates (e.g., New Madrid earthquakes).

Magnitude

Energy released.

Intensity

Damage experienced at location.

Aftershocks

Smaller quakes after main event.

Foreshocks

Smaller quakes before main event.

Liquefaction

Water-saturated sediment behaves like liquid during shaking.

Tsunami formation

Sudden seafloor displacement (usually subduction megathrust).

Tsunami vs storm waves

Tsunamis have long wavelengths, multiple waves, may begin with water retreat.

Crust

Thin outer layer.

Mantle

Thick rocky layer beneath crust.

Core

Outer core (liquid), inner core (solid).

Reflection

Waves bounce off boundaries.

Refraction

Waves bend when changing speed (Snell’s Law).

P-wave shadow zone (103–143°)

Caused by refraction at core-mantle boundary.

S-wave shadow zone (103–180°)

Because S-waves cannot travel through liquid outer core.