PHS-1010 Melinda Huff: Ch. 6 Volcanos

Scripture Match for Chapter 6 (Volcanoes)

Psalm 104:32 - 'He who looks on the earth and it trembles, who touches the mountains and they smoke!'

Magma vs. Lava

Magma is molten rock located beneath Earth's surface; lava is molten rock that has erupted onto Earth's surface.

Viscosity

A fluid's resistance to flow. High viscosity magma is thick and sticky; low viscosity magma is fluid and runny.

Primary Factors Controlling Magma Viscosity

1) Silica Content (#1 factor: high silica = high viscosity), 2) Temperature (higher temp = lower viscosity), 3) Dissolved Gases (volatiles).

Viscosity Effect on Eruption Style

Low-viscosity basaltic magma allows gases to escape easily, causing gentle/effusive eruptions. High-viscosity felsic/andesitic magma traps expanding gases, causing violent/explosive eruptions.

Basaltic vs. Andesitic vs. Rhyolitic Magma

Basaltic: low silica (~50%), low viscosity, high temp, fluid. Andesitic: intermediate silica (~60%). Rhyolitic/Felsic: high silica (~70%), high viscosity, low temp, sticky.

Pahoehoe Lava

Basaltic lava flow characterized by a smooth, ropy, or billowy surface; forms from hotter, highly fluid lava.

Aa Lava

Basaltic lava flow characterized by a rough, jagged, clinkery surface of blocky rubble; forms from cooler, more viscous lava.

Pillow Lava

Basaltic lava erupted underwater, forming interconnected bulbous or pillow-shaped structures due to rapid surface chilling.

Volcanic Gases (Volatiles)

Dissolved gases in magma (70-80% water vapor, CO2, SO2, N2) that expand near the surface, providing the explosive force for eruptions.

Pyroclastic Material (Tephra)

Pulverized rock, lava droplets, and ash ejected violently into the air during an explosive eruption.

Pyroclastic Classification by Size

1) Ash (<2 mm)

2) Lapilli/Cinders (2 to 64 mm)

3) Volcanic Blocks (hardened solid rock >64 mm)

4) Volcanic Bombs (streamlined molten rock ejected and shaped in air >64 mm).

Anatomy of a Volcano

Magma Chamber (subterranean reservoir) -> Conduit/Pipe (vertical channel) -> Vent (surface outlet) -> Crater/Caldera (steep summit depression).

Crater vs. Caldera

A crater is a small summit depression (<1 km) formed by eruption outflow; a caldera is a large circular depression (>1 km) formed by the collapse of a volcano summit into an emptied magma chamber.

Shield Volcano

A broad, gently sloping volcano built from successive layers of fluid basaltic lava. Features non-explosive, effusive eruptions. Examples: Mauna Loa and Kilauea (Hawaii).

Cinder Cone Volcano (Scoria Cone)

A small, steep-sided volcano constructed primarily of loose pyroclastic fragments (cinders/lapilli). Short eruptive lifespan. Examples: Sunset Crater, Parícutin.

Composite Volcano (Stratovolcano)

A large, steep, symmetrical mountain composed of alternating layers of lava flows and pyroclastics. Highly explosive/viscous lava. Examples: Mt. St. Helens, Mt. Rainier, Mt. Vesuvius, Mt. Fuji.

Pacific Ring of Fire

The zone surrounding the Pacific Ocean basin containing most of Earth's composite volcanoes, formed along subduction boundaries.

Pyroclastic Flow (Nuée Ardente)

A incandescent, high-speed cloud of scorching gas, ash, and pumice that rushes down volcanic slopes at speeds exceeding 100 km/h.

Lahar

A destructive volcanic mudflow produced when volcanic ash and debris mix with water from rain or melting snow/ice.

Mt. St. Helens 1980 Eruption Sequence

1) Earthquake triggered massive landslide -> 2) Uncorked lateral blast to the north -> 3) Vertical explosive ash column -> 4) Pyroclastic flows and lahars.

Three Caldera Formation Types

1) Crater Lake type (collapse of composite volcano after massive eruption), 2) Hawaiian type (gradual collapse from lava drainage), 3) Yellowstone type (supervolcano eruption of felsic magma).

Fissure Eruptions & Flood Basalts

Eruptions occurring along long narrow cracks in the crust, emitting massive volumes of fluid basaltic lava that cover entire landscapes. Example: Columbia River Plateau.

Secondary Thermal Volcanic Features

1) Geysers (intermittent hot springs spraying water under pressure), 2) Hot Springs (heated groundwater pools), 3) Fumaroles (gas/steam vents), 4) Mud Volcanoes (bubbling mud pools).

Volcanic Eruption Monitoring Tools

Seismic activity monitoring, tiltmeters/GPS for ground deformation, gas emissions analysis (SO2/CO2), and thermal imaging.

Review Q: Difference between Focus and Epicenter

Focus is the underground origin of fault rupture; Epicenter is the surface point directly above the focus.

Review Q: First seismic wave to arrive and media it travels through

P-waves (Primary waves) arrive first and travel through solids, liquids, and gases.

Review Q: Evidence from seismic waves that Outer Core is liquid

S-waves cannot pass through liquids, creating an S-wave shadow zone beyond 104° from the epicenter.

Review Q: Minimum number of seismographs needed for triangulation

At least 3 seismograph stations are required to locate an epicenter.

Review Q: Mercalli vs. Moment Magnitude difference

Mercalli measures subjective observed damage (I-XII); Moment Magnitude calculates objective total energy released.

Review Q: Primary factor controlling magma viscosity

Silica content is the #1 factor: higher silica produces higher viscosity (thicker) magma.

Review Q: Volcano type associated with subduction zones

Composite volcanoes (Stratovolcanoes) formed by explosive silica-rich andesitic/felsic magma.

Review Q: Volcano type formed from fluid basaltic lava

Shield volcanoes formed by gentle flows of low-viscosity basaltic lava.

Review Q: Eruption type at divergent boundary fractures

Fissure eruptions producing extensive flood basalts.

Review Q: Trigger for Mt. St. Helens 1980 eruption

A magnitude 5.1 earthquake caused a giant landslide that uncorked the pressurized magma chamber in a lateral blast.