Geology and Hollywood Exam 2

Where Do Volcanoes Form?

Volcanoes primarily form:

Along tectonic plate boundaries, especially subduction zones (e.g., the Ring of Fire).

At divergent boundaries, such as mid-ocean ridges (e.g., Mid-Atlantic Ridge).

Over hotspots, where mantle plumes bring magma to the surface (e.g., Hawaii, Yellowstone).

Why Do They Form Here?

Subduction zones: One plate sinks beneath another, melting due to water release from the subducted slab.

Divergent boundaries: Plates pull apart, reducing pressure and allowing magma to rise.

Hotspots: Plumes of hot mantle material melt through the crust.

What Is the Name of the Area with the Most Volcanic Eruptions?

The Ring of Fire, a horseshoe-shaped zone around the Pacific Ocean, has the highest concentration of active volcanoes.

What Is the Solidus?

The temperature at which a rock starts to partially melt.

What Is the Liquidus?

The temperature at which a rock is completely molten.

What Are the Three Ways to Melt a Rock?

Decompression melting – occurs when pressure is reduced (divergent boundaries, hotspots).

Flux melting – occurs when water or other volatiles lower the melting point (subduction zones).

Heat transfer melting – occurs when heat from rising magma melts surrounding rock (continental hotspots).

Where Do We Find Examples of Each?

Decompression melting: Mid-ocean ridges, Iceland.

Flux melting: Andes, Japan.

Heat transfer melting: Yellowstone, Hawaii (some aspects).

What Are the Three Types of Melt?

Basaltic (low silica, low viscosity).

Andesitic (intermediate silica, medium viscosity).

Rhyolitic (high silica, high viscosity).

How Does Silica Change Between the Three?

Higher silica = higher viscosity, making the melt more resistant to flow.

Why Does Silica Change Viscosity?

Silica forms strong molecular chains, making magma thicker and slower-moving.

Why Does Viscosity Matter to Volcanic Eruptions?

Low viscosity (basaltic magma) → Effusive, lava flows (shield volcanoes).

High viscosity (rhyolitic magma) → Explosive, gas buildup (stratovolcanoes, supervolcanoes).

Volcano Types

Shield Volcanoes: Broad, gently sloping, effusive eruptions (e.g., Mauna Loa, Hawaii).

Stratovolcanoes (Composite Volcanoes): Steep, layered, explosive (e.g., Mount St. Helens).

Cinder Cones: Small, steep, made of pyroclastic material (e.g., Parícutin, Mexico).

Supervolcanoes: Massive eruptions, global impact (e.g., Yellowstone).

Craters vs. Calderas

Craters: Small depression at the summit of a volcano.

Calderas: Large collapse features formed when magma chambers empty and the land above sinks.

What Is a Supervolcano? What Is the Local Supervolcano in the US?

A supervolcano is a volcano capable of producing eruptions with a Volcanic Explosivity Index (VEI) of 8.

Yellowstone is the most well-known US supervolcano.

Volcanic Hazards

Lava Flows – slow-moving but destructive.

Pyroclastic Flows – fast, hot, deadly gas and ash clouds.

Lahars – volcanic mudflows triggered by melting ice or heavy rain.

Ash Fall – can collapse buildings, disrupt air travel, and harm lungs.

Gas Emissions – CO₂, SO₂ can cause climate effects and health hazards.

Tsunamis – triggered by undersea eruptions or volcanic collapse.

Forecasting Volcanic Eruptions

Seismic activity – small earthquakes as magma moves.

Ground deformation – swelling of the volcano.

Gas emissions – changes in SO₂ and CO₂ output.

Temperature changes – rising heat near vents.

Preparing for Volcanoes

Evacuation plans.

Monitoring volcanic activity (USGS, seismometers, gas sensors).

Building barriers/diverting lava flows (in some cases).

Emergency supplies (masks for ash, water, food, etc.).

Magma forms when rocks in the Earth's mantle or crust partially melt due to changes in temperature, pressure, or the presence of volatiles. There are three main ways rocks can melt:

1. Decompression Melting

How it works:

When pressure decreases on hot mantle rock, it lowers the melting point, allowing it to melt.

Happens where plates pull apart or where a mantle plume rises.

Where it occurs:

Mid-ocean ridges (e.g., Mid-Atlantic Ridge).

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

Hotspots (e.g., Hawaii).

2. Flux Melting

How it works:

When water or other volatiles (like CO₂) are added, they lower the melting point of the surrounding rock, causing it to melt at a lower temperature.

Common in subduction zones, where water-rich oceanic plates sink and release fluids into the mantle.

Where it occurs:

Subduction zones (e.g., Andes, Japan, Cascades).

3. Heat Transfer Melting

How it works:

Hot magma from deeper in the Earth transfers heat to surrounding rocks, causing them to melt.

This occurs when magma intrudes into the crust, raising the temperature of existing rocks.

Where it occurs:

Hotspots under thick continental crust (e.g., Yellowstone).

Volcanic arcs where magma chambers heat the crust (e.g., Mount St. Helens).

Why Do Some Rocks Melt While Others Stay Solid?

Temperature – Rocks have different melting points based on their mineral composition.

Pressure – High pressure keeps rocks solid, while lowering pressure allows melting.

Water & Volatiles – These reduce the melting temperature of rocks.

Would you like a diagram or further clarification on any of these processes? 🔥🌋

You said:

types and characteristic of volcanos

ChatGPT said:

Types of Volcanoes & Their Characteristics 🌋

Volcanoes are classified based on their shape, eruption style, and magma composition. The main types are:

1. Shield Volcanoes

🔹 Shape: Broad, gently sloping, dome-like

🔹 Eruption Type: Effusive (lava flows, not explosive)

🔹 Magma Type: Basaltic (low silica, low viscosity)

🔹 Example: Mauna Loa (Hawaii), Galápagos Islands

🔹 Hazards: Lava flows, minor gas emissions

Why this shape?

Low-viscosity magma spreads widely before cooling.

2. Stratovolcanoes (Composite Volcanoes)

🔹 Shape: Tall, steep-sided, layered

🔹 Eruption Type: Explosive & periodic lava flows

🔹 Magma Type: Andesitic to rhyolitic (medium to high silica, medium to high viscosity)

🔹 Example: Mount St. Helens (USA), Mount Fuji (Japan), Mount Vesuvius (Italy)

🔹 Hazards: Pyroclastic flows, lahars, ash clouds, lava flows

Why this shape?

Alternating explosive eruptions (ash/pyroclastics) and lava flows build up layers.

3. Cinder Cone Volcanoes

🔹 Shape: Small, steep-sided, cone-shaped

🔹 Eruption Type: Short-lived, explosive, mostly pyroclastic

🔹 Magma Type: Basaltic to andesitic (low to medium silica, low to medium viscosity)

🔹 Example: Parícutin (Mexico), Sunset Crater (USA)

🔹 Hazards: Ash fallout, small lava flows

Why this shape?

Built from ejected volcanic fragments (cinders, ash, and lava bombs).

4. Lava Domes

🔹 Shape: Dome-like, steep-sided

🔹 Eruption Type: Slow lava extrusion, explosive potential

🔹 Magma Type: Rhyolitic (high silica, high viscosity)

🔹 Example: Mount St. Helens’ lava dome (USA), Mount Pelee (Martinique)

🔹 Hazards: Dome collapse → pyroclastic flows

Why this shape?

Sticky, high-viscosity lava piles up instead of flowing far.

5. Calderas (Supervolcanoes)

🔹 Shape: Large depression (collapsed volcano)

🔹 Eruption Type: Catastrophic super-eruptions

🔹 Magma Type: Rhyolitic (extremely high silica, extremely high viscosity)

🔹 Example: Yellowstone (USA), Toba (Indonesia), Crater Lake (USA)

🔹 Hazards: Global ash fallout, climate effects, pyroclastic flows

Why this shape?

When a massive magma chamber empties, the ground collapses.

Volcano Type vs. Magma Composition & Eruption Style

Volcano Type Silica Content Viscosity Eruption Type

Shield Low Low Effusive

Stratovolcano Medium Medium Explosive + lava flows

Cinder Cone Low-Medium Low-Medium Small explosive

Lava Dome High High Slow lava extrusion

Caldera Very High Very High Super-explosive