Volcanoes and Other Igneous Activity

Volcanoes and Other Igneous Activity

• A volcano is an opening in a planet's crust, which allows hot magma, ash, rock and gases to escape from below the surface.

Introduction to Volcanoes + Top Five Volcano Webcams

Volcanoes are found on top of magma chambers and have large central vents through which the

tephra and gases erupt. At the top of the

central vent is a crater.

Tephra, from the Greek meaning

ash, are rock fragments and particles

ejected by the volcanic eruption.

Tephra = Pyroclastic materials

Factors Affecting Eruptions

10.1 The Nature of Volcanic Eruptions

Factors that determine the violence of an eruption • Composition of the magma

• Temperature of the magma

• Dissolved gases in the magma

Viscosity• Viscosity is the measure of a material's

resistance to flow.

What is more viscous?

10.1 What is viscosity?

Viscosity: The state of being thick, sticky, and semifluid in consistency.

Increasing Viscosity:WaterOrange JuiceCanola OilMaple SyrupMotor OilJamsPeanut butterGreaseCementGlass

Viscosity of two liquids



Viscosity• Factors affecting viscosity

- Temperature (hotter magmas are less viscous)

- Composition (silica content)

1. High silica—high viscosity (e.g., rhyolitic lava stream stone)

2. Low silica—more fluid (e.g., basaltic lava)

Magma Composition

Magma Definitions:

Magma Composition (Raise the BAR)

Basaltic: (Touchstone) Fine-grained black volcanic rock.

Andesitic: (Andes Mountains) Fine-grained brownish-gray volcanic rock of intermediate composition between basaltic and rhyolitic.

Rhyolitic: (Lava-stream stone) Fine-grained pale volcanic rock of granite composition.

Volcanic Material

10.1The Nature of Volcanic Eruptions

Lava Flows• Basaltic lavas are more fluid because lower

silicates.

- Pahoehoe lava (resembles braids in ropes)

- Aa lava (rough, jagged blocks)

• Types of lava

Gases• One to 5 percent of magma by weight

• Mainly water vapor and carbon dioxide

• The magma that flows from volcanoes contains rock/minerals including silica.

• If the magma is high in silica, the higher the viscosity and the less the lava flows.

• The lower the silica level, the lower the viscosity and the more easily the lava flows.

Magma Flow Conclusions:

Pahoehoe (Ropy) Lava Flow

Pahoehoe lava flow video

Slow-Moving A’a Flow

A'a Lava flow

Which are they?



Dissolved gases • Mainly water vapor (H2O) and carbon dioxide

(CO2), but also include, sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF)

• Gases expand near the surface

• A vent is an opening in the surface of Earth through which molten rock and gases are released.

• Provide the force to extrude lava



Dissolved gases

Many different gases can be ejected from a volcano into the atmosphere. The gases provide the force to eject the tephra from the central vent.

Dissolved Gases

• The more viscous (thicker) the magma, the slower the gases can rise through the central vent and, therefore, the more pressure that builds and the more explosive the eruption.

Sooooo…….

Thicker lava (more viscous) = more pressure building up =

more explosive eruption

Dissolved Gases

Volcanic Material


Pyroclastic Materials• Pyroclastic materials is the name given to

particles produced in volcanic eruptions.

• The fragments ejected during eruptions range in size from very fine duct and volcanic ash (less than 2 millimeters) to pieces that weigh several tons.

• Sizes from 2 mm to 2 tons!

Tephra = Pyroclastic materials

Volcanic Material


Pyroclastic Materials (Lava Solids!) (pyro (fire) + clast (broken in pieces)

• Types of pyroclastic material- Ash and dust—fine, glassy fragments - Pumice—frothy, air-filled lava

- Lapilli—walnut-sized particles- Cinders—pea-sized particles

• Particles larger than lapilli

- Blocks—hardened lava- Bombs—ejected as hot lava

Volcanic Material


Pyroclastic Clouds (Flows)

• These fast moving clouds of hot gas and rock are the Real Killers!

- Normally hug the ground and flow downhill- Up to 700 km/hr (450 mph), cannot outrun them.

- People cooked in the 1000 °C (1,800 °F) heat.

- Body instantly reduced to charcoal.

Pyroclastic Clouds: The Real Killers

Types of Volcanoes


The four main volcanic types are: 1) shield volcanoes, 2) cinder cones, 3) composite cones, and 4) lava domes.

• A volcano is a mountain formed of lava and/or pyroclastic material.

• A conduit, or pipe, carries gas-rich magma to the surface.

Anatomy of a Volcano

• A crater is the depression at the summit of a volcano or that which is produced by a meteorite impact.

Anatomy of a “Typical” Volcano

Types of Volcanoes

There are three major types of volcanoes (and one minor):

•Shield volcanoes

•Cinder cones

•Composite/Stratovolcano

•Lava domes (minor)

Types of Volcanoes


Shield Volcanoes (made by lava liquid)

• Shield volcanoes are broad, gently sloping volcanoes built from fluid basaltic lavas.

• Liquid, fluid lava flows versus pyrocastic solid lava.

• Shield volcanoes have shallow-sloping sides (looking like a shield from the side or from the air).

• These volcanoes form from fluid lava that can travel for long, long distances before hardening. This leaves a large volcano with a small slope.

Shield Volcanoes

Hawaii Big Island: Shield flow volcano

Examples of Shield Volcanoes

• Kilauea

• Lo`ihi

• Mauna Loa

• Hualalai

• Mauna Kea

• Kohala

Types of Volcanoes


• Cinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent and then cool quickly in the air. These accumulate to make the sides of the volcano.

- Steep slope angle

- Rather small in height and size

- Frequently occur in groups

Cinder Cones (made by lava solids)

The cinders up-close!

Cinder Cones

Cinder Cone: Pericutin, MX

Paricutin, MX: Cinder Cone Volcano

Cinder Cone: Sunset Crater,AZ

Types of Volcanoes


Composite Cones (a.k.a. stratovolcanoes)• Composite cones are volcanoes composed of

both lava flows and pyroclastic material.

- Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier).

- Large size and high in height - Interbedded lavas and pyroclastics

- Most violent type of activity

Mount Vesubius/Pompeii: Composite Cone

• Stratovolcanoes are tall and steep. They have periodic, explosive eruptions.

• These volcanoes are tall and steep because they erupt viscous (thick) lava that cools and hardens before is spreads very far.

• Composite means BOTH…both what?

• Made by BOTH lava solids (pyroclastic materials) and by lava liquid (lava flows).

Composite Cones

Mammoth Mountain, CA (dormant)Mt. Fuji, JapanMt. Pinatubo, PhillipinesMt. Etna, SicilyMt. Shasta, CA (dormant)Mt. Unzen, JapanMt. Rainier, WAMt. St. Helens, WAKrakatoa, IndonesiaMt. Vesuvius, Italy

Mount St. Helens Before and After the May 18, 1980, Eruption

Before After

Krakatoa (1883) decreased global temperatures by 4⁰ F for 5 years

• Lava domes are a type of volcano that are formed by lava that is too viscous to flow any great distance.

• The thick lava extrudes from the central vent, cools down and hardens around the vent. Lava domes can occur by themselves or on the flanks of large composite volcanoes.

• Lava domes are often very, very dangerous. Thinking about the viscosity of the lava, why do you think they are dangerous?

Lava Dome

Profiles of Volcanic Landforms

Other Volcanic Landforms


Calderas

• Calderas are large depressions in volcanoes.

• Formed by collapse

• Nearly circular

• Size exceeds one kilometer in diameter



Volcanic Neck

• A volcanic neck is a cylindrical-shaped landform standing above the surface created by magma solidifying in the vent of a volcano. Erosion of the sides of the volcano exposes the neck.


A Volcanic Neck: Devil’s Tower, WY

Build Your Own Volcano!


Click here to: Build Your Own Volcano!



• Wide areas formed when fluid basaltic lava extrudes from crustal fractures called fissures.

Lava Plateaus

Complete Study Guide 10.1

• A supervolcano is a volcano that produces an eruption that ejects more than 1,000 km3 of tephra (240 mi3).

• This amount of ejecta is thousands of times larger than most historic volcanic eruptions.

• Supervolcanoes usually occur when magma in the Earth rises into the crust from a hotspot but is unable to break through the crust. Pressure builds in a large and growing magma pool until the crust is unable to contain the pressure….

…. and BAM!!!!!!!!!!!!!!!!!!!!!!!!!

The world is changed!

1) Yellowstone, WY

2) Long Valley, CA (Mammoth Mt.)

3) Valles Caldera, NM.

4) Lake Toba, Indonesia (Largest eruption in the past 25 million years! It erupted 74,000 years ago.)

5) Taupo Volcano, New Zealand;

6) Aira Caldera, Japan.

Hotspot Locations for Yellowstone Supervolcano (million of years ago)

• An eruption of a supervolcano can cause a global climatic change (typically a mini-Ice Age, “volcanic winter”) and major species extinctions!

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Volcanoes and Other Igneous Activity