Physical Science 3/11-3/12

Volcanoes

New homework

• Read pages 714-717

• Try problems 2,3 and 7 on pg 717

Volcanoes

• Definition– An opening on the earth’s surface through

which molten rock flows and the material that builds up around

• Location

Are all volcanoes equally dangerous?

Types of Volcanoes

• Shield Volcanoes

• Composite Volcanoes

• Cinder Volcanoes

Hazards of volcanoes

Ash Fall

Pyroclastic Flows (Nuee Ardentes)

Mud Flows (Lahars)

Pyroclastic flow

Lahars

Note the mud on trees

Hazards

• Volcanic Bombs

Any sizeable fragment of rock thrown from an active volcano

gravel size up to boulders the size of buses

Volcanic Bombs

Hazards from the volcanic gases

The expansion of gases as it is heated

Produces most of the eruptive force of a ash volcano

Water Vapor is the most common gas released

Carbon Dioxide and Sulfur Dioxide are next

Gas hazards related to volcanoes

• Lake Nyos,• Cameroon, Africa• 1986• Release of Carbon

dioxide• Since CO2 is heavier

than air it hugs the ground

• This cloud was 100 m high

Constant release of gases

• Trees died by CO2 suffocation

Tsunami

Volcanic Hazards

• TsunamisMeans “Great Wave”

Not related to tides

Generated mainly by underwater earthquakes or landslides that displace a lot of wateror volcanic eruption in or under the water

Tsunamis

• Generally more than one wave

• Wave is much wider than typical ocean wave (wall of water)

• Travels around 500 mph in open water, slows down as it nears shore

• Height increases as waves nears shore– Some waves from Krakatoa reached over 100 ft tall

Final Hazard

• The unpredictability of some volcanoes lead some people to ignore warnings

Long-term volcanic benefits

• Fertile soil

• Volcanic products– Pumice– Sulfur– Diamonds– Metamorphic ore

Parts of a volcano• Vent – opening where molten rock is pushed out to the surface of

earth

• Magma Chamber - Chamber below volcano, holds the molten rock used in eruption

• Cone – mound created from solid material released from previous eruption

• Crater – hole (depression) at the top of volcano created by volcanic explosion

• Caldera – depression left on top of the volcano created by the collapse of the magma chamber

What are the differences and similarities between:

• Fumaroles

• Geysers

• Hot Springs

• Mud-pots

Fumaroles

Fumarole

An opening in the earth that emit gases

May be found some distance from the from the main vent

Gases are heated by the volcanic sources, travel through cracks and fractures to surface

Hot Springs

Hot Springs

• Openings that are filled with water that is heated by nearby volcanic activity

• The water may range from mild to scalding, and include both helpful and toxic minerals

Geyser

Geysers

A hot spring with specific ideal physical arrangement that allows it to periodically erupt

No convection, cold water cap over volcanically heated water

Mud Pots

Mud Pots

• Similar to a hot spring

• Form in places where water is scarce

• Mixture of a little water and volcanic ash

Where are volcanoes found in the world?

Convergent

Divergent

Other

One other place of volcano formation

• Hot Spots

• Created because a narrow stream of hot mantle raises up from the core-mantle boundary

• Long lasting point of heat, stationary with respect to the plates

• If formed under ocean crust, creates an island arc

Places where there might be a hot spot

• Hawaii

• Yellowstone

• Iceland

• Tahiti

• Up to 50 places in the world

Types of lava

Aa-

Pahoehoe-

Pillow lava-

Difference is based location and composition

Homework

• New Handout (Section 7.1-7.2)

• Section 7.1– All Questions except 4

Section 7.2

questions 1-6 and 10