Tectonic & Seismic Hazards

Volcanoes

The outer layer we live on. 0-60 km thick. Can be

either continental or oceanic.

Semi-molten rock (magma), 2900km thick

Liquid. Made up of iron and nickel

Solid. Hottest part (55000 c), made up of

iron and nickel

• A theory that explains the

global distribution of

earthquakes, active

volcanoes, mountains and

other geologic features

by the movement of large

fragments of the of the

Earth’s crust

• Evidence includes

continental drift &

seafloor spreading

• Earth’s crust is broken into plates

and convection currents in the

mantle cause the movement of

these plates (conveyor belts)

• The tectonic setting of a region

determines if there will be any

volcanoes present and, if so, what

type

Spatial

distribution of

volcanoes is

related to plate

boundaries and

hot spots

Approx. 1500

active volcanoes

Approx. 2/3

volcano activity

occurs along the

‘Ring of Fire’

Mid-ocean ridges Subduction zonesHot Spots

Volcanoes occur at:

• Plates moving away from one

another, basaltic magma rises

to create new crust

• Can also occur on continents –

East Africa rift zone

• Plates moving towards each other.

Denser plate forced under less

dense plate and melts to become

magma. Magma rises to form

volcano

• Typically explosive in nature

Note: all three processes can occur under water or on land

Individual plumes of

magma rise to the crust

Chain of volcanoes produced as the plate moves over the hot spot

Located in the upper mantle and asthenosphere

Fueled by a high concentration of radioactive materials (energy source)

As the plate moves:

Location of volcanic features migrate

Hot spot remains in same location

Hot Spot Volcanoes

• A chain of volcanoes extends

northwest from the big island of

Hawaii

• The age of the volcanoes

gradually increase in this

direction

• The youngest volcano is Loihi (active

submarine volcano)

• The oldest above water volcano is

Kauai (4-6 million years old)

• At the far end of the chain, submarine

volcanoes, now eroded into

seamounts, can be dated to 78 million

years old

Direction of

plate movement

Hawaii, ocean hot spot

Yellowstone National Park,

continental hot spot

Direction of

plate movement

SHIELD VOLCANO

Largest, but much wider than they are tall

Gently sloping slides and broad summits

Non-explosive eruptions of very low-viscosity, basaltic magmas

Lava erupts through openings, or vents, in the volcano and flows down the sides

Muana Loa, Hawaii

Last eruption 1984

Skjaldbreidur, Iceland

Last eruption 9000 years ago

Piton de la Fournaise,

Reunion Island (France)

Last eruption 2017

COMPOSITE VOLCANO

(STRATOVOLCANOES)

Interlayered lava and pyroclastic deposits (debris blown from a volcano during an explosion)

Cone-shaped with steep sides

Combination of lava flow and explosive activity

Responsible for most of the death and destruction in history

Mt. Pinatubo, Phillipines

Mt. Fuji, Japan

Canadian Examples: Mount Meager

& Mount Garibaldi - dormant

Review: https://www.youtube.com/watch?v=yDy28QtdYJY

Watch first 12 minutes: https://www.youtube.com/watch?v=KlbnLnHSRzE

What are secondary

hazards of volcanoes?

MIND MAP PROJECT ( / 20)

Criteria:

• Minimum five secondary hazards (main

themes)

• Each theme needs to include further

detail – could be key facts about the

hazard, examples of when the hazard has

occurred and/or images & diagrams

• Mind map should be organized so

branches go from more general (main

themes) to more specific (detail)

• Use different colours and/or line types to

help distinguish between your main

themes

• Main questing, “What are secondary

hazards of volcanoes?” written in the

centre

What are secondary

hazards of volcanoes?

/5

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