Volcanoes

Frequency and Quantity There are ~ 550 historically active volcanoes There are ~ 550 historically active volcanoes About 60 erupt annually About 60 erupt annually The majority are 1) at the edge of continents and 2) underwater The majority are 1) at the edge of continents and 2) underwater Dormant volcanic cone in Japan

Mid ocean ridges

Mid ocean ridge

Rift valley magma plate

Mid ocean ridges Are continuous underwater mountain ranges Are continuous underwater mountain ranges Are formed by rising magma Are formed by rising magma Cause sea floor spreading Cause sea floor spreading Form a rift valley between spreading plates Form a rift valley between spreading plates Pillow lava at mid ocean ridge

Land based volcanoes Mt St Helens one day before eruption

Mt St Helens 4 months after eruption

Another before…

…and 2 years later

Land based volcanoes Are more dangerous than underwater types Are more dangerous than underwater types Form island chains like the Aleutian islands off Alaska Form island chains like the Aleutian islands off Alaska

The Ring of Fire

The ring of fire

The Ring of Fire Where the earth’s crustal plates meet, one plate will often slide under another Where the earth’s crustal plates meet, one plate will often slide under another As one plate slides under another, it heats up, mixes with water and the rock melts to form magma As one plate slides under another, it heats up, mixes with water and the rock melts to form magma This less dense magma then rises to feed volcanoes This less dense magma then rises to feed volcanoes

A volcano at the edge of a continent Sinking plate Mid ocean ridge Melted rock forming magma ?

Rift valleys and volcanoes Valley forms here Outward spreading

Rift valleys Are formed by plates moving away from each other Are formed by plates moving away from each other A valley forms by crust sinking between the diverging plates A valley forms by crust sinking between the diverging plates East Africa has a large rift valley with volcano formation East Africa has a large rift valley with volcano formation

The African Rift Valley

Africa’s rift valley

Rift valley

Kenya’s Rift valley

Hot Spots

Hawaiian Islands – hot spot

Volcanoes National Park

Hot Spots A hot spot is a fixed source of abundant rising magma A hot spot is a fixed source of abundant rising magma As a plate moves over the hot spot, magma forms undersea volcanoes; some of which rise above the ocean surface forming island chains As a plate moves over the hot spot, magma forms undersea volcanoes; some of which rise above the ocean surface forming island chains

Loihi Seamount A new volcanic cone is forming near Hawaii A new volcanic cone is forming near Hawaii It’s top is 1000 m (3000 feet) below the water surface, and it will break the surface in the next 10,000 to 100,000 years. It’s top is 1000 m (3000 feet) below the water surface, and it will break the surface in the next 10,000 to 100,000 years. Big Island of Hawaii Loihi

Map Projections How do you project a 3D object on a 2D map? How do you project a 3D object on a 2D map?

Mercator Projection

Winkel Tripel Projection

Maps of the Earth Cartography is the science and art of graphically representing a defined geographical area by means of a map. Cartography is the science and art of graphically representing a defined geographical area by means of a map. First off, the earth is round and maps are flat First off, the earth is round and maps are flat Map projections are ways of flattening a round earth into a useful picture; the resulting picture is distorted Map projections are ways of flattening a round earth into a useful picture; the resulting picture is distorted There is always distortion and compromises in accurately making a map There is always distortion and compromises in accurately making a map