How come the most volcanic

place on Earth is nowhere near a plate margin?

HotspotsLO: To be able to explain how

volcanoes are formed at hotspots

Main areas of hot spot activity globally

TOPS Top 10 Geography in conjunction

with www.sln.org.uk/geography

Hawaiian Hot Spots

Hotspots are areas in the lithosphere that are underlain by unusually hot magma. This heat causes partial melting of the lithosphere, eventually leading to volcanic activity. The Hawaiian Islands are a classic example of a volcanic grouping formed over one hot spot.

• Over thousands of years, as the Pacific Plate inched its way in a northwest direction, the stationary hot spot underneath the plate successively created volcanoes above it. Several of these volcanoes reached the ocean’s surface, forming the Hawaiian Islands.

http://www.youtube.com/watch?v=bYv6V5EJAKc

Photos of Active volcanoes in Hawaii taken November 4th 2010

Hot spot volcanoes

In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct?

Hawaii

Many volcanoes but only 5 are active.

The summit of Mount Everest is higher above sea level than the summit of any other mountain, but Mauna Kea is the tallest when measured from base to summit.

Why do we have volcanoes here

Volcano Last eruption

Distance from Loihi km

Loihi 1996 (A.D.) 0

Kilauea Ongoing since 1983 (A.D.)

12

Mauna Loa 1984 (A.D.) 14

Hualalai 1800 to 01 (A.D.)

40

Haleakala 1790 182

Why is Hawaii a chain of Islands?

As the plate continued to move, volcanoes, embedded in the plate, travelled away from the source of magma and eventually became extinct. This hot spot still continues to create new volcanoes. Thus, the islands are progressively younger from the northwest to the southeast. Several volcanoes in the chain are still quite active, and new underwater volcanoes are forming to the southeast of Hawaii as the Pacific Plate continues to move over the hot spot.

Height of the islands?

Taller islands are the youngest ones.

Older islands have reduced in size due to weathering and erosion

Lets look at the evidence

• Hawaiian Islands are in the centre of the Pacific plate

• Islands are smaller as we move away from Loihi

• Volcanoes decrease in activity away from Loihi

• Islands increase in age away from LoihiCan you explain the reasons for the formation of the Hawaiian islands?

• The Hawaiian volcanoes were produced by the Hawaiian hot spot, a localized source of high heat in the mantle which is presently under

the Big Island of Hawaii.

Heat from this hotspot produced a persistent source of magma by partly melting the overriding Pacific Plate.

The magma, which is lighter than the surrounding solid rock, then rises through the mantle and crust to erupt onto the seafloor, forming an active seamount.

Summary notes• Not on plate boundaries. • Unusually hot magma plumes in the mantle erupt through the crust. • This creates seamounts which are volcanic mountains beneath the sea.

Seamounts can rise above the ocean surface to create islands.• The Hawaiian Island chain formed as the Pacific crustal plate moved over a

stationary source of magma or hotspot.• There are many volcanoes on the Hawaiian islands, however, only a few are

active. When volcanoes move off the hotspot they lose their source of magma and become extinct.

• Volcanoes at the hotspot include:• Loihi – a submarine volcano that is continuing to grow in size. • The Big Island of Hawaii is at the hotspot and has several active volcanoes e.g.

Mauna Loa and Kilauea.

Example of a hotspot exam question (4)

Mark scheme

Example of what another student wrote and how the examiner marked

them!