1. Why is there volcanic activity in the middle of plates?

2. Hot Spots Learning Objectives
To be able to describe and explain the features of hot spots
To describe a case study of hot spot volcanoes

3. Key Ideas
Not all volcanic activity can be related to present day active plate margins
The Pacific Ocean shows a number of sub-parallel chains of volcanic islands which run diagonally across the Pacific plate
These islands are all shield volcanoes built up of basaltic lavas

4. The basalt that makes up these islands contain significantly more potassium and sodium than the basalts which make up the ocean crust.
This suggests that while the mantle forms the source for both these rocks suites, there must be a different mechanism involved in their formation
The formation of these volcanic islands is related to the occurrence of long-lived, stationary hot spots within the mantle

6. How do they form?
Hot spots occur when radioactive decay in the core is concentrated. It heats the lower mantle above it.
These hot spots heat the lower mantle creating localised thermal currents where plumes of magma rise vertically.
Hot spots provide localised intensive heat sources called mantle plumes - which partly melt the overlying plate, creating a continuous magma source.
Magma is lighter than the solid lithosphere and rises up, erupting at the surface.
Where crust is thin above a hot spot, this provides further opportunity for magma to escape as volcanic eruption.
Lava builds up over time, eventually creating an island, above the present sea-level.

7. Sort the cards into the correct order
ACTIVITY 1
Sort the cards into the correct order
Hot spots provide localised intensive heat sources called mantle plumes - which partly melt the overlying plate, creating a continuous magma source.
These hot spots heat the lower mantle creating localised thermal currents where plumes of magma rise vertically.
Hot spots occur when radioactive decay in the core is concentrated. It heats the lower mantle above it.
Lava builds up over time, eventually creating an island, above the present sea-level.
Where crust is thin above a hot spot, this provides further opportunity for magma to escape as volcanic eruption.
Magma is lighter than the solid lithosphere and rises up, erupting at the surface.

8. The formation of hotspots

10. Examples of Hot Spots
HAWAIIAN ISLANDS (series of volcanic islands) - in middle of Pacific Plate
YELLOWSTONE NATIONAL PARK - USA - hotspot located in interior of a continental plate (North American Plate)

11. 1. HAWAIIAN ISLANDS What direction is the Pacific Plate moving?
Here the bigger Island of Hawaii is currently over the hot spot

12. Formation of the HAWAIIAN ISLANDS
The current hotspot is near the southern end of the island of Hawaii.
Pacific plate moves northwest at a rate of 5-10cm a year.
Lo’ihi Seamount (YOUNGEST) is forming on the sea floor just south of Hawaii
North of Hawaii there are extinct volcanoes, being battered by erosion
Bends in the island chains show changes in plate movement.

13. Formation of the HAWAIIAN ISLANDS
New shield volcanoes appear above the hotspot.
Lava is runny
Pahoehoe – ropy lava and AA – blocky lava
Hawaii is home to the world’s largest volcano – Mauna Loa
As the volcano moves away from the hotspot the lava becomes more alkaline spatter cones may appear.
More violent eruptions e.g. Pyroclastic flows
More cone like volcanoes
Eg OLDEST - Haleakala on the island of Maui

14. World’s largest volcano!
Mauna Loa - Hawaii
World’s largest volcano!

16. 2. YELLOWSTONE NATIONAL PARK
Yellowstone appears to be over a continental hot spot that has produced a chain of volcanoes as the North American Plate moves southwestward over the hot spot

17. YELLOWSTONE NATIONAL PARK

18. Key Terms
Hotspot
Magma plume
Basalt
Volcanic islands
Lithosphere