Transcript Hawaiian Hot Spots

How come the
most volcanic
place on Earth
is nowhere
near a plate
margin?
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Photos of Active volcanoes in
Hawaii taken November 4th
2010
Hawaiian Hot Spots
The long trail of the Hawaiian hotspot
•
•
Hundreds of hot spots exist around the
world. These 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.
Main areas of hot spot activity
globally
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Hot spot volcanoes
In the animation above, why are the volcanoes to the left of the
‘hot spot’ extinct?
Hawaii
Size of the islands?
Many volcanoes but only 5 are
active.
Get smaller away
from main island
Why do we have volcanoes here
Volcano
Last
eruption
Loihi
1996 (A.D.)
Kilauea
Ongoing
since 1983
(A.D.)
1984 (A.D.)
12
1800 to 01
(A.D.)
1790
40
Mauna Loa
Hualalai
Haleakala
Distance
from Loihi
km
0
14
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 Loihi
Can you explain the reasons for the
formation of the Hawaiian islands?
The hot spot issue
The vast majority of earthquakes and volcanic eruptions
occur near plate boundaries.
The Hawaiian Islands, which are entirely of volcanic
origin, have formed in the middle of the Pacific
Ocean more than 3,200 km from the nearest plate
boundary.
In certain locations around the world, such as Hawaii,
volcanism has been active for very long periods of
time. This could only happen, if relatively small,
long-lasting, and exceptionally hot regions -- called
hotspots -- existed below the plates
This would provide localized sources of high heat
energy (thermal plumes) to sustain volcanism..
The shape of the Hawaiian Island-Emperor Seamounts
chain resulted from the Pacific Plate moving over a
deep, stationary hotspot in the mantle, located
beneath the present-day position of the Island of
Hawaii.
Heat from this hotspot produced a persistent source of
magma by partly melting the overriding Pacific
Plate.
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
• 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.
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Hawaiian Ridge
The length of the Hawaiian Ridge segment
alone, from the Big Island northwest to
Midway Island, is about equal to the
distance from Washington, D.C. to Denver,
Colorado (2,600 km). The amount of lava
erupted to form the Hawaiian-Emperor
chain is calculated to be at least 750,000
cubic kilometers-more than enough to
blanket the entire State of California with a
layer of lava roughly 1.5 km thick.
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Over time, countless eruptions cause the seamount to
grow until it finally emerges above sea level to form
an island volcano.
Continuing plate movement eventually carries the island
beyond the hotspot, cutting it off from the magma
source.
As one island volcano becomes extinct, another
develops over the hotspot, and the cycle is repeated.
This process of volcano growth and death, over many
millions of years, has left a long trail of volcanic
islands and seamounts across the Pacific Ocean
floor.
How a Hot Spot works
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The magma, which is lighter than the surrounding solid rock, then rises through
the mantle and crust to erupt onto the seafloor, forming a mound of solid magma
Over time, countless eruptions cause this to grow until it finally emerges above
sea level to form an island volcano.
Continuing plate movement eventually carries the island beyond the hotspot,
cutting it off from the magma source, and volcanism ceases. As one island volcano
becomes extinct, another develops over the hotspot, and the cycle is repeated.
This process of volcano growth and death, over many millions of years, has left a
long trail of volcanic islands and sea mounts across the Pacific Ocean floor.
The Hawaiian chain should get progressively older and become more eroded the
further they travel beyond the hotspot. The oldest volcanic rocks are on Kauai, the
north-western most inhabited Hawaiian island, are about 5.5 million years old and
are deeply eroded. By comparison, on the "Big Island" of Hawaii – south-eastern
most in the chain and presumably still positioned over the hotspot -- the oldest
exposed rocks are less than 0.7 million years old and new volcanic rock is
continually being formed.
TOPS Top 10 Geography in conjunction with www.sln.org.uk/geography
Task
In your own words, explain why there are
volcanoes in Hawaii.