16. Understand how plate tectonics and the "hot spot" theory can explain the origin of the Hawaiian Island chain and the different ages and positions of present-day islands and island remnants.
Information from Volcanoes in the Sea: The Geology of Hawaii, by Macdonald, Abbott and Peterson, 2nd edition, published by University of Hawaii Press, 1990.
The next three Learning Objectives, 16,17 and 18 will examine the history and
forces that formed the Hawaiian Island chain. These features impact plant
dispersal to the islands and shape the environment in which they grow.
I. GENERAL UNDERSTANDING of EARTH STRUCTURE and ORIGIN of VOLCANOES.
A. Earth's internal structure. (See Figure 16-A)
1. Crust is a thin solid outer layer of rock on
earth's surface. It is thicker under continents (30-70 km.) and thinner
under oceans (5 km.).
2. The mantle is below the crust. Its total composition is
not known but it is partly composed of the mineral peridotite. The earth's
interior is more dense than the crust so the crust "floats" on
3. The core is partly liquid and it is made up of molten iron-nickel.
B. Nature of earth's crust and Plate Tectonics.
1. The crust is made up of many "plates" - each about
50 miles thick. Since they are less dense, they float on the earth's mantle.
They are in constant motion relative to each other due to convection currents
under the crust in a process called Plate Tectonics.
2. Plate Tectonics is believed to be responsible for such geologic
phenomena as mountain-building, volcanoes, and earthquakes.
C. Movement of the Plates
1. Continents at one time formed one super continent called
Pangaea. Slowly Pangaea spread apart and the pieces that drifted
away are now recognizable as the world's major continents.
One indication for the original fit is demonstrated by the remarkable
matching symmetry between the Atlantic coasts of South America and Africa.
2. The slow movement of continents is explained by convection currents
inside the earth's mantle.
3. According to the plate tectonic theory, the ocean plates ride up under
continental plates. This gives rise to volcanic and earthquake
activity at the edges, particularly where the oceanic Pacific plate meets
continental plates. The "ring of fire" reference is due
to all the volcanic activity at the edges of the Pacific plate. (See Figure
For additional information on plate tectonics, visit the Cascade Volcanoes Observatory site.
II. ORIGIN of The HAWAIIAN ISLANDS.
A. Explanation of the Hawaiian Island Chain by a "Hot
1. Since the Hawaiian Islands are formed by volcanic activity
but are in the center of the Pacific Plate and not at the edges, a different
explanation is required for the volcanic activity which created the
islands. (See Figure 16-B)
2. T. Wilson in 1963 gave the following explanation which is broadly
accepted today. He suggested that the Hawaiian Islands were formed as Pacific
plates moved slowly northwest over some melting point, currently
described as a convection "plume." These plumes arise deep
within the mantle and, like torches, super-heat the section of crust with
which they intersect. The high-temperature plume create the "hot spot", the melting of the crust, as it is popularly called today.
3. The "hot spot" is hypothesized to be a melted area of the
earth's crust on the ocean floor which is in the middle of the Pacific plate.
The hot spot forming the Hawaiian Island chain is presently under part of
the Big Island.
4. Magma from the earth's interior (called lava when released) comes out
of the "hot spot", building a mound of cooled lava on the ocean
floor. After many thousands of years, it breaks surface and becomes an island.
For further information on Hot Spots, click here.
For another view of Hawaiian volcanoes, visit this site.
Lo'ihi is the ocean floor structure
to the south-east of the Big Island which eventually will become high enough
to rise above the surface of the ocean. This demonstrates that the process of island building in the Hawaiian Island chain is ongoing! (See Figure
How do scientists visit Lo'ihi? Click here to find out.
Lo'ihi is one of the only volcanoes in the world with its own Web page.
How will Lo'ihi be monitored in the future? Click here to find out.
For photos of Hawaii's volcanoes and another diagram of hot spots , click here.
How much do you really know about the Hawaiian Islands? Take this quiz to find out.
B. The actual extent of the Hawaiian Island Chain.
1. What we commonly call the Hawaiian Islands, from Kaua'i to
the Big Island of Hawai'i, are really part of a longer island chain called
the Northwestern or Leeward Island chain which is about 1,600 miles long.
This island chain includes small islands, atolls and pinnacles north of
Kaua'i, from Kure Atoll in the far north to Nihoa in the south. (See Figure
2. The islands from Kaua'i to the Big Island (Hawai'i) are actually under-ocean
mountain summits rising from the ocean floor.
The high mountain tops of Maui (Haleakala), and Hawai'i (Mauna Loa and Mauna
Kea) are actually the tallest mountain structures in the world! When measured
from the ocean floor they are about 5 1/2 miles high!
For a sea-floor view of the islands, click here.
C. The Interaction of the Hot Spot and movement of the Pacific plate.
This interaction results in island chains with linear age relationships:
that is, the youngest at one end of the chain and the oldest at the other.
(See Figures 16-E)
1. While the hot spot is releasing lava on the ocean
floor, the Pacific plate is moving slowly to the north-west. It carries
the forming island along with it and eventually away from the source of
lava. (Figure 16-C)
Eventually the island no longer increases in size, becomes dormant
(unlikely to erupt) and then extinct (no longer able to erupt). In terms of volcanic activity Kaua'i is extinct and O'ahu dormant .
2. If you trace the path of the Hawaiian Island chain, the oldest,
Kure is at the north-west tip, and the youngest, the Big
Island, is at the south-east tip of the chain.
This also correlates with the age of the islands: Kure about 30 million
years old, Kaua'i 5-6 million years old, and the Big Island 1 to half a
million years old. (See Figure 16-D)
D. Some other features of the hot spot and Plate Tectonics
1. The present rate of movement of the Pacific Plate, in relation
to the Hot Spot, is about 8 centimeters a year. The direction of
the plate movement is clearly from the north-west to the south-east
orientation of the island chain.
2. It is possible to speculate that the Emperor Seamount chain is an
even more ancient part of the chain and was formed when the Pacific
plate was going in a more northerly direction. Later, the Pacific plate
rotated and changed direction, causing the later island chain to be in the
north-west direction. (See Figure 16-f.)
3. Even on each island, there is an age gradient: The North Shore
of O'ahu is the oldest part and Makapu'u is the youngest part of O'ahu.
(See Figure 16-G)
4. The hot spot has two openings at the surface, giving islands a
"double-barreled" aspect, such as Mauna Loa and Mauna Kea on the
Big Island, each coming from one of these openings. On O'ahu, the Wai'anae
and Ko'olau Mountains are products of the two different openings of the
"hot spot". (See Figure 16-C)
5. It is still not understood how there were eruptions on the island
of O'ahu a million years ago after the last eruption, 200 miles away
from the hot spot. These eruptions created Diamond Head and Koko Crater,
among others. Scientists say that the island could still possibly erupt.
E. Implications of Island Formation on the developing Flora of the
1. For 38 million years, or even longer, large islands could
have been present at the current position of the island of Hawaii, the Big
2. As these islands moved north-west on the Pacific Plate and gradually
became eroded, their plants and animals could have had time to move "down"
the island chain to newer islands that were forming.
3. The ideas expressed above are logical but speculative. Because the older
islands above Kaua'i are extremely reduced in size and, because lava is
a poor preservative of fossils, strong data to support this explanation
is not easy to come by.
On the other hand, there is clear evidence today that native Hawaiian plants
and animals are (and were) able to disperse between the lower-island chain
in several ways.
One resulting pattern has older plant species (called relict species) more
common on Kaua'i, and younger species more frequent on the Big Island. Also,
the substantial number of Hawaiian native plants endemic to Kaua'i only
indicates its antiquity and isolation as compared to the other islands -
a direct result of its position on the hot spot formation "train."
Click here to leave your comments and suggestions.
[Learning Objectives Numerical Index]