Download Hawaii`s 5 active volcanoes are all located on

3.2.3 - What does Hawaii tell us?
Background: Some volcanoes are located far from plate boundaries in regions known as hot spots. Hot spots are
formed where high-temperature mantle material rises toward the surface in plumes that melt crustal rock turning it to
magma. The magma melts through the crust to form
volcanoes. These can occur within oceanic crust (e.g.
Hawaii) or they can occur on continental crust (e.g.
Yellowstone). As shown in the map, there are an
estimated 150-200 hot spots throughout the world.
Hawaii is special though. The islands break the
surface of the Pacific Ocean 3½ miles above the
oceanic crust. You just learned that the plates of the
lithosphere, including the Pacific Plate, are moving.
Hawaii actually gives us an amazing amount of
information about the rate and direction at which they
move. This is because while there are 8 visible major Hawaiian Islands, there is an underwater trail of them, that
when combines with the Emperor Volcanic Island chain, stretches nearly up to Russia. The unmoving
Hawaii plume is responsible for the creation of the Hawaiian – Emperor seamount chain, an over 5,800 kilometers
(3,600 mi) long chain of volcanoes, five of which
are active, two of which are dormant, and more than 123
of which are extinct, many having since been ground
beneath the waves by erosion.
Hawaii’s 5 active volcanoes are all located on the two
most Southeastern islands, Hawaii and Maui:
1)
Haleakale – most recent eruption 1790.
2)
Haulalai – most recent eruption 1801.
3)
Mauna Loa – has erupted 15 times since 1900,
but only twice since 1950. 1975 eruption lasted 1 day,
1984 eruption lasted 3 weeks. Due for an eruption.
4)
Kilauea – considered one of the most active
volcanoes in the world. 62 eruptions since 1790.
Current eruption started in 1983 and has been erupting
continuously since then.
5)
Lo’ihi – summit of volcano is still 970 meters
below surface of the ocean to the south east of the big
island of Hawaii. Estimated to reach the surface of the
ocean in 10,000-30,000 years and become an island, but
these are merely rough estimates.
Looking at the location of the 5 active volcanoes, scientists
are able to tell where the Hawaiian hot spot and the mantle
plume that is bringing magma from the asthenosphere up
to the surface. This magma will melt crustal rock that it is
passing through, turning that rock into magma as well. And
the location of the rest of the Hawaiian – Emperor
seamount chain tells us how the Pacific Plate has moved
over the Hawaiian hot spot for the last 100 million years.
The figure to the left gives a good cross section of this
process.
Using radiometric dating (specifically PotassiumArgon dating with a half life of 1.25 billion years)
of the volcanic igneous basalt rock that makes up
this mountain chain, geologists have been able to
date many of the different volcanoes along the
chain. With this information, it is clear that the
first quarter of this Hawaiian – Emperor seamount
chain existed when dinosaurs still roamed the
Earth.
Review Questions
1. What type of rock is being ejected
during a volcanic eruption?
2. Which islands of this mountain chain
are the oldest?
3. Which islands of this mountain chain
are the newest?
4. What would cause there to be only 5
active volcanoes, while there are 120+
that are extinct?
5. Why would the Emperor Seamount
Mountains be much smaller than the
Hawaiian Seamount Mountains?
6. What does that bend halfway through
the chain indicate?
7. Which direction is the Pacific Plate currently moving based on all of this information?
8. In Potassium-Argon radiometric dating, which element is the parent and which is the daughter
element?
9. Let’s pretend Potassium-40 has a half-life of 1,000 years and not 1.2 billion (easier math). How
many grams of Potassim-40 will be left from a 20g sample after 2,000 years?
Ttotal =
T½ =
Mstart =
Mend =
# ½ lives =
10. How many half-lives will it take for 50g of Potassim-40 to decay to 12.5g if the half life is 1,000
years?
Ttotal =
T½ =
Mstart =
Mend =
# ½ lives =