Hawaii (USA): Hotspot Chains
1. Zoom from the xxxxx to Hawaii
2. We have already looked at a spectacular volcano at a subduction zone, Mt.
Fuji, and the bizarre volcanic environment at the Galapagos Rift, but if you
want to talk about volcanoes, nothing on Earth compares to Hawaii.
a. The big island of Hawaii (explain, Hawaii is both the set of islands and
the big island, so sometimes people just say the Big Island to avoid
confusion) – not only biggest volcano on Earth; biggest mountain on
Earth.
b. The highest point on the Big Island, Mauna Kea, is 13,796 ft (4,205 m)
above sea level. But it rises continuously from the base of the sea
floor, which is about 33,500 ft (10.2 km) – over 6.3 miles!
i. For comparison, Mt. McKinley, the tallest land mountain when
measured from the surrounding land, is only 18,000 ft above
surrounding land.
ii. And the Big Island is about 100 km across!
1. Shaped like a shield on the ground – often referred to as
a “shield volcano”
c. And the Big Island is only one of many islands
i. There are eight main islands: Hawaiʻi, Maui, Oʻahu,
Kahoʻolawe, Lanaʻi, Molokaʻi, Kauaʻi and Niʻihau
ii. However, they are part of about 130 islands and smaller islets
and rocks that stick up above sea level, spanning 1500 miles.
iii. But there are also about 80 independent underwater
seamounts that extend in a chain – the Hawaiian-Emperor
seamount chain – for 5800 km (3600 miles) right into the
subduction zone in Kamchatka (Siberia).
1. Which means that there were even more seamounts, but
they have subducted.
iv. Altogether, the amount of volcanic rock on the Pacific seafloor
is incredible. Over the past 65 million years, over a million
cubic km of lava have erupted.
3. Would have made a single massive volcano, except that the Pacific Plate has
continued to move!
a. Explain the formation of the H-E seamount chain
b. Rocks are youngest (0!) at Big Island and Loihi, and 87XX Ma at the
oldest point where it goes into the trench.
c. Classic example of a Hotspot
i. For the first scientists who put together the ideas of plate
tectonics, Hotspots were a vital part.
ii. Geodynamic modeling showed how it could come from the
core-mantle-boundary [explain]
iii. Soon after, every volcano that didn’t occur on a plate boundary
became a hotspot (>400!)
iv. Backlash – all sorts of other reasons to get volcanoes in the
middle of a plate!
v. Soon, some people were saying that there were NO mantle
hotspot plumes!
vi. Recent tomography, however, shows that there are indeed
some plumes of hot rock that rise up to the surface from the
base of the mantle. Hawaii is the quintessential example.
Largest flow for the longest time.
vii. Unknown connection with the biggest Geological Wonders of
the mantle: Pacific and African Megapiles [explain]
viii. Fixed relative to the deep mantle – hotspot reference frame.
ix. Still many questions remain: bend in H-E chain; initially
thought to be a sudden change in Pacific plate direction
1. When Kula plate disappeared
2. But some now say that the hotspot itself was moving
before 47 Ma
4. So when you visit the Hawaiian islands, you see a set of islands at different
stages of development – actually like looking back in time – just like looking
at how any one island would change over 5 million years or more.
a. Maui – >1; Molokai – ~2; Oahu – ~3; Kauai - 5
b. So, in terms of tourism, you get a wide range of sceneries
i. Hawaii – big, young, active volcanoes, lots of lava
ii. As you go west, erosion becomes greater – steeper sea cliffs;
deeper valleys carved by rain; more soil, so more lush
vegetation; fewer signs of volcanism; some of the top tourist
destinations – beautiful beaches, great snorkeling and scuba
diving, incredible scenery.
iii. Beaches can even be different colors – green (olivine) or black
(pyroxene)
iv. But as you go farther west, islands smaller, features less
pronounced. No more signs of active volcanism. Eventually,
just small flat islands, then seamounts.
v. Why do the islands disappear as they get older?
1. Erosion
2. Seafloor subsidence with age [explain]
c. But to a geologist, the gem is the Big Island
i. The whole island is a composite of recent volcanoes [show
map]
ii. The most active are on the southeast side – Kilauea: has been
erupting continuously since 1980
iii. Lava is hot and low in silica, so very fluid; not dangerous, you
can stand next to it, or even ON it, as it flows.
1. Sizzles in the rain; glows at night
iv. Flows all the way to the sea, though often crusts over on the
top to make lava tubes.
1. Kazumura lava tube has been surveyed at 40.7 miles
long and 3,614 feet deep, making it the longest and
deepest lava tube in the world
v. Lava flows as pahoehoe or aa
vi. Can form lava lakes that fill up and bubble and churn; Kilauea
Iki – looks like Mordor!
vii. Volcanic Activity monitored by the HVO
1. Moritors EQs as well as volcanoes;
2. Decollement zone – islands sit on layer of sediments!
3. Can be mag 7 as the whole island slides
4. Pacific Tsunamis are also monitored here
a. Pacific Tsunami Warning Center
b. Hawaii often gets his hard by tsunamis from Ring
of Fire EQs
viii. Island is large enough and the wind is also blowing fairly
constantly from the NE (trade winds), that the Big Island has
an incredible diversity of microclimates
1. Temperature is always moderate (buffered by ocean),
but wide variety of climates
2. Talk about experience of driving around the Island;
pampas to rain forest to desert, etc.
3. The north side, near Hilo, has some beautiful lush areas.
Drive around the corner, and it is raining, and you walk
through a jungle and see the beautiful Akaka falls.
4. Drive around the next corner and the rain stops and it is
dry plains.
5. Drive to the south, and the Kau desert is so dry that
NASA Astronauts trained there, and in Kilauea Iki,
because it is so dry.
6. Drive to the top of Mauna Kea and it is so high up that
there is often snow, and so clear that it is a great place
for astronomical observations.
7. So, if you visit Hawaii, sure, visit the beaches on the
other islands, but then take a plane over to the Big
Island and experience the Earth’s biggest volcano.
5. Top 5:
a. Louisville hotspot chain
b. New England Seamounts/Great Meteor Track
c. Ninety East ridge
d. Chagos-Laccadive Ridge
e. Special Mention – Olympus Mons (Mars) – largest volcano in the solar
system – what happens when you have a hot spot but no plate
motions.
Hawaii should go before Iceland - it is the quintessential hotspot.