The Hawaiian Islands: An
Oceanic Island ChainThe Hawaiian Islands: An
Oceanic Island Chain
The Hawaiian islands
form a chain that is stretched to the northwest and southeast. Ages of rocks from
different Islands in the Hawaiian island chain show that the islands are progressively
older to the northwest: Oahu, 3.4 to 2.2 Myr (millions of years); Molokai, 1.8 to 1.3 Myr;
Maui, 1.3 to 0.8 Myr; and the Big Island (Hawaii), less than 0.7 and still growing. This
trend is explained by the concept of a tectonic
plate moving slowing over a hotspot.
A hot spot is a plume of
magma or molten rock that rises from within the Earth, reaches the surface forming
underwater volcanoes which may grow tall enough to rise above the sea to form islands. In
the middle of the Pacific ocean, the Hawaiian hotspot remains stationary while the Pacific
plate slowly moves overhead to the northwest as illustrated in the cartoon on the left.
The area directly over the hot spot is volcanically active. The activity decreases and
eventually stops as the plate moves on. The result is the Hawaiian island chain.
The island of Hawaii is
commonly referred to as the Big Island. The Big Island is over the hotspot right now,
making it the youngest of the Hawaiian Islands. There are two active volcanoes on the Big
Island: Mauna Loa and Kilauea. Currently lava is erupting along the
East Rift Zone of Kilauea from the vent named Pu’u O’O. The Puna Ridge which we
are surveying is the underwater continuation of Kilauea’s East Rift Zone.
The illustration shows topography data for the Big Island and surrounding seafloor.
Yellows, greens, and blues are underwater and represent progressively deeper
seafloor. Reds and whites are the high points on the island.
The
next Hawaiian island that will come into being - already named Loihi - is building on the seafloor
southeast of Kilauea. It’s top is 1000 m (3000 feet) below the water surface, and it
will break the surface in the next 10,000 to 100,000 years.
The illustration to the left shows the southeast flank of the Big Island and offshore.
The shoreline is the boundary between yellow and green and is labeled.
Purples are the deepest water. Light reds are the highest peaks on the island.
The map of Loihi shown below was obtained from the Hawaiian Underwater Research Laboratory, and was made from multibeam bathymetry data. Color represents water depth with the reds being shallow and the blues being deep.
Maui is located about 140 km northwest of the Big Island. The Pacific plate is moving to the northwest at a speed of 0.00011 km/yr. How long ago was Maui over the hot spot? Remember that time equals distance divided by speed.
Check your answer below to see if you are correct.