Marine Science Chapters

2.4.2

Hawaii: Geology, Plate Tectonics/Hot Spot




Cross sectional view of Hawaii

An artist's diagram of a cross sectional view of Hawaii.

Hawaii is geologically a unique place on Earth because it is caused by a 'hot spot.' Most islands are found at tectonic plate boundaries either from spreading centers (like Iceland) or from subduction zones (like the Aleutian Islands). There are few 'hot spots' on Earth and the one under Hawaii is right in the middle of one of the largest crustal plates on Earth - the Pacific Plate. A geologic 'hot spot' is an area in the middle of a crustal plate where volcanism occurs. It is easy to geologically explain the volcanism at plate spreading centers and subduction zones but not as easy to explain a 'hot spot.' The molten magma breaks through the crustal plate (theories describe this as either from a weak/thin part of the plate or a particularly hot part of the molten magma). A hot spot under the American plate is why Yellowstone National Park has geysers and other thermal features. If the hot spot is under the seafloor (as it is in Hawaii) it produces undersea volcanoes. Some of these volcanoes build up to the surface of the ocean and become islands. Over millions of years the plate may move across the 'hot spot' and the original volcano become extinct but a new volcano will begin to form in the area of the 'hot spot.'


A bird's eye view of Hawaii

A bird's eye view of Hawaii from an artists's perspective.

The northwest moving Pacific Plate has moved across the 'hot spot' that created the Hawaiian Islands for millions of years. This movement has left the northwest trending island chain (of over 20 islands and atolls) we call Hawaii. As islands move northwest, away from the 'hot spot,' they begin to erode and become volcanically inactive. Over time the island may erode so much it is no longer an island but an underwater seamount. Kauai is the oldest of the main Hawaiian Islands now, having formed some 5 million years ago, with its volcano considered to be extinct and fully in the process of erosion. Oahu is next, its volcanism is considered to be inactive. Then Maui with its Haleakala crater that could still come to life one more time. And the youngest island is the 'Big Island' of Hawaii itself, with surface lavas all less than one million years old. It still has active volcanism. On the seafloor 20 miles to the southeast of Hawaii is an active volcanic area with periodic eruptions. This area is called Loihi and will be the site of the next Hawaiian Island if geologic processes continue as they have for millions of years but it may be over 10,000 years before this happens.


Pele, goddess of fire
Pele, goddess of fire, as portrayed in a mural at the Jagger Museum on the rim of Kilauea.
Map of Hawaii's 5 volcanoes Steam vents












Sulfur deposits
Map of the five volcanos that made the big island of Hawaii (left). Steam vents (Volcano House is in the background where tourists eat and stay) and sulfur deposits near the rim of Kilauea volcano (right).
Kilauea volcano with Halema'uma'u crater
Kilauea volcano is active on its flanks today. Inside the volcano is Halema'uma'u crater in the background.
Sulfur Banks near Kilauea Closeup of sulfur deposits
Sulfur Banks is an area near the visitor center at the rim of Kilauea volcano (left). Closeup of the sulfur deposits reveal beautiful crystals (right).
Hawaii has active volcanism today. The big island of Hawaii is the largest of the current Hawaiian Islands and is made of five volcanoes (Kohala, Mauna Kea, Hualalai, Mauna Loa and Kilauea). Kohala last erupted 60,000 years ago and Mauna Kea last erupted 3,500 years ago. These two volcanoes are considered dormant. Hualalai's last eruption was in 1801. Only two of Hawaii's volcanoes are active today - Mauna Loa and Kiluaea. Mauna Loa erupted in 1984 and Kilauea is considered to be one of the most active volcanoes on Earth today. It has erupted 30 times in the last 40 years. Hawaii is one of the few places on Earth where you can safely watch the volcanic processes that shape our Earth.


Diagram of Kilauea volcano
Cross sectional diagram of Kilauea volcano (from the Jagger Museum) showing the east rift zone (most active area today).
 2010 Halema'uma'u crater
Halema'uma'u, a pit crater, inside Kilauea Caldera started erupting in 2008 creating an almost constant plume of steam and volcanic gases (sulphur dioxide). This has caused Hawaii Volcano National Park to close part of its Crater Rim Drive (but there is still plenty to see inside the National Park). In fact, if you are at the National Park after dark then Halema'uma'u crater is usually glowing red - best viewing from the Jagger Museum (which is closed after dark so you need to bring a flashlight).
Halema'uma'u crater viewed from the Jagger Museum before 2008 activity Evening view of the east rift zone of Kilauea from the coast
View of Halema'uma'u crater (inside Kilauea Caldera) as viewed from the Jagger Museum prior to the 2008 eruption (left). An evening view of the east rift zone of Kilauea from the coast (right). Evenings give the best views of the red hot lava from a distance.
Kilauea volcano has active vents that erupt in various places on the southeastern side of Hawaii. The 'hot spot' volcanos are considered to be gentle volcanos and different than the violent volcanic eruption from Mount Saint Helens that killed many people in the State of Washington in 1980.


Pu'u O'o vent Pu'u O'o vent
Pu'u O'o vent August 2002.
Erupting craters inside Pu'u O'o vent
Erupting craters inside Pu'u O'o vent.
Lava flow through forest
Lava flow through forest on the East Rift Zone of Kilauea.
Burning trees due to new lava flow
Burning trees due to new lava flow on East Rift Zone of Kilauea August 2002.
Pu'u O'o vent is active now in the east rift zone of Kilauea. It is far from most roads but helicopters can safely take you there for an aerial view.


Helicopter view of lava flow Lava flowing into the ocean and a new black sand beach
Helicopter view of lava flowing toward the ocean (left). Lava flowing into the ocean and a new black sand beach from East Rift Zone, Kilauea Volcano, August 2002 (right).
Lava flow toward the ocean with steam Crack in recent lava flow
Lava flow toward the ocean with steam (left). Crack in recent lava flow shows cooled surface but still molten layers under it (right).
Warning sign near recent lava flows Trail to recent lava flows
Warning sign near recent lava flows reminds visitors that volcanism can be dangerous (left). Trail to recent lava flows is marked with yellow tags to help visitors see the lava flows and remain safe (right).
Lava flowing into the ocean is rarely seen but, in Hawaii, it is possible for the general tourist to view this. Hawaii's lava is slow moving and somewhat predictable in its path. The Hawaii Volcanoes National Park sets up a marked trail and signs to guide tourists for the best views of the eruptions of Kiluaea while keeping them reasonably safe. Every day the situation with the location and activity level of the lava changes and park personnel are kept busy during active periods.


Lava flows 2004

Flowing lava Closeup flowing lava
Lava Flows
Lava flows from Pu'u O'o during the summer of 2004 (above) provided great viewing for anyone who was willing to walk about a mile along the marked path. The flows were active but at the speed of a slowly moving snail so viewing them was easy. Flowing lava may be over 2,000 degrees Fahrenheit with the air next to it close to 600 degrees. It is easy not to get too close to the flowing lava as you break out into a sweat when you are a few feet away. Usually the Trade Winds are blowing near the flowing lava which allows rather close safe inspection as the winds help to cool onlookers down a bit. Notice how the molten (red) lava that is flowing cools on the surface. This flow is distinctly pahoehoe (ropey) and it is easy to see how it forms.


Hawaiian shield volcano
Hawaiian shield volcano.
Hawaii's volcanic eruptions are known for their gentleness and resulting shield volcanoes. Fountains and fissures do break out occassionally in the Hawaiian volcanos but these are not the norm.


Lava flow
Lava flow.
New lava flow over road
New lava flow over a road in Hawaii Volcanoes National Park.
Steam from new lava flow
Steam from new lava flow escapes - note yellow markers in background that mark a safe trail for tourists to view the recent lava flows.
Magma turns to lava as molten rock comes to the surface. Molten rock is considered magma when it is under Earth's crust, but when extruded from the crust (as in a volcanic eruption) it is called lava. The lava flows through cracks, vents and fissures, adding to Hawaii's land mass.


Lava cliff
Lava cliff from a recent lava flow.
Fingers of pahoehoe Pahoehoe flow over older, eroded, lava flow
Fingers of pahoehoe lava seem to drip down the lava cliff (left). Pahoehoe flow over older, eroded, lava flow (right).
Pahoehoe lava Pahoehoe lava
Pahoehoe lava hardens into interesting textures.
Glassy surface of new pahoehoe
Closeup of glassy surface of new pahoehoe lava.
Pahoehoe lava has a ropey texture.


Pahoehoe and aa lava flows
Pahoehoe and aa lava flows (above).
Aa lava has a rough and clinkery texture.


Aa Lava Closeup of aa lava
Aa lava flow (left). Closeup of aa lava (right).


Dragon's teeth, Maui
Dragon's teeth, Maui.
Dragon's teeth (in Maui) is a unique lava flow that was influenced by high waves as the ancient lava flow hit the ocean. The wave energy at the time of the flowing lava was strong enough to curl up the edges of the lava before it cooled leaving these unique giant tooth-like structures.


Thurston Lava Tube, Hawaii Volcanoes National Park Small lava tube exposed on a recent flow
Thurston Lava Tube is part of a trail in the Hawaii Volcanoes National Park (left). Visitors enter through a 'skylight' (collapsed roof of a lava tube), walk a ways through the tube and exit via another 'skylight.' A small lava tube (right) that was exposed on a recent flow.
Lava tubes develop as the lava flows and hardens on the outside. The inside continues to flow and may drain out of the 'lava tube' entirely. Some of these lava tubes are small but some are very large (as much as 20 feet in diameter). Many of the lava tubes have a flat bottom as the lava hardened when it slowed down and remind some people of subway tunnels. When the top of a lava tube breaks through it is called a 'skylight.'


Tree Mold Tree Mold with little girl
Tree molds below ground (left) and above ground (right).
Tree molds form as lava flows around living trees. If the lava flow stays deep around the tree it will leave a below grade hole as the tree burns and dies. If the lava flow moves on through it will often leave standing tree molds that are hollow (as the tree burns and dies) but standing above grade because the flow went on past.


Helicopter view of lava flow over road Helicopter view of lava over road and new shelf
Helicopter view of lava flow over road (left). Closer helicopter view of lava over road and new shelf developing on the south shoreline of the big island of Hawaii (right).
New south shoreline of Hawaii, August 2003
New south shoreline of Hawaii, August 2002, as seen from a helicopter.
New acreage is formed in Hawaii when the lava flows make it to the edge of the island. Often this new acreage is just a shelf, with ocean under the shelf so access to this new acreage is off-limits until it is cool and has been explored. If it is solid then it will be safe but if it is just a shelf (with water underneath) then it may break at any time. When the lava flow hits the ocean where there was a cliff before, there may be a step-like feature showing where the old sea cliff was located.


Black sand beach at Punalu'u, southern Hawaii Closeup of Punalu'u's sharp black sand
Black sand beach at Punalu'u, southern Hawaii (left). Closeup of Punalu'u's sharp black sand (right).
Pebbles and sand from Punalu'u
Pebbles and sand from Punulu'u's black sand beach that have been rounded by the waves.
Black sand beaches may form when basaltic lava hits cold ocean water in certain conditions. When this happens the lava explodes, forming sand-sized black chards. These chards are originally very sharp (like broken glass). There are several 'black sand' beaches on Hawaii's south side which have come from this type of event. They are very hard places for sandy beach organisms to live because the sand is sharp and also because the black color tends to get extremely hot at low tide (when the sun is out) and kill marine organisms.


Kaimu black sand beach 1976
Kaimu black sand beach in 1976 (now gone).
Black sand beach may dissappear on Hawaii's southern shores as new lava flows cover them. The famous black sand beach of Kaimu was covered with lava from Kilauea. This used to be one of the most popular tourist black sand beaches and is now under a lava flow.


Black sand beach at Pololu, northern Hawaii
Black sand beach at Pololu, northern Hawaii.
Pololu black sand beach Closeup of Pololu's rounded black sand
Pololu black sand beach (left). Closeup of Pololu's rounded black sand (right).
Not all black sand is from lava hitting the ocean. Black sand beaches may also form from erosion of black volcanic rock. In Hawaii there are a couple of black sand beaches on the north side of the island where raging rivers have cut through black volcanic rock and eroded it. As the eroded rock is carried toward the ocean it breaks up and may form small sediments by the time it gets to the ocean. These pieces of black sand are not sharp because they have been rounded by erosion and the grinding with other sediments on their way to the ocean.


Green sand beach at Mahana Bay, Hawaii
Green sand beach at Mahana Bay, Hawaii.
Lava with olivine deposits Closeup of Mahana Bay's green sand
Lava with olivine deposits (the source of the green sand) (left). Closeup of Mahana Bay's green sand (right).
Green sand beaches may also be from volcanism. In Hawaii a lot of the volcanic eruptions contain olivine, a green glassy-like mineral that forms as a crystal when basaltic lava rises and the temperature increases. At Mahana Bay, along the southern coast of the big island of Hawaii a 49,000 year old tuff ring is eroding along the coastline. Much of this is olivine (containing iron and magnesium) and olivine is heavier than most sand grains. So, as the coastline erodes the olivine stays on the beach longer than most of the rest of the sand (that gets carried away by the waves) and builds up so that the beach appears green. When the tuff ring is fully eroded this green sand beach will disappear. There are only three green sand beaches that I know about - this one, one in Galapagos and one in Guam. Mahana Bay is a good five mile round trip hike along the southern shore of Hawaii (unless you have a four wheel drive vehicle), but well worth the trip.


Red sand beach at Hana, Maui
Red sand beach at Hana, Maui.
Close up of Hawaiian red sand
Close up of Hawaiian red sand
Red sand beaches are rare. This little pocket red sand beach is a short hike (less than five minutes) from the pier at Hana in Maui. It is formed almost entirely from the erosion of a cinder cone that is found at the eastern tip of Maui. The cinders are very red and erode to beautiful red sand. A larger red sand beach is down the road at Kaihalulu.


White sand beach at Hapuna Bay, Hawaii
White sand beach at Hapuna Bay, Hawaii.
White Hawaiian sand, mostly shell Closeup of Hawaiian white sand
White Hawaiian sand is composed mostly of shell fragments (left). Closeup of Hawaiian white sand (right).
Hawaii has exceptional white sand beaches. The white sand on the beaches of Hawaii is almost all broken shell pieces from marine organisms. Pieces of snail shells and coral are common in the white sand. In California the white sand on the beaches has almost no shell material and is primarily composed of light colored minerals from the continental rocks that have eroded and washed to the ocean. Although the white sandy beaches of Hawaii and California may look alike, they are very different. Hawaii's white sand beaches are biological and California's are physical in origin.




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(Revised 29 August 2010)
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