The Geology of Hawaii

Hawaii

The Royal Hawaiian Waikiki Beach
Waimea Bay

When you visit Hawaii it doesn’t take very long to realize you have come to a place like no other on earth. Isolated from continental land by at least 2,400 miles of ocean. It is blessed with year round average temperatures in the eighties and abundant rainfall. Its history is both ancient as well as recent. First populated by the Polynesians over fifteen-hundred years ago it was not discovered by the European explorers until January, 1778, when the English explorer Captain Cook set foot ashore. The native Hawaiians speak a language unique to them and proof of this is everywhere from highway signs to greetings from the locals. Because of Hawaii’s isolation the flora and fauna are a blend of unique as well as introduced species from all around the world. Modern Hawaii has also the most ethnically diverse population found anywhere with seven races each representing over five percent of the population. This includes the Polynesians, Asians with Japanese being the largest segment, whites, Filipino, Blacks, Hispanics with twenty-one percent of the population being of mixed race decent. Even the geology and origins of this island chain are unique. Welcome to paradise…

The shore at Lanai Lookout, Oahu

Hawaii – a Geological Wonderland

Most of the earth’s islands are found at tectonic plate boundaries either from spreading centers (like Iceland) or from what are called subduction zones where one tectonic plate slides under another (like the Aleutian Islands). Hawaii is geologically unique because it is caused by a ‘hot spot.’

Illustration from the Jaggar Museum, Hawaii

 

There are a few ‘hot spots’ on earth and the one under Hawaii is right in the middle of the Pacific Plate, one of the earth’s largest crustal plates. A geologic ‘hot spot’ is an area under a crustal plate where volcanism occurs. It is easy to geologically explain volcanism at plate spreading centers and subduction zones but not as easy to explain a ‘hot spot’ where molten magma breaks through the crustal plate. (Some theories describe this as a particularly hot part of the molten magma).

Another hot spot under the American plate is Yellowstone National Park with its geysers and other thermal features. The Hawaii hot spot is under the seafloor producing undersea volcanoes. Some of these volcanoes build up to the surface of the ocean and become islands. Over millions of years the plate moves across the ‘hot spot’ and the original volcanoes become extinct and new volcanoes begin to form in the area of the ‘hot spot.’

Understanding all of this explains why in the Hawaiian islands, the more southeast you go, the more active the volcanoes are. This shows that the plate is moving northwestThe island farthest south is the big island of Hawaii with no fewer than five volcanoes with some active most of the time. The farther north you go, the islands are older and the more time erosion has washed away the land. Niʻihau is the largest and last lightly inhabited island before the ten islands and atolls in the uninhabited Northwestern Hawaiian Islands.

He iconic profile of Diamond Head east of Waikīkī Beach on the island of Oahu is the crater of a long extinct volcano.

Hawaii – The Big Island

Volcanoes of the island of Hawaii, Illustration from USGS exhibit

Kīlauea

The three largest volcanoes on the big island are Kilauea, Mauna Loa and Mauna Kea. Volcano National Park encompasses Kilauea with a number of different volcanic features.

Picture caption: 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).

Halema’uma’u crater

On a recent visit to the big island we went up to Kīlauea. The caldera was shrouded in rain and fog so we didn’t have an opportunity to see much but we did get to Halema’uma’u. We spent time at the USGS museum and also hiked thru the Thurston Lava Tube.

Thurston Lava Tube

Thurston Lava Tube is part of a trail in the Hawaii Volcanoes National Park. Visitors enter through a ‘skylight’ (collapsed roof of a lava tube), walk a ways through the tube and exit via another ‘skylight.

Lava & sea at the edge of creation

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 hardens when it slows down and look like subway tunnels. When the top of a lava tube breaks through it is called a ‘skylight.’

Midnight off the southeast coast of Hawaii

Due east of Kilauea, lava from Pu’u O’o volcano travels downhill for miles in lava tubes to reach the ocean where it spills out along the shoreline creating large clouds of steam and volcanic gas. Our cruise ship crossed around the southern coast at night and around midnight moved to within one mile of the lava flows as they poured into the ocean. Viewing the display at night from the sea is an awesome event. There are also trails that allow hikers to get down near the area where the lava spills into the sea but we’ve been told that the hike down and back can take most of the day.

In addition to the volcanoes on the island of Hawaii there is a new eruption just south of the island called Loihi. This volcano has been erupting from the sea floor and currently its peak is at a depth of 3,000 feet. At its present rate of growth it will probably break the surface of the Pacific after another 10,000 years.

Maui

Looking down from 10,000 feet up on Haleakala

 Haleakalā Volcano

The summit of Haleakala
Haleakala

Haleakala is home to the highest peak on Maui, at 10,023 feet. It also holds the world record for climbing to the highest elevation in the shortest distance- a mere 38 miles from sea level to the top! Because Maui is north of Hawaii the volcanic activity is dying down. It is believed that the last major eruption was in the seventeenth century with only a few smaller events in the twentieth century. The USGS lists the eruption risk now as normal. A Normal status is used to designate typical volcanic activity in a non-eruptive phase.

We visited the top of Haleakalā a couple of years ago and it is almost like traveling to another planet: bare peaks and slopes covered in a spectrum of colored rock, dirt and sand. Clouds hung near the slopes with vistas across the crater* that stretch on forever and views back across the island are breathtaking. The drive to the top of the volcano is an adventure in itself as the road snakes back and forth up the slope with temperatures dropping as you ascend and winds blowing as you reach the summit.

O‘ahu

The profile of Diamond Head on O‘ahu is the western rim of an extinct volcano and is perhaps one of the most recognized volcanic mountains on earth. In addition to Diamond Head there are a few additional extinct vulcanoes on the island including Hanauma Bay, Koko Head, Punchbowl Crater, Mount Tantalus and Aliapa’ak.

Diamond Head

Throughout the Hawaiian islands the high and jagged peaks catch the tropical trade-winds causing huge amounts of rainfall. This micro-climate results in a lush landscape crossed with rushing streams and dotted with beautiful waterfalls. The islands are noted for their vertical cliffs, isolated valleys, incredible beaches and acres of farm land. This tropical climate and rich soil yields plentiful cash crops that include pineapples, macadamia nuts, coffee and cacao nibs used for making chocolate. Welcome to paradise…

 

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One thought on “The Geology of Hawaii”

  1. Thank you for this wonderful summary of Hawaii. So sorry we missed this trip. I’m sure you will go back and maybe we will be able to go along next time.

    Like

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