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Kauai Geology


Is Kauai moving and when was its last eruption? Yes, although very slowly, due to the northwest movement of the Pacific Plate (about 3-1/2″ a year), it has moved about 311 miles over the last 5 million years. It is believed that about 5 million years ago Kauai was where the Big Island is now. The last set of eruptions on Kauai occurred between 1.41-1.43 million years ago and are post-erosional eruptions known as the Kola Volcanic Series.

How old is the Na Pali and when did it form? The Na Pali, depending upon which section you date (potassium-argon method), ranges in age from 4.44 to 5.72 million years old and it is a part of the Waimea Canyon Volcanic Series of Eruptions. Kauai consists of a single great shield volcano which is deeply eroded and partly veneered with much later volcanics. The Kauai shield rises 17,000 feet above the ocean floor. At the top of the shield (centered at Mt. Waialeale) is a caldera 12 miles across – the largest in the Hawaiian Islands. Inside this caldera is the Alakai swamp, the highest elevation swamp in the world. A caldera forms when the mountain’s summit collapses it is a deep depression, much wider than deep, which is formed as the summit sinks in upon itself, compressing earlier layers of lava flow. The Waimea Canyon Series is a part of the portion that built the main mass of the shield outside the caldera known as the Na Pali Formation. The Na Pali was named “many cliffs” because of their exposures along the Na Pali Coast.

When were the different islands formed? Moving up the island chain from the southeast (the Big Island) to the northwest (Kure Atoll-oldest of the 200 or so Hawaiian volcano islands-it is 28-million years old) each of the Hawaiian Islands is generally older than the next. In fact, the chain continues beyond Kure as a series of now submerged former islands known as the Emperor seamounts. The Emperor Chain extends almost directly north 1,454 miles from Daikakuji Seamount to Meiji Seamount. The age of Meiji Seamount, about 75-80 million years, attests to the longevity of the Hawaiian hotspot.

Why are the newest of the Hawaiian Islands the largest? Is tectonic movement (movement of the earth’s crust) slower now than it once was, or is the hotspot more active now? Careful analyses of the volume of lava erupted by the plume or hotspot as a function of time show clearly that the youngest islands are the biggest. Along the entire length of the Hawaiian-Emperor chain, there are periods of high apparent eruption rate alternating with periods of low eruptive volumes. The idea that the Pacific Plate velocity could be the reason, can be ruled out because periods of slow motion don’t correspond with the bulge or increase in volume. Possibly, the output of the hotspot changes with time, but this is difficult to prove or disprove. Most theories of plumes and experiments by fluid dynamicists predict a steady output or blob-like output, but these are simple models. The differences in volume or output of the hotspot are essentially unexplained. Scientists don’t know much about how plumes or hotspots work but apparently the volume of melted rock they produce can vary with time.

What is Loihi? – Is it the newest volcano island being formed that is still under the sea? Yes, Loihi Seamount, sometimes known as the “youngest volcano” in the Hawaiian chain, is an undersea mountain rising 11,538ft. above the floor of the Pacific Ocean. Both Loihi and Kilauea volcanoes sit on the flank or side of Mauna Loa volcano an older, larger and still active volcano on the Big Island. Loihi sits submerged in the Pacific off of the south-eastern coast of the Big Island. Although hidden beneath the water, Loihi is nevertheless, taller then Mt. St. Helens was prior to the eruption in 1980. Before the late 1970’s, Loihi was not known to be an active volcano. It wasn’t until an earthquake swarm occurred that spurred an investigative expedition revealing Loihi as being a young, active volcano, and not an old dead seamount, as was previously thought.

What is happening right now with Loihi? The largest swarm of earthquakes ever recorded on any Hawaiian volcano shook Loihi Seamount. The swarm began on 7/17/96; to date a total of 4,000 earthquakes have been recorded by the Hawaii Volcano network.

How have the Hawaiian Islands changed over time-besides moving northwest to make room for the next island to be formed? Kauai and Niihau formed two separate islands that coalesced as Kauai grew, but later they separated to become separate islands once again as they subsided (sink into the ocean). It is thought that Kauai used to be over 9,000 feet at it tallest point; today it is just over 5,243 feet at its highest point.

One million years ago, the Maui Nui island was over the hotspot which is now 4 separate islands; Molokai, Lanai, Maui, and Kahoolawe. These volcanoes that comprise the Maui Nui complex were at one time joined by land bridge with a minimum elevation of 3,500 feet.

Geology Update: How did the Hawaiian Volcano Islands form?  Each of the Hawaiian islands formed over a “hotspot” (about 21 degrees north of the Equator). A hotspot is the result of a persistent region of molten or melted rock known as magma. There are at least 50 hotspots world wide and they occur at several places beneath the moving plates of the earth’s crust. The earth’s crust is divided into a dozen or so moving plates called tectonic plates-the plate that is over the Hawaiian hotspot is named the Pacific Plate. The tectonic plates are adrift on the molten magma beneath. The Pacific Plate is currently moving northwest about 3-1/2″ per year. Thus when a volcano forms over the Hawaiian Hotspot, it is eventually pulled northwest and becomes extinct (i.e. Hawaiian Islands). In this way, a chain of volcanoes is produced.

Melted rock or magma generated from the hotspot rises buoyantly because it is lighter than the surrounding rocks Earthquake patterns suggest that the magma rises up through cracks in the tectonic plate, piercing the earth’s crust and erupting onto the seabed floor. When a submarine volcano grows tall enough to rise above the ocean’s surface it becomes an island – this is how all of the Hawaiian Islands were formed. The Big Island (Mauna Loa) rises up 32,000 feet from the ocean floor (making it the largest mountain on Earth) though only the top 13,800 feet are above sea level.

Ring of fire – Hot Spot or Not? Hawaii is in the center of the Pacific Plate, surrounded on all sides by subduction volcanoes. These occur when one plate “subducts” beneath another creating tremendous pressure which is released via volcano vent. Volcanoes all around the edges of the Pacific Plate form what is known as the Pacific Ring of Fire. These Pacific Rim volcanoes include Japan, New Zealand, Alaska, and Pacific Northwest, (i.e. Mt. St. Helens), South America. But Hawaiian Vocanoes are unique!