Kaua‘i landscape window to the past

Kaua‘i’s spectacular scenery makes it a top destination for tourists from all over the world. It has been the backdrop of choice for many popular movies, including the Jurassic Park series and the 1970s remake of King Kong. Although you almost expect to see T-Rex crashing around in the lush green rainforests and deep valleys, the island of Kaua‘i was actually not born until around 5 million years ago. Since then, it has undergone major geologic changes, some sudden, some gradual, which have sculpted it into the island we see today.

Although Kaua‘i is the oldest of the eight major Hawaiian Islands, it is a young member of the Hawaiian-Emperor Chain. The islands (and submerged seamounts) were formed when the Pacific Plate of the Earth’s crust moved over a hot spot. Island formation has been occurring over this hot spot for at least 80 million years. Over time, the island chain gets longer as more islands are formed.

The life cycle of a Hawaiian shield volcano is made up of an initial submarine phase (Lo`ihi, off the southern coast of Hawai‘i, is in this stage). This is followed by a highly active shield-building phase (for example, Kilauea and Mauna Loa). The production rate of lava drops, following this phase, and the erupted lava becomes slightly different in composition (Mauna Kea is in this stage now). After a pause, the volcano enters a rejuvenated phase, when small eruptions of more evolved lavas take place.

Once the islands form, they are progressively destroyed. The destructive phase can last for 75-80 million years. It has been taking place for just 3-4 million years on Kaua‘i, and already it has immensely altered the island. The dominant slow-acting forces changing Kaua‘i are erosion and island subsidence. Subsidence occurs when the crust, on which the island sits, cools and compacts. Erosion – the weathering and transport of material from upland to lowland areas and into the sea – occurs mainly through the action of rain and wind. In another 2-3 million years, Kaua‘i will be reduced to the size of Nihoa, the next older Hawaiian island to the northwest.

The shape of Kaua‘i has also been dramatically modified by large, rapid, dynamic geological processes. During or after shield formation, giant landslides, caldera collapse, and complex faulting occurred which greatly altered the landscape and made it vastly more complicated for geologists coming along later to interpret the rocks.

The Na Pali coast, on the north shore, comprises some of the most stunning scenery on Kaua‘i, with huge cliffs, knife-like ridges, and deep canyons. The lava flows that make up this part of the island, the Waimea Canyon basalt, were erupted during the shield-building stage of volcanism. Many geologists think that the steep cliffs here could only have been formed when large chunks of the volcano’s flanks slid into the sea, leaving deep scars, which were further eroded into their present form by the weather and ocean waves.

A caldera complex was formed in the centre of Kaua‘i when the top of the shield collapsed. The structure is 10-12 miles across, the largest in the Hawaiian Islands. It was filled in by later lava flows, called the Olokele Formation. These flows ponded in horizontal layers that cooled slowly, making them thicker and more erosion-resistant. Over time, they weathered and eroded, and soils and vegetation developed. The result is two of Kaua‘i’s most spectacular landmarks: eastern Waimea Canyon and one of the highest bogs on Earth, the Alaka`i Swamp.

The Alaka`i Swamp is a place like no other. High rates of rainfall, runoff from Mount Wai`ale`ale (which receives a staggering 430 inches of rain per year!) and poor drainage give rise to the saturated bog conditions. Stunted native trees and very rare Hawaiian forest birds can be found in this remote part of Kaua‘i.

The net result of all of these geologic processes is that, as the Hawaiian Islands age, they become smaller and more deeply incised. Kaua‘i serves as an excellent example of an aging ocean island and shows us, through its geology and morphology, its entire life cycle.

Activity Update

Eruptive activity at Pu`u `O`o continues. Several vents within the crater glow intermittently on clear nights. The Pu`u `O`o crater web-camera is offline for repair.

The PKK lava tube continues to produce intermittent surface flows from the top of Pulama pali nearly to the ocean. All three ocean entries that were active a week ago had died by April 13. Numerous surface flows were active on the coastal plain, however, and one had nearly reached the sea cliff at Highcastle on the 13th. The closest activity to the end of Chain of Craters Road, in Hawai‘i Volcanoes National Park, is at Highcastle, 3.7 km (2.3 miles) from the ranger shed. Expect a 1.5-to-2-hour walk each way and remember to bring lots of water. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.

During the week ending April 13, one earthquake was felt on Hawai‘i Island. A magnitude-2.6 quake occurred 3 km (2 miles) south of Kapoho at a depth of 0.4 km (0.2 miles) at 8:55 p.m. on Tuesday, April 12; it was felt at Leilani Estates.

Mauna Loa is not erupting. During the week ending April 13, eight earthquakes were recorded beneath the summit area. Two were deep and long-period in nature. Inflation also continues beneath the summit.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by HawaiiNews.com with permission.

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