Holo Holo Blog

Have you ever looked around at the endless, expansive beauty of Kauaʻi and wondered how the landscape has come to look like this? What occurred to cause such jaw-dropping scenery, including deep caverns, cliffs, canyons, valleys, coastlines, and more?

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Kauaʻi is home to some of Earth’s most dramatic and diverse landscapes. Today, we take you for a quick tour of the geological history of Kauaʻi, the Garden Isle of Hawaiʻi.

What is Geological History?

Geological history studies the Earth’s formation, history, and evolution, including continents, oceans, atmosphere, and biosphere. The history of Geology relies heavily on the record of time found in layers of rock to study the origin, development, and changes of Earth and its landscapes over time. (1)

The Hawaiian-Emperor Seamount Chain

The Hawaiian islands are part of the Hawaiian-Emperor Seamount Chain, an underwater mountain range of islands, seamounts, atolls, shallows, banks, and reefs. It is comprised of over 80 underwater volcanoes and stretches 3,900 miles from the Aleutian Trench off the coast of the Kamchatka Peninsula to the Kamaʻehuakanaloa Seamount, the youngest volcano in the chain, which lies about 22 miles southeast of the Big Island. (2)

What we know about the origin of Kauaʻi:

• The Pacific Plate, a mass tectonic plate deep in the ocean, shifted over a magma plume and pierced the Earth’s crust, providing a pathway for magma to flow.
• The hot magma shot up with incredible pressure from the Earth’s crust, forming the volcanoes that created the Hawaiian Islands.
• Kauaʻi and Niʻihau (the oldest Hawaiian islands) volcanoes formed about 6 million years ago. They differ from the rest of the Hawaiian islands in that they are individual volcanoes rather than a combination of conjoining volcanoes.
• Mind-blowing fact: The mountains we see in Hawaiʻi are a mere fraction of the actual size of the volcanic mountains. Are you ready for this? 98.5% of the island chain sits below sea level. (3, 4, 5, 6)

Four Stages to the Growth of the Hawaiian Volcanoes

Harold Stearns, a USGS (United States Geological Survey) Geologist accredited for mapping the majority of Hawaiian Islands in the 1930s-40s, reveals four stages to the growth of the Hawaiian volcanoes: preshield, shield, postshield, and rejuvenated. (7)

According to Stearns:

• Preshield (or submarine) is when a volcano starts slowly growing underwater.
• Shield occurs when eruptive activity is frequent, and the volcano rapidly builds above sea level.
• Postshield occurs when the volcanic activity starts to wane, and erosion outpaces resurfacing by lava.
• The rejuvenated stage is when infrequent, isolated, and small eruptions might occur up to millions of years after the postshield stage ends. (8)

The powerful shield stage of Niʻihau and Kauaʻi volcanoes ended about 4 million years ago. Soon after, in the postshield stage, volcanic eruption subsides, and erosion occurs, carving the deep canyons and striking cliffs into the landscapes we see today. While every Hawaiian island went through the first two volcanic stages, Niʻihau and Kauaʻi went through all of the stages and are still in the rejuvenated stage today. (9)

USGS reveals that:

On Kauaʻi, rejuvenated volcanism has occurred more or less continuously for the last 3.5 million years. The most recent eruption was only 150,000 years ago in the south part of the island, where black rock around the blowhole near Poʻipū and cinder cones around Kōloa look similar to young volcanic rocks on the Island of Hawaiʻi. In fact, these eruptions are young enough to suggest that rejuvenated volcanism on Kauaʻi is not yet over, but the odds of future eruptions in our lifetimes are small. (10)

A Window in Time

Historical Geology is a fascinating, in-depth study that helps us identify the world around us and how it came to be. It is a window into the world of scientific wonder, a window in time, if you will. By looking back, we can make sense of what we see now and apply that knowledge to the future.

(1): https://www.britannica.com/science/geologic-history-of-Earth/Development-of-the-atmosphere-and-oceans

(2): https://en.wikipedia.org/wiki/Hawaiian%E2%80%93Emperor_seamount_chain

(3): https://education.nationalgeographic.org/resource/chain-islands-hawaiian-hot-spot/

(4): https://www.usgs.gov/news/volcano-watch-geologic-tour-hawaiian-islands-kauai-and-niihau

(5): https://www.teok.com/book-kauais-geologic-history/

(6-10): https://www.usgs.gov/news/volcano-watch-geologic-tour-hawaiian-islands-kauai-and-niihau

Content Creation by Jessica Stein