Sometime around 70 million years ago a cataclysmic rupture occurred in the Earth’s mantle, deep below the crust. A hot spot of liquid rock blasted through the Pacific plate like a giant cutting torch, forcing magma to the surface off the coast of Russia, forming the Emperor Seamounts. As the tectonic plate moved slowly over this hot spot, this torch cut a long scar along the plate, piling up mountains of rock, producing island after island. The oldest of these islands to have survived is Kure. Once a massive island with its own unique eco-system, only its ghost remains in the form of a fringing coral reef, called an atoll.
As soon as the islands were born, a conspiracy of elements proceeded to dismantle them. Ocean waves unmercifully battered the fragile and fractured rock. Abundant rain, especially on the northeastern sides of the mountains, easily carved up the rock surface, seeking faults in the rock and forming rivers and streams. In forming these channels, the water carried away the rock and soil, robbing the islands of their very essence. Additionally, the weight of the islands ensured their doom. Lava flows on top of other lava, and the union of these flows is always weak. This lava also contains countless air pockets and is criss-crossed with hollow lava tubes, making it inherently unstable. As these massive amounts of rock accumulated, their bases were crushed under the weight of subsequent lava flows, causing their summits to sink back into the sea.
What we call the Hawaiian Islands are simply the latest creations from this island-making machine. Someday they will disappear, existing as nothing more than footnotes in the Earth’s turbulent geologic history.
Kaua‘i and Ni‘ihau are the oldest of the eight major islands. Lush and deeply eroded, the last of Kaua‘i’s fires died with its volcano a million years ago. O‘ahu, Moloka‘i, Lana‘i, Kaho‘olawe—their growing days are over as well. Maui is in its twilight days as a growing island. After growing vigorously, Hawaiian volcanoes usually go to sleep for a million years or so before sputtering back to life for one last fling. Maui’s volcano Haleakala has entered its final stage and last erupted around 1790.
The latest and newest star in this island chain is Hawai‘i. Born less than a million years ago, this youngster is still vigorously growing. Though none of its five volcano mountains is considered truly dead, these days Mauna Loa and Kilauea are doing most of the work of making the Big Island bigger. Mauna Loa, the most massive mountain on Earth, consists of 10,000 cubic miles of rock. Quieter of the two active volcanoes, it last erupted in 1984. Kilauea is the most boisterous of the volcanoes and is the most active volcano on the planet. Kilauea’s most recent eruption began in 1983 and and went almost uninterrupted until 2018. Up and coming onto the world stage is Lo‘ihi. This new volcano is still 3,200 feet below the ocean’s surface, 20 miles off the southeastern coast of the island. Yet in a geologic heartbeat, the Hawaiian Islands will be richer with its ascension, sometime in the next 100,000 years.