Maui Nui: 4 Islands Connected

Everyone knows that the ‘Big Island’ is the biggest island of the island chain, but what if Maui were once 50% bigger, with the combined expanse of at least seven volcanoes? 1.2 million years ago, the island of Maui was connected to Moloka’i, Lana’i, and Kaho’olawe, creating what is known as Maui Nui (Big Maui).

The oldest volcano of Maui Nui has long been submerged in water. The Penguin Bank sea shoal is connected to Moloka’i in the West, reaching towards O’ahu. It began as a shield volcano 2.2 million years ago and was once connected to O’ahu, however briefly. It likely covered eight times the area of Kaho’olawe. Now, coral lives at the top of the once-active volcano at less than 200 meters below sea level.

After Penguin Bank came West and East Moloka’i, Lana’i, West Maui, Kaho’olawe, and finally Haleakala, serving as the youngest island to be a part of Maui Nui. Maui Nui covered about 14,600 square kilometers (5,640 square miles), making it indeed 50% bigger than the Big Island.

But how do scientists know that these islands were once connected? In 1963, the idea of a hotspot was first proposed by Canadian geologist J. Tuzo Wilson. The idea is that there’s a spot in the Pacific tectonic plate that sort of leaks lava. Because the tectonic plate moves pretty slowly, even compared to volcanoes, enough time passes with the hotspot in about the same location for a volcano to eventually form above sea level.

It was a good hypothesis, but it needed to be confirmed. The hypothesis suggested that the northwestern islands should be progressively older. By testing the amount of argon in volcanic rocks, geologists can measure how old the rock is. New volcanic rock has no argon but has plenty of a radioactive form of potassium. As time passes, the potassium decays into argon. The oldest islands had more argon in their rocks than the newer islands.

This was not the only evidence for the hypothesis. As volcanic islands get older and time passes, they start to erode and subside, caused by the volcano’s weight pressing back into the sea floor. This quickly added evidence to Wilson’s hypothesis; Mauna Kea is the tallest mountain from the sea floor, and seamounts farther Northwest are over 2 kilometers underwater.

Maui nui went through the same process. As the island sank into the ocean and the sea levels

rose, the island was split into four, and Penguin Bank was completely submerged. 700,000 years ago, East Moloka’i permanently split from West Maui, though the islands were still connected through Lana’i. Then, 100,000 years later, the connection between East Moloka’i and Lana’i sank underwater, only emerging when sea levels dropped.

It was only about 18,000 years ago that glacial melting finally split the island into the four that we know today.

And it won’t stop there! At present rates, in another 10,000 to 20,000 years, Haleakala and West Maui will become separate islands. The same thing will likely happen to the Big Island—though that’s a long time from now—and another island will continue the chain as the hotspot moves across the globe.

Sources:

About the hot spot: https://www.ncbi.nlm.nih.gov/books/NBK208869/

About Maui Nui: https://www.usgs.gov/news/volcano-watch-geologic-tour-hawaiian-islands-maui

More on Maui Nui: https://www.usgs.gov/news/volcano-watch-once-big-island-maui-county-now-four-small-islands

About Maui Nui + Flora and Fauna: https://activityauthority.com/maui-nui-defined/

Hawaii Islands Map Including Underwater: https://pubs.usgs.gov/imap/2809/pdf/i2809.pdf