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In 1943 Winston Churchill, speaking out about rebuilding the British House of Commons, artfully said, “We shape our buildings, and afterwards our buildings shape us.” He was articulating about the buildings and formations in architecture, but his words hold true for the building and formation of islands. Of course, we didn’t build the islands but their distinct character and formations have certainly shaped us. Isn’t it therefore worth exploring how the Big Island, beset with many different coastlines, has developed its unique shape?
Long before humans were even a twinkle in the evolutionary eyesight of Mother Nature, the forces that would govern our lives here on the Big Island were already taking hold. Seventy to eighty million years ago, the Hawaiian-Emperor Chain first emerged as a crumbling mass of molten lava thousands of feet below the surface of the ocean. As the enormous Pacific Plate began to drift northward at a lumbering pace of 3.4 in/year, a “hot spot” of seeping magma from the asthenosphere under the plate began the slow, laborious formation of the Emperor Seamounts and the Hawaiian ridge. At that time, the northern-most atolls in the Hawaiian chain, Kure and Midway, were situated in the present-day location of the Big Island and were much larger than the flat eroded islands slowly sinking beneath the waves that we see today.
Fast forward to present day at the southern most end of this chain, the Big Island gives daily reminders of this million years old island birthing process with the constant explosive flows of Pele’s wrath and the quiet daily rumblings from deep below as the island’s ever growing mass settles onto the Pacific Plate. Laid out over thousands of miles of endless ocean it is apparent to the inquisitive observer that the southern islands, such as Hawai‘i, form towering volcanoes cresting high above sea level. Slowly moving northwest, the height and topography of the islands are torn away by time and the erosive processes of wind, water, and gravity. Eventually, the islands become atolls until they reach the Darwin Point (so named for it was Darwin who first described the life and death of atolls), at which the sea reclaims the land that once broke free of it.
If you’re a resident or visitor to the Big Island, take comfort in knowing that as the youngest member in the group, this process is just beginning to take hold of our island sanctuary. We still have a few million years before anyone will be getting their feet wet. Nonetheless, the balance between virgin terra firma and Mother Nature’s erosive disposition is still shaping this extraordinary island and the people past and present who call it home. Geologically, there are a few colloquial distinctions that every resident is familiar with—the wet side and the dry side, also known as the windward or leeward sides. Although just terminology, they reflect the distinct differences between one coast and another. The Big Island was formed by the eruptions of five shield volcanoes: Hualälai, Kohala, Mauna Kea, Mauna Loa, and Kilauea. The main mass of the island was formed by the world’s heaviest and widest volcano, Mauna Loa. It resides magisterial and majestic 32,000-ft off the sea floor with a base larger than some states. Shield volcanoes are formed from by the basaltic rock they eject. Basalt, as opposed to silica rich magma, creates characteristically gentle sloping sides because the resulting lava is very fluid. Silica rich lava produces thicker shorter flows with beds of explosive ash resulting in steep-sided volcanic islands found elsewhere in the Pacific. The gentle sloping sides of the Big Island contributed to the formation of the coastlines, opened them up for eventual habitation, and added a substantial upland area ripe for agriculture. Once the land took shape, it was scraped and shaped by erosive forces giving different areas of the island distinct topography.