The Hawaiian Islands are definitively still expanding because the geological forces that created this archipelago remain active today. This island chain consists of immense volcanic mountains built over millions of years, with their peaks rising from the deep Pacific Ocean floor. The islands are continuously formed by the steady outpouring of molten rock, a geological process unlike the one that creates volcanoes at the boundaries of tectonic plates.
The Driving Force: Understanding the Hotspot
The creation of the Hawaiian chain is explained by the theory of a mantle hotspot. This phenomenon involves a fixed plume of heat and magma rising from deep within the Earth’s mantle toward the surface. The Pacific Tectonic Plate, which carries the entire island chain, is slowly moving in a northwesterly direction over this hotspot.
As the plate slides, new seafloor areas are continually positioned above the magma source. The magma erupts to build new volcanoes, while older ones are carried away from the source, becoming volcanically inactive. Consequently, the islands become progressively older and more eroded the farther they are from the hotspot’s current location.
The youngest and most active volcanoes are clustered directly above or adjacent to the heat source. The hotspot is currently located beneath the southeastern part of Hawaiʻi, often called the Big Island. This model explains why only the Big Island currently features active volcanism and ongoing land expansion.
Evidence of Current Land Accretion
The most measurable evidence of Hawaii’s growth is found on the Island of Hawaiʻi, which is built from five overlapping shield volcanoes. The two most active, Kīlauea and Mauna Loa, are the primary sites of current land accretion.
The steady eruptions from Kīlauea have repeatedly added new acreage to the island’s coastline. During the 2018 eruption, lava flowed into the ocean, creating a large lava delta that added approximately 875 acres of new land to the island’s area. This process of lava meeting the sea cools the molten rock rapidly, building outward and expanding the island’s perimeter.
Mauna Loa, the largest active volcano on Earth, last erupted in 2022, adding new flows that demonstrated the ongoing construction of the island’s bulk. Beyond surface flows, the immense weight and constant magma injection within these volcanoes cause volcanic spreading. This spreading forces the flanks of the volcanoes outward, leading to the accretion of new material at the base of the island as the structure slides seaward over the underlying oceanic crust.
The Next Island in the Chain
The geological process of island building is predictable enough that scientists have identified the next landmass to emerge. This future island is Kamaʻehuakanaloa Seamount, previously called Loʻihi. This active, submerged volcano is located off the southeast coast of the Island of Hawaiʻi and is the newest volcano in the chain.
The seamount rises more than 3,000 meters from the ocean floor, though its summit remains about 975 meters below the water surface. Kamaʻehuakanaloa is actively erupting, building its bulk, a process monitored by the seismic activity it generates. Based on current growth rates, the volcano is projected to breach sea level and become the newest Hawaiian island in a timeframe ranging from 10,000 to 100,000 years.