The current eruption of Mauna Loa on the Big Island of Hawaii is part of a long history of volcanic activity that formed the Hawaiian chain and is a vivid demonstration that the giant plates of the Earth’s crust move over time.
If you look at a map of the Hawaiian islands, you will see they form a chain that runs in a northwesterly direction, with Big Island at the southern end of the chain. It is also the only island in the group that is volcanically active.
This chain of islands in the middle of the Pacific Ocean came to the attention of Canadian geologist John Tuzo Wilson who, in 1963, proposed the idea that the islands were created by a very long lasting and extremely hot spot in the Earth’s mantle. His idea was that a plume of molten magma that rises up from deep within the Earth and had punched a hole through the overlying crust.
As the hot lava flows upwards over thousands of years, it builds up into a volcanic mountain that eventually pokes through the ocean surface, forming an island.
This process continues today with the recent eruptions on the summit of Mauna Loa, and with ongoing eruptions on Kilauea, located on the other side of Big Island. In other words, Big Island is getting bigger.
But Wilson saw something more than just the hot spot punching holes in the crust. He saw the Hawaiian island chain as the result of a series of holes based on the fact that rocks on the other islands become progressively older as you go north. Those on Kauai, the northernmost inhabited island, are about five-and-a-half million years old, while those on Big Island are less than one million years old.
He argued that the floor of the Pacific Ocean has been slowly moving northwest, so after one volcano is built, the ocean floor moves over the stationary hotspot and another volcanic island forms. Over millions of years, a chain of islands formed across the ocean. Think of moving a sheet of paper over a candle, where the flame can burn a series of holes through the paper as it moves.
Another hot spot is believed to lay under Yellowstone National Park and is responsible for the numerous hot springs and geysers in the area.
The concept that the floor of the Pacific Ocean is moving provided support to the theory of continental drift, which was hotly debated among geologists right into the 1960s. Wilson was instrumental in developing it further into the current theory of plate tectonics, in which the crust of the Earth is broken into continent-sized pieces that move around, slowly changing the face of the planet.
The current eruption on Mauna Loa is, in geologic terms, sort of a last gasp because a new volcano, Kama’ehuakanaloa — formerly known as Loihi — is forming to the south of Big Island.
It rises more than 3,000 metres above the ocean floor, but its summit is still about a kilometre below the surface of the ocean. It is fed by the same hotspot, so as the Pacific plate continues its slow movement north, Kama’ehuakanaloa could burst above the waves sometime in the future.
The Big Island of Hawaii is a good place to go if you want to see eruptions in action, but eventually, those volcanoes will go quiet. However, if you stick around for another 10,000 years or so, Kama’ehuakanaloa could become the island where people go to see the spectacular sight of the Earth building new land.