How Did Hawaii Form?


Hawaii sits in the middle of the Pacific Ocean,
and nowhere near the edge of a tectonic plate where volcanoes are usually found. So how did the island chain form, with all of its volcanoes? The island chain is located over a hotspot fueled by a mantle plume of heated rock. Solid rock at the bottom of the Earth’s
mantle is heated by the planet’s core. That hot rock slowly rises and pushes up the
crust, forming a bulge. Under that bulge, some of the rock melts into
magma. Magma makes its way to the surface through
cracks in the crust. Once it’s above ground, it’s known as
lava. Hawaiian volcanoes produce lava flows made
of melted basalt, which is more liquid than lava produced by more explosive volcanoes
like Mt. Saint Helens. Basaltic lava flows form volcanoes with gently
sloping sides. A lake of liquid lava can sometimes be seen
at the top of active volcanoes, like Kilauea. [spraying sound]
Sometimes the magma can flow underground to the sides of the main vent and erupt out of
cracks in the ground called fissures. When lava meets ocean the island grows, but
you may not want to get too close. That steam is hydrochloric acid laced with
tiny shards of volcanic glass. The Pacific plate is moving to the northwest,
dragging the crust over the hotspot and creating islands as it goes. The hotspot itself might be moving too. The volcanoes on Niihau and Kauai, the northwesternmost
islands in the chain, are about five million years old. The big island of Hawaii is the youngest and
started forming about 400,000 years ago. It’s still changing, and is home to four
active volcanoes. Eventually the big island will no longer be
over the hotspot, and a new island will grow next to it. But maps won’t need updating for a while
– Loihi won’t break the ocean’s surface for another 200,000 years, give or take. For Scientific American, I’m Kelsey Kennedy. [music]