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.