Placeholder Image

字幕列表 影片播放

  • 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 whileLoihi won't break the ocean's surface

  • for another 200,000 years, give or take.

  • For Scientific American, I'm Kelsey Kennedy.

  • [music]

Hawaii sits in the middle of the Pacific Ocean, and nowhere near the edge of a tectonic plate

字幕與單字

單字即點即查 點擊單字可以查詢單字解釋

B2 中高級 美國腔

夏威夷是如何形成的? (How Did Hawaii Form?)

  • 142 13
    cgw0814 發佈於 2021 年 01 月 14 日
影片單字