How Hawaii is formed?

Answer 1

Hawaiian volcanoes primarily erupt a type of rock known as basalt. When molten, basalt produces liquids of relatively high fluidity, compared to volcanoes that erupt more silica rich magma types such as andesite, dacite or rhyolite. The fluidity of molten basalt favors the formation of lava flows, which is why the Hawaiian volcanoes generally have gentle sloping sides. By contrast, lavas with higher silica content are more viscous and commonly produce either thicker, shorter lava flows, thick blocky deposits and/or thick beds of ash that fall from the sky following explosive eruptions. These other types of volcanoes (common outside of Hawaii) are typically steeper sided.

The Hawaiian volcanoes were produced by the Hawaiian hot spot, which is presently under the Big Island of Hawaii.

Answer 2

By volcanic activity.