The Hawaiian hot spot
Part of Hall of Planet Earth.
A chain of 107 volcanoes – some islands, some submerged – extends from Hawaii to the northwest. This 6,000-kilometer-long chain begins with the still-submerged Loihi. Moving northwest, the volcanoes become progressively older. The chain forms as the Pacific plate creeps at 9 centimeters a year over a stationary hot spot in the mantle that has been providing magma for 80 million years. The sharp bend records a shift in the plate’s direction of movement that took place 43 million years ago.
Lavas of Hawaii
The Hawaiian lavas are mostly basalt. Basaltic rocks contain high proportions of calcium, magnesium, and iron relative to silicon. For this reason, the lavas are fluid, having the consistency of honey. Instead of erupting in great explosions as Mount St. Helens did, the lavas form slow-moving molten rivers.