Hawaii geography and landscapes
Volcanic origins and activity
The Hawaiian Islands are all colossal volcanoes peaks born in the depths of the Pacific Ocean, above a crack in the earth's crust. For 70 million years, this "hot spot", as geologists call it, has been spitting out magma. When, rising from the bowels of the earth, it comes into contact with the bottom waters of the Pacific, it freezes in “basalt cushions”, kinds of natural cannonballs that pile up. As long as the lava flow does not dry up due to the movement of the continental plates, the pile ends up reaching the surface, giving rise to an island.
The whole archipelago was born like this. Depending on the case, 90% to 99% of the mass of volcanoes that formed the Hawaiian Islands are submerged!
With the ocean floor drifting with the Pacific plate, only the hot spot remains stationary. The islands, carried along in the movement, sail towards Japan at a speed of 8,5 to 9 cm per year, as if drawn on a gigantic conveyor belt. The Hawaiian Islands are aligned, over 2 km, on a south-east-north-west axis corresponding to the direction taken by the plate. Gradually moving away from the nurturing hotspot, the volcano forming the island dries up, eventually freezing. Then begins a long work of undermining.
As soon as the magma stops feeding it, the islands, delivered to the forces of erosion, begin to be consumed. They regularly collapse in formidable landslides. From the south-east to the north-west, each island thus forms a step back in time, increasingly older as one moves away from the hot spot.
The dean, Kure, which appeared 35 million years ago, only survives as a vestige atoll. The mountains have disappeared there, giving way to a lagoon surrounded by a coral reef dotted with a few islets - made up of the time when the central island still existed. Soon, the continental drift, crossing "Darwin's Point", will drag the atoll into waters too cold for the survival of the coral, condemning it to disappearance.
The Big Island of Hawaii
At the other end of the archipelago, the Big Island of Hawaii, next to the hot spot, continues to be supplied with magma. Its volcanoes are accumulating records.
Le Mauna loa, which appeared again in 1984, is the largest active volcano on the planet, 70 times larger than Etna! Culminating at an altitude of 4 m, it actually measures 170 m measured from its oceanic base!
But it is now the Kilauea which spits out the most lava. In an almost uninterrupted eruption since 1983, it flows through a whole network of craters and faults, sometimes by large lava fountains, more often by discrete flows which do not cease to extend the surface of the Isle. In a few centuries or millennia, it will in turn cease to be fed.
But 40 km off the island, Loihi is growing. The volcano is expected to pierce the water surface within 10 to 000 years.