A


trio of scientists fl oat on the Pacifi c


Ocean. T ey are squeezed together inside a small submersible, preparing to dive. T e sub is 563 kilometers off the coast of Costa Rica. T e men are heading to an underwater mountain called Las Gemelas. T e cramped sub is called the DeepSee.


Sitting in jumpsuits that look like pajamas, the scientists peer out of the sub’s clear dome. It’s like being inside a giant eyeball. When the sub drops beneath the surface,


tiny bubbles stream up all around it. As the sub sinks further, the water gradually turns from a bright turquoise into darker and darker hues of blue. During the descent, a black-and-white manta ray passes by. It looks like an enormous bat gliding through the water. Las Gemelas looms below. Like most


seamounts, the top of this underwater mountain is below the ocean’s surface. By the time the sub reaches the top of Las


Gemelas, the water pressure is 18 times greater than at the surface. At 213 meters deep, there is little light. T e sub’s bright lights shine on a carpet of corals, sea fans, and sponges. A video camera catches schools of fi sh


swimming by. A pair of lasers creates parallel lines a third of a meter apart, forming a grid. T is grid helps the scientists measure the things they see. A 4-meter prickly shark seems to stop and pose for the camera. T e scientists set the sub down


inside a large crater on top of the mountain. T ey turn off the lights of the sub.


T ey sit in total darkness. T ey only


have minutes to take readings and make observations before they are forced to surface again. One of the scientists releases water stored inside the bottom of the sub. It keeps the sub stable underwater. T is water, called ballast, creates bubbles that race toward the surface. As the sub rises, the bubbles collide with


tiny creatures called plankton. T e plankton respond by lighting up. It’s a beautiful end to a fantastic dive.


Volcanic Peaks


Seamounts are found throughout the world’s oceans, though most of them are found in the Pacifi c. To be defi ned as a seamount, the land must rise at least 1,000 meters above the surrounding seafl oor. Some of these underwater mountains are more than 4,000 meters tall! Seamounts are most oſt en the remains of


extinct volcanoes. T ey appear either as isolated peaks or as part of a chain. T ey’re oſt en seen near “hotspots” in the oceanic crust. Beneath these spots, melted rock, called magma, bubbles. For example, the Hawaiian Islands formed over a hotspot. T e Emperor Seamount chain is part of these islands. T is chain is made up of more than 80 undersea volcanoes. It stretches more than 5,800 kilometers. T e Atlantic Ocean has a chain of seamounts, too. T e New England Seamount chain stretches for 1,000 kilometers. It has more than 20 volcanic peaks.


This seamount teems with life.


12


NATIONAL GEOGRAPHIC EXPLORER


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