Page 186 - (DK) Ocean - The Definitive Visual Guide

184 THE OPEN OCEAN AND OCEAN FLOOR

The Ring of Fire SAFE HAVEN

All around the margins of the Pacific Ocean, tectonic plates are colliding.
This produces a belt of intense volcanic and earthquake activity Mid-ocean-ridge islands
encircling the Pacific, known as the Ring of Fire. It extends for 18, 600 offer protected breeding
places for many sea
miles (30,000 km) in a series of arcs, from New Zealand, through Japan, birds, with rich feeding
and down the west coast of the Americas to Patagonia. About three- provided by upwelling
quarters of the Pacific lies over a single plate, the Pacific Plate, which is currents offshore. The
colliding around its edges with the North American, Australian, and sooty tern is found in all
various minor plates. In the eastern Pacific, the smaller Cocos and Nazca tropical seas. It nests
plates are colliding with the Caribbean and South American plates. As on oceanic islands.
Ascension Island
the edges of the Pacific, Cocos, and Nazca plates subduct (move down) once provided safe nesting
beneath the younger, less dense edges of neighboring plates, massive for 50,000 pairs, until humans
slabs of rock shatter explosively along faults, producing earthquakes. introduced rats and cats, more than
A series of deep ocean trenches, arranged in arcs around the Ring of halving the sooty tern population.
Fire, mark the boundaries where the subducting plates move beneath
neighbouring plates. Parallel to these trenches—typically at a distance of
100 miles (160 km) and always on the side of the overriding plate—are
arcs of often highly active volcanoes, taking either the form of volcanic THE RIDGE ON LAND
islands or (on the eastern side of the Pacific) forming lines of volcanoes For most of its vast length, the Mid-Atlantic
on land, such as the volcanoes of Central America. Ridge is hidden deep beneath the ocean.
However, at Iceland, where both the Eurasian
and North American plates are separating,
it rises above the surface.
A R C T I C O C E A N

NORTH
A SIA AMERICA

P A CIFIC A T L A N T I C
SOUTH
OCEAN AMERICA
INDIAN O
OCEAN AUSTRALASIA A N C
E

S O U T H E R N O C E A N

HOTSPOTS OF VOLCANIC ACTIVITY
Red on this map shows areas of volcanic activity
around the Pacific Ocean, highlighting the Ring
of Fire. These volcanoes form on continental
plates as oceanic plates are thrust below.

OCEAN ENVIRONMENTS MOUNT ST. HELENS

Mount St. Helens in Washington is part
of the Ring of Fire. It erupted in May 1980,
blowing the whole top off the volcano.
Here, in 2004, a new lava cone has
begun to grow, producing steam.