An atoll
is a unique type of coral island
formation found in tropical and
subtropical oceans. Atolls
typically form around a volcanic
island over millions of years.
After a volcanic island emerges
from the ocean floor, coral
reefs begin to grow in the
shallow waters around the
island's perimeter. Over time,
the volcanic island slowly sinks
back into the ocean due to
subsidence or erosion. As the
island sinks, the coral
continues to grow upward to
remain near the water's surface.
Eventually, the original island
disappears entirely beneath the
water, leaving only the circular
coral reef structure.
As
illustrated by the first
photograph on this page, atolls
typically form a ring shape,
though some exhibit a
distinctive heart shape. These
unique formations are created by
encircling coral reefs. At the
center of an atoll lies a
lagoon, a body of calm, shallow
water. The atoll next to Bora
Bora is Tupai. To fully
appreciate the spectacular
nature of these geological
wonders, an aerial perspective
is essential.
