Page 91 - (DK) Ocean - The Definitive Visual Guide

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Emergent Coasts Past Change

Emergent coasts occur where land has uplifted faster than the sea has Scientists study past sea-level changes by examining rocks and fossils
risen since the last ice age. The causes are either activity at the edge near shorelines. They also analyze ocean sediments to calculate past
of a tectonic plate or glacial rebound. On emergent coasts, areas that ocean temperatures and climatic properties. Over the past 500 million
were formerly sea floor may become exposed above the shoreline, years, global sea levels have fluctuated by more than 1,000 ft (300 m).
while former beaches often end up well behind the shoreline, or even About 120,000 years ago, sea level was a few meters higher than it is
on clifftops. Sometimes, staircaselike structures called marine terraces today, but some 20,000 years ago, it was 400 ft (120 m) below today’s
are created by a combination of uplift and waves gradually cutting flat level. Most of the rise since then occurred prior to 6,000 years ago.
platforms at the bases of cliffs (wave-cut platforms). Emergent coasts are From some 3,000 years ago to the late 19th century,
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typically rocky, but sometimes they have a smooth shoreline. Examples sea level rose at about / 254– / 127 in (0.1–0.2 mm)
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of these coasts occur on the US Pacific Coast and in Scotland, per year. In the late 20th century, this increased
Scandinavia, New Zealand, and Papua New Guinea. to an average of about ⁄15 in (1.7 mm) per year.
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RAISED BEACH
In this bay in the
Hebridean Islands,
Scotland (left),
the green areas
behind the beach FOSSIL MAMMOTH
are former beaches TOOTH
that have been raised
by glacial rebound
since the end of
the last ice age. New York
THEN AND NOW
The red dotted line
Washington D.C.
on this map shows
NORTH where the east coast
AMERICA of North America was
A TLANTIC 15,000 years ago. At OCEAN ENVIRONMENTS
OCEAN that time, mammoths
roamed on what is
now continental
Miami
shelf—it is not
UPLIFTED CLIFFS uncommon for a
These marine cliffs in Crete, Greece mammoth tooth
(right), have been uplifted by tectonic (above) to turn up in
activity, eroded, and finally tilted from fishing trawls from
the horizontal, also by tectonic activity. these areas.