Page 83 - (DK) Ocean - The Definitive Visual Guide

81

ATLANTIC OCEAN NORTHEAST a day, some 105 billion gallons
(400 billion liters) of water roar
Saltstraumen through this strait on the flood
tide, reaching maximum speeds DANGEROUS WATERS
FEATURES of up to 25 mph (40 km/h), as When the tidal race flows, the spinoff
Tidal race and small tidal forces act to fill the 30-mile- vortices, which can be 33 ft (10 m) across,
whirlpools
(50-km-) long Skjerstadfjord. are capable of pulling objects down to the
TIMING Twice a day, the waters flow out rocky bottom of the channel.
Four times daily
again through the same channel.
The flows of water, and associated
LOCATION Between Saltenfjord and Skjerstadfjord, whirlpools, are equally strong
northwest coast of Norway
during the ebb as the flood tide.
Despite Saltstraumen’s ferocity, the
The Saltstraumen tidal race occurs channel is regularly used by
on the northwest coast of Norway shipping. For short periods every
and is generally acknowledged to be day, the tidal flows slow almost
the strongest and most extreme tidal to a halt, allowing large vessels
current in the world. It forms at a to pass safely into and out of
bottleneck between the Saltenfjord, Skjerstadfjord. Smaller vessels
an inlet from the Norwegian Sea, and do remain at risk from residual
the neighboring Skjerstadfjord: its underwater currents during
driving force is a difference in sea level these periods of “slack water,”
of up to 10 ft (3 m) that develops four but many experienced pilots still
times a day between the two bodies of venture out. Saltstraumen offers
water. The channel at the center of the both interesting opportunities for
bottleneck—Saltstraumen itself—is a divers and excellent angling (see
2-mile- (3-km-) long strait between panel, below). Incoming tides
two headlands, with a width of just carry large amounts of plankton
500 ft (150 m) and a depth that varies through the channel, and fish of
from 65 to 330 ft (20 to 100 m). Twice various sizes follow.

DISCOVERY
LIFE BENEATH THE WHIRLPOOLS

It is possible to dive into and explore the Saltstraumen,
although this can safely be attempted only when the tidal
streams are at a minimum. Divers have discovered
rich and colorful marine life at the bottom of
the channel, dominated by long strands of
kelp and a variety of invertebrates, as
well as fish such as lumpsuckers,
coley, and wolf-fish.
TEEMING WITH LIFE
Invertebrate life at the bottom of
the channel includes colorful
sponges and anemones.

seabed, including a conical obstruction DISTURBED SEA
ATLANTIC OCEAN NORTHEAST ATLANTIC OCEAN NORTHEAST
known as the Pinnacle, which rises An area of disturbance begins to develop
Corryvreckan to within 95 ft (30 m) of the surface. in the channel north of Jura, seen here with Slough-na-more
The steep east face of this obstruction the island of Scarba lying behind it.
Whirlpool forces a plume of water to the surface, Tidal Race
producing whirlpools and standing
FEATURES FEATURES
Tidal race, standing waves up to 13 ft (4 m) high, and Tidal race with eddies
waves, and whirlpools the roar of the rushing water can and standing waves
be heard up to 3 miles (5 km) away.
TIMING TIMING
Twice daily Over the years, the Corryvreckan Four times daily
has caused numerous emergencies –
the author George Orwell
LOCATION Between the islands of Jura and Scarba, LOCATION Between Rathlin Island and Ballycastle
west coast of Scotland, UK nearly drowned Bay, County Antrim, Northern Ireland, UK
there in 1947.
The most famous tidal phenomenon The Slough-na-more Tidal Race results
in the British Isles can be found in the from strong tidal flows of billions
Gulf of Corryvreckan. Twice a day on of gallons of seawater between the
the flood tide, strong Atlantic currents Atlantic Ocean and the Irish Sea, via
and unusual underwater topography a narrow channel. During spring tides,
conspire to produce an intense tidal the tidal stream can attain a speed of
race. As the tide enters the narrow 8 mph (13 km/h). Where it passes
bottleneck at Corryvreckan, currents Rathlin Island, a complex of fast-
of up to 14 mph (22 km/h) develop. moving currents, eddies, and standing
Underwater, these currents encounter waves is created. In contrast, the same
a variety of irregular features on the sea area is usually calm during other INTRODUCTION
phases of the tidal cycle. In 1915, the
SPIN-OFF VORTEX strength of the Slough-na-more Tidal
In the whirlpool area, massive upthrusts Race forced the Irish steam coaster
of water occur in pulses, producing vortices SS Glentow aground on the Irish
that spin away with the tidal flow. coast, and the ship later broke up.