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formation and precipitation slowly decrease and the
storm cell disappears. Under some circumstances,
the advancing cold front may entrap another lobe of
warm air, generating a secondary low to the south-east
of the original one that is now dissipating. It is even
possible for the rotating air aloft to circle back to the
original site of cyclogenesis, and trigger the formation
of a new low-pressure wave along the polar front.
These extra-tropical lows or depressions, because of
their method of formation, have the potential to
produce the same wind strengths and precipitation
amounts as tropical cyclones. However, because they
are larger and more frequent, they pose a greater
hazard. Such extra-tropical storms also can generate
ocean waves and storm surges similar in magnitude to
those produced by tropical cyclones.
ember 1099, 18 November 1421 and in 1446
also killed 100 000 people each in England and the
Netherlands. By far the worst storm was the All Saints
Day Flood of 1-6 November 1570. An estimated
400 000 people were killed throughout western
Europe. These death tolls rank with those produced in
recent times in Bangladesh (East Pakistan) by storm
surges from tropical cyclones. An English Channel
storm on 26-27 November 1703, with an estimated
central pressure of 950 hPa and wind speeds of
170 km hr -1 , sank virtually all ships in the Channel with
the loss of 8000-10 000 lives (Figure 3.13). Other
storms with similar death tolls occurred in 1634, 1671,
1682, 1686, 1694 and 1717 at the height of the Little
Ice Age. Much of the modern-day coastline of northern
Europe owes its origin to this period of storms. Erosion
in the North Sea was exacerbated by 30 notable,
destructive storm surges between 1000 and 1700 AD.
North Sea storms reduced the island of Heligoland,
50 km into the German Bight, from a length of
60 km around the year 800 to 25 km by 1300 and to
1.5 km by the twentieth century. The Lucia Flood storm
of 14 December 1287 in northern Europe was of
immense proportions. Before that time, a continuous
barrier island bordered the Netherlands coast. The
storm breached this coastal barrier and formed
the Gulf of Zuider Zee (Figure 3.13). It is only recently
that the inlets at these breaches have been artificially
dammed. Smaller embayments further east at Dollart
and Jade Bay were also initiated and the Eider Estuary
was widened to its present funnel shape. The same
storm in northern France eroded several kilometres of
marsh, making one headland a distant offshore island.
In the Great Drowning Disaster storm of 16 January
Historical events
(Wiegel, 1964; Lamb, 1982; Whipple, 1982; Milne,
1986; Bresch et al., 2000)
Mid-latitude depressions have also been as devastating
as tropical cyclones. Their effects are dramatic in two
areas, namely along the eastern seaboard of the United
States and in the North Sea. Historical accounts for
these areas document the strongest storms recorded.
Figure 3.12 plots the number of recorded cyclonic
depressions in northern Europe that have produced
severe flooding over the past 2000 years. The Middle
Ages was an unfortunate period of cataclysmic
tempests that caused great loss of life and immense
erosion. Four storms along the Dutch and German
coasts in the thirteenth century killed at least 100 000
people each. The worst of these is estimated to have
killed 300 000 people. North Sea storms on 11 Nov-
Channel coast
Nort h Sea coast
Incidence of severe North Sea and English Channel storms per century for the last 2000 years (Lamb, ©1982; with permission from
Methuen, London).
Fig. 3.12
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