Environmental Engineering Reference
In-Depth Information
MEDIEVAL STORMS AND COASTAL DUNES
human impact
The Medieval Warm Epoch and the Little Ice Age which followed it represent the
principal climatic oscillation of the last millennium (see Chapter 9) and the switch from
one to the other was marked by climatic instability and more extreme weather events.
Then, as now, the long British coastline was vulnerable to rapid change through the
coincidence of meteorological, eustatic and geomorphic shifts. Marine transgression,
however minor, is likely to have pushed sediment shoreward and abandoned it during the
subsequent regression. Some material was recovered in storm surges reaching beyond the
range of transgression. There are many cases of ports and farmland lost to storms,
particularly on the European North Sea coast. Elsewhere, onshore gales mobilized large
volumes of dry sand in the backshore (see Chapter 17) and formed coastal dunes.
Many events of rapid dune development and the
ensanding
of settlements occurred on
the coast of Wales during later medieval times. Approximate ages and rates of formation
are known from radiocarbon dating, the dates of buildings and historical records. Dune
slack peats yield
14
C dates showing rapid northward growth of a small dune system at
Ynys Las in the mid-fifteenth century. The dunes surmount an older shingle ridge which
bars the Dyfi estuary at Borth. Llangennith Burrows, a 3 km
2
dune 'wedge' enclosing the
northern end of Rhossili Bay in Gower, finally ensanded a Norman church there after AD
1200. In Gower smaller dunes also bar Oxwich and, at Three Cliff Bay, they ensanded
Pennard castle, church and vicarage 50 m above sea level by AD 1525. Dunes raised in a
single storm on 6 December 1330 blocked the harbour and estuary at Aberffraw, on
Anglesey, and ensanded valuable arable land.
Aberffraw was the ancestral court of the kings of Gwynedd and Princes of Wales. The
mark of their eventual conqueror, Edward I, helps us to date the impressive dune systems
of northern Cardigan Bay. Two large
morfa
or coastal marshes, each some 25 km
2
, flank
the coast for 20 km between the Mawddach estuary and Vale of Ffestiniog (see Figure
17.11). Their seaward edge is barred by shingle ridges capped with large dunes. Edward
I's military strategy depended on a ring of seventeen castles isolating the granaries of
Anglesey from the natural Welsh fortress of Snowdonia and - crucially - therefore
stocked and garrisoned by sea. Harlech castle, built from AD 1283 with a water gate and
small harbour like many others, was cut off from the sea by AD 1385 through dune
formation 1 km seaward of the original rock shore (Plate 1). Dune formation and other
coastal impacts of this stormy advent of the Little Ice Age changed the configuration and
dynamics of substantial coastal stretches of Britain and Europe. Modern tourism already
threatens dune systems and their protected hinterland through trampling and blow-out
along beach access routes, which rising sea level may now exploit.
