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FIG 305. Movement patterns during the migration of ripples. Movement at three levels in
the water (blue) becomes increasingly marked by eddies as the floor of sand (yellow) is
approached. On the surface of the sandy bed, sand is carried up the upstream side of
the ripples and deposited on the downstream side, building downstream-dipping layers
in the sand. As these movements continue, the ripples will migrate downstream, and this
may be a steady movement if the water continues to flow in a steady way.
The name pingo has been borrowed from northern native ('Eskimo') languages
and applied to hillocks typical of some Arctic areas, formed when lenses of ice grow
within the soil. These lenses may grow until the ice core breaks through to the surface,
forming a hollow like the crater of a volcano which may contain water during the sum-
mer. At Thompson Common ( c7 ), on the A1075 between Thetford and East Dereham,
a Pingo Trail has been arranged, where visitors can see irregular hillocks and hollows
with ponds, believed to have been formed in this way during Devensian cold episodes.
These features, also seen at East Walton ( c9 ; Fig. 307), are further examples of the ef-
fects of soil movements generated by ice growth and melting.
Over the southwestern part of this Landscape the surface blanket contains light
sandy soils, in contrast to the heavy clay soils on the thicker ice-laid material further
east. The name Breckland is used for this area of light soils, which tend to dry out
quickly and lack the nutrients needed to produce good crops. The area has never been
valued for farming and has, even in recent historical times, resembled an arid desert,
subject to widespread dust storms and removal of soil and seeds by the wind.
FIG 306. Patterned ground, 2 km northwest of Oxburgh Hall (Fig. 294, c6 ), very like the
present-day Arctic pattern shown in Figure 17. (Copyright Norfolk Museums and Archae-
ology Service & Derek A. Edwards)
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