ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

aLAVI HEIKKINEN & PETER BRUSILA
Field techniques employed in Finnish dune research
Department of Geography, University of Oulu, FIN-90570 Oulu, Finland
Dune sand movements can be monitored either in the
course of aeolian events or afterwards. Thus research techniques
can be divided into active ones that form part of the
processes or measure their progress and passive ones that
measure the changes brought about as a result of the
processes.
One obvious active technique is the marking of blown
sand with a fluorescent tracer that can be distinguished by
UV illumination in order to monitor the dissemination of
the sand. Saltation can be studied either using traps of a
certain kind or with strips of wood stuck into the ground
and covered with vaseline or some other substance to which
the sand will adhere easily. Other active approaches include
the gathering of meteorological data, including wind
speed and direction, air humidity, precipitation and temperature.
This information, especially that concerned with
winds, can be used to predict the likelihood of aeolian erosion
and total transport of blown sand in a given area.
Passive methods include various traps, erosion gauges, levelling
procedures and the measuring of the sand content
of snow samples. The authors have recently tested a number
of new traps for collecting blown sand, including the
Annika, Alestalo, Erika and BP 1-2 models. Some of these
measure the total amount of sand transported, some that
transported by saltation and some the crawling sand, while
some accept sand from all directions and others only from
a certain direction. These traps are suitable for different
purposes, and each has its good and bad points, but there
is no one trap that is yet capable of providing a proper account
of the spatial distribution of the sand.
The shapes and stratification of dunes provide information
on wind directions at the time of their deposition, and
changes in the morphology and vegetation of dune areas
can often be assessed from historical documents, maps of
different ages and repeated field or remote sensing surveys.
The stratification of a dune, other aspects of its internal
structure and variations in its water content can be determined
by ground penetrating radar, a method in which the
depth dimension and resolution can be varied by using antennae
of different frequencies. Thin buried charcoal
layers, which may provide evidence of earlier fires, can be
identified by drilling if they cannot be distinguished by
ground penetrating radar. These layers can be dated by radiocarbon
and the sand horizons above and below them by
the luminescence methods. Dendrochronological techniques
can be employed in a wide variety of ways for dating
accumulation and deflation events in dune areas. Features
that can be particularly revealing in this sense are barrelshaped
growth, release and suppression in radial growth,
annual ring eccentricities, reaction wood, the age of the
trees and adventitious roots.
JORGEN HERGET
Anthropogenic influence on the development of the
Holocene terraces of the River Lippe (W. Germany)
Geographisches Institut NA 4, Ruhr-University Bochum,
Universitatsstralie 150, D-44801 Bochum, Germany
The Holocene Inselterrasse (Island-terrace) of the river
Lippe lying between the Westphalian bight and the
northern rim of the central german hill country in the
northwestern part of Germany was one of the focus points
during studies on the development of the Lippe-valley
system.
As terrace level the Inselterrasse is only existing between
the city of Limen and the mouth of the Lippe into the Rhine.
It is diverging from the lowest floodplain level west of
Liinen, reaches a higher level of about 3 m and converges
again west of the city of Haltern in the direction of the
Lippe mouth. In the headwaters east of Limen the valley
bottom below the Weichselian Niederterrasse (lower terrace)
consists of a single broad level. West of Liinen the Inselterrasse
builds the valley bottom and only dry abandoned
river channels segregate the level of the Inselterrasse
into several islands. In detail in some sections the Inselterrasse
consists of two levels but due to the recent sediment
dynamics with the accumulation of natural levees they
usually are difficult to differentiate. The lowest level of the
callow is a small sector following the river channel. Several
samples of wood, humic loam and peat out of the terrace
sediments and channel fills were dated by radiocarbon,
pollen analysis and dendrochronology and show ages that
vary between less than 300 years and 8230-8005 B.C. More
detailed sediment studies could not be carried out because
of the lack of exposures but the sandy terrace sediments
seem to be cross-beded and deposited by a meandering
river.
The origin of the level of the Inselterrasse is completely
anthropogenic. Between the 13 th and 19 th century meanders
were cut and the river channel was narrowed for reaching
a higher depth of water. The aim was the improvement of
the navigation of the river. Studies about the Roman activities
on the river channel during their campaign against the
german tribes are in process. The deep erosion of the river
channel makes the mean water level fall deeper below the
natural high-water bed. This relatively risen level is the recent
Inselterrasse. The occurence of this anthropogenic terrace
results from the river management which ended close
to Limen because of cliffs of harder rock there. The lowest
terrace level close to the river channel developed out of the
towing-path. It is extented by fluvial erosion but also covered
by high-water sediments and natural levees. A research
program on the character of the natural river channel of
the Lippe, meandering or anastomosing (resp, a sectional
divarication), is in progress.
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