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| Titel |
Monitoring morphological changes in an arid zone by spaceborne images and aerial photography between 1945 - 2009; the Yamin Plateau, Israel |
| VerfasserIn |
Guy Hetz, Dan Blumberg, Dody Avraham, Hai Cohen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037919
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| Zusammenfassung |
| This research focuses on a geomorphic mapping of the Yamin Plateau in southern Israel
which is part of the Yamin-Rotem Syncline and covers about 200 km2. This area has been
restricted since the 1950s and therefore, provides a unique opportunity to study undisturbed
geomorphic processes. Nowadays, the national nuclear waste depository is located in this
area accepting waste from industrial factories, research institutes and hospitals. This is the
main reason why environmental processes are of major interest in terms of landform changes
in space and time.
The exposed geology section of the Yamin Plateau mostly consists of the Miocene
Hazeva Group where sedimentary processes started 20 million years ago and continued for
12-14 million years. Two formations of the Miocene Hazeva Group appear in the study area
Zefa and Rotem. The compositions of these two formations are similar and sometimes
defined as "the main sand body" in the Hazeva Group. The restriction of the area stopped the
grazing and let the development of a biological soil crust on the surface. The research
objective was to document and characterize landform changes from 1945 until 2009 within
the Yamin Plateau based on spaceborne images and aerial photography. All the parameters
we extracted in the laboratory were validated with field measurements. A combination of the
spaceborne images, aerial photography and field measurements leads us to the following
conclusions:
The research results show that soil stabilization processes took place earlier
than the area closure. Inspite of decreasing precipitation tendencies as measured
during the last 50 years in Yamin Plateau, the vegetation cover increased from
55% in 1945 to 67% in 2009. The main reason for this is the area closure and
reduction in grazing along with developing of vegetation and biological soil
crusts.
Field studies and image processing of aerial photographs and recent QuickBird
images alongside grain-size distribution show that in the past there were active
zibar morphologies in the region. The most frequent grain-size of 350 μm
supports this.
Although the current geology map of the Yamin Plateau is characterized by sand
soil texture, nowadays the study area surface contains 50% of clay minerals,
which were probably trapped by soil crusts during dust storms.
A grain size analysis shows the dominance of medium-coarse sand (350 μm)
that partially mantle the Yamin Plateau surface. Aeolian activity that took place
in the past and was concentrated in the southern and eastern parts of the plateau
and included linear zibars.
We also present a new index, the Clay Crust Index (CCI) that includes the combination of the
Crust Index and the 7-th band of the Landsat TM that covers the clay absorption range. The
idea behind this combination is based on trapping of clays by biological soil crusts which
deepens the absorption feature in the spectrum of 7-th band of the Landsat TM. From 1945
to 2004 there were no evidence that indicate aeolian nor fluvial activities. Yet, a
single extreme rain event that took place in 29 October 2004 caused the largest
landform changes in the past 60 years. The runoff widened in the eastern channel
streams.
To summarize, the study area’s closure in the late 1950’s had contributed to the
decrease of aeolian processes. The fluvial processes are very limited, yet, when there
is an unusually large rainstorm event there is a risk of undermining and extreme
erosion processes, especially when the surface is covered by soil crusts and clay. |
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