Other Abstract | There are some distinct characters from other regions on topographic character and interior structure of crust in eastern Tibetan Plateau, so in order to research
processes and mechanisms of the Tibetan Plateau peculiar topography formation, and
the relation between uplift of the plateau with topography formation, and the response
relationship between the surface processes and topography landscape, climate change,
activity tectonic. So we choose Longmenshan region in the southeast edge of the
Tibetan Plateau as research objects, base on the SRTM DEM and GTOPO 30 DEM
data to quantify the topography characters, analyze the hydrological data, and quantify
the surface modern erosion rates in every drainage basins of this area, integrate the
stratum character and the precipitation distribution information, to explore the
response and feedback between surface processes and uplift, climate change under the
special topography of eastern Tibetan plateau, and to conclude that the active tectonics
are strong constrain to the spatial distribution of modern erosion rates in eastern of
Tibet Plateau base on geomorphic characteristics and drainage patterns, that is active
tectonics tectonic uplift ( the difference uplift between two sides of active tectonics)
elevation difference Gravitational potential energy high modern erosion rates.
This thesis draws conclusions as following:
There are similarity characteristics between time series of modern erosion rates
with inter-annual charge, but there are some differences in different climate zones. At
the same time, the seasonal variation of erosion rate is very obvious in all Hydrometric
Stations, the erosion during the rainy season accounted for 85% -97% of the total
erosion, and there are some differences in different climatic zones.
Modern erosion rates from several decades of hydrological station data in
Longmenshan mountain area place important constraints on the surface processes of
special topography at the margin of the eastern Tibetan Plateau. The data show that
modern erosion rates are characterized by great heterogeneity in this drainage basin:
in the interior of the Plateau, modern erosion rates are relatively low (<0.1mm/yr). In
the margin of the Plateau, modern erosion rates are very high (>0.3mm/yr). In the
alluvial plain (Sichuan basin), modern erosion rates are between 0.15 to 0.3mm/yr. we
found that distribution of high modern erosion rates is zonal along Longmenshan
region, and the erosion rate be gradually decreased on both sides of the Longmenshan
Mountains faults. And we can find that there are tremendous similar in spatial
distribution between hydrological calculated method and Cosmogenic Be-10 and Al-26,
but lower than low-temperature thermochronology, it may be owing to the defference of
time scale among these methods, the time scale is short in hydrological calculated
method and Cosmogenic Be-10 and Al-26, it may be neglected the effection of the
large tectonic activity, e.g. large earthquake, but low-temperature thermochronology
calculated the effection of the large tectonic activity, in addation, it may be
overestimate the modern erosion rates because it was extrapolated based on some
single-point measurement results.
Interaction between modern erosion rates, landscape evolution, climate change
and tectonic activity shows that tectonic activity plays an important role in affecting
modern erosion rates; climate change is not the dominant factor; the spatial trend
between the modern erosion rates and the topography characteristics is significantly
similar.
At the same time, we found that coupling relationship among landslide events of
the earthquake, landscape characteristics and tectonic activities was similar to erosion
rate, so we didn’t highlight the special events effect to erosion rate.
In the end, we conclude that the special topography characters are mostly due to
tectonic activity and surface erosion and its flexural isostatic compensation of the
mass removed in the margin of the eastern Tibetan Plateau. It makes the high relief in
margin of Plateau, and high elevation, low relief in interior of Plateau. |
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