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Well developed terraces along the course of the Tahan Creek
can be excellent geomorphic features to reveal
neotectonic activity of northern Taiwan. In earlier
Japaness occupation stage, many researchers have
studied these terraces. However, neither detail study about the
gravel deposits of terraces, nor correlation between
knickpoints of longitudinal profile and geomorphic surface
of terraces has been made yet. This study
collected a lot of good quality topography maps and aerial
photographs. We use these data and a 40 40 grid Digital Terrain
Model (DTM) to make quantitative geomorphologic analysis
of terraces and longitudinal profiles of stream by
the assistance of a Geographic Information System
(GIS), called "MapInfo". We applied field investigation,
measurement of gravel deposits and morphological dating
technology to study the correlation of terraces. Then we can
clarify the landform evolution of the Tahan Creek as well as
the time and spatial distribution of
paleogeomorphic surface during a river capture event.
The result shows that the so-called LTI and FTI terraces are
correlatable in relative-elevation and their covering gravel
deposits. They widely distributed in the region, at mid-
section and downstream of the Tahan Creek. These two
important geomorphic surfaces were formed just before and
soon after the paleo-Tahan Creek was captured. They
could be correlated to two main knickpoints of riverbed nearby
Yeheng and Rong-hau in the upper most mid-section of the
Tahan Creek. Their elevations are 520 and 350 meters,
respectively. We try to use
morphological dating method to date the age of the
terraces in the study area. But we found that the thickness of
the gravel deposits of them is too thin and it is difficult
to analyze with a linear diffusion model. Terraces of the
Tachi group, however, are datable. A terrace called
"Tawanpin" in the Chiaopanshan terrace group is also
datable, because it is covered by thicker deposits. The Tawanpin
terrace(LTI) is dated to be about thirty-one thousand years and
this age is similar to those lateritic terraces(LTI) at
Tachi and Taoyuan area. We suggest that to establish three
dimension terrace degradation model, and to discuss the
form of transport equation may be important in further
study. We wish to solve the morphological dating problem of
terraces that is covered by thinner gravel deposits.
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