Triangular interactions among climate, erosion and tectonics happen during the course of formation and development of a mountain range. In this study mountain range of Nyainqentanglha of Himalaya has been focused to assess which element played the vital role in this case. Altitude data of the catchments have been used as the primary key of analysis. Significant concentration of catchment areas near glacier equilibrium line altitudes (ELA) proved the presence of glacial buzzsaw mechanism. Swath analysis confirmed the presence of Teflon peak. Finally web of interrelationship has been explored behind the development of this mountainous range.

1. Topographic Analysis: Linkages among Climate, Erosion and Tectonics
Shahadat Hossain Shakil
ABSTRACT
Triangular interactions among climate, erosion and tectonics happen during the course of formation and
development of a mountain range. In this study mountain range of Nyainqentanglha of Himalaya has been focused
to assess which element played the vital role in this case. Altitude data of the catchments have been used as the
primary key of analysis. Significant concentration of catchment areas near glacier equilibrium line altitudes (ELA)
proved the presence of glacial buzzsaw mechanism. Swath analysis confirmed the presence of Teflon peak. Finally
web of interrelationship has been explored behind the development of this mountainous range.
……
INTRODUCTION
Since Dahlen and Suppe (1988)
explored that „erosion can affect the
tectonics of the region undergoing that
erosion‟, researchers have been drived to
discover the interactions among not only
erosion and tectonics but also climate,
which affects erosion and is affected by
tectonics (Molnar, 2009).
Topography represents the net product
of tectonic and surficial processes.
Interactions between tectonic and
surficial processes are complex and
involve coupling with feedback through
diverse mechanisms (Fig. 1).
Fig.1. Feedback loops within the
dynamic system defined by tectonics,
climate and erosional surface processes.
There are two feedback loops; a direct
path (I) whereby tectonics increases
erosion rates by increasing elevation,
relief and drainage basin areas and an
indirect loop (II), whereby increased
elevation induces increased erosion rates
through changes in climate (Adopted
from Willett et al. 2003, p.33)
Mountains are created and shaped not
only by the movements of the vast
tectonic plates that make up Earth‟s
exterior but also by climate and erosion
(Pinter and Brandon, 2005). In
particular, the interactions between
tectonic,
climatic
and
erosional
processes exert strong control over the
shape and maximum height of
mountains (Brozović et al., 1997) as
well as the amount of time necessary to
build or destroy a mountain range
(Pinter
and
Brandon,
2005).
Paradoxically, the shaping of mountains
seems to depend as much on the
destructive forces of erosion as on the
constructive power of tectonics (Zeitler
et al., 2001).
The geology of the Himalaya (stretch
over 2400 km) is a record of the most
dramatic and visible creations of modern
plate tectonic forces (USGS, 1999). This
immense mountain range was formed by
tectonic forces and sculpted by
weathering
and
erosion.
Topographically, the belt has many
superlatives: the highest rate of uplift
(nearly 10 mm/year at Nanga Parbat),
the highest relief (8848 m at Mt. Everest
Chomolangma), among the highest
erosion rates at 2–12 mm/yr (Burbank et
al., 1996), the source of some of the
greatest rivers and the highest
concentration of glaciers outside of the
polar regions.
Nyainqentanglha
Mountains
of
Himalaya forming the eastern section of
a mountain system in the southern part
of the Tibet Autonomous Region of
south-western China, is a 700-kilometer
(430 mi) long mountain range (Fig. 2). It
has an average latitude of 30°30'N and a
longitude between 90°E and 97°E. The
range is divided into two main parts: the
West and East Nyainqentanglha, with a
division at Tro La pass near Lhari. The
Nyainqentanglha Mountains bound the
northwest side of the Yangbajian graben
and are parallel to it (Pan and Kidd,
1992). The average elevation of the
Nyainqentanglha Mountains is about
6000 m. West Nyainqentanglha includes
the four highest peaks in the range, all
above 7000m. It lies to the southeast of
Namtso Lake. East Nyainqentanglha
located in the prefecture of Nagchu,
Chamdo and Nyingchi marks the water
divide between the Yarlung Tsangpo to
the south and the Nak Chu river to the
north. The area is of special interest for
glacio-climatological research as this
[1]
region is influenced by both the
continental climate of Central Asia and
the Indian Monsoon system, and it is
situated at the transition zone between
temperate and sub-continental glaciers
(Bolch et al., 2010).
Fig. 2. NQTL Range Location, bounded
by Tibetan Plateau-north, Bhutan-south,
Himalayan-West, Namcha Barwa-East
REGIONAL SETTING
Geologic mapping in the eastern
Himalayan syntaxis confirmed the three
regional tectonic elements outlined by
previous geologic workers. The Namche
Barwa and Nyainqentanglha crystalline
complexes lie below and above the
Indus-Yarlung Tsangpo suture (IYS),
respectively, and both were parts of the
northern Indian plate basement rocks.
Uplift and exhumation have been the
most recent dominant tectonic processes
in the late Cenozoic for the High
Himalayan crystalline rocks (Namche
Barwa Group) in the core of the Namche
Barwa antiform (Quanru et al., 2006).
Results of a recent study led by Wang et
al. (2013) showed high variation in
extent of glaciers and lakes with
increased temperature and precipitation
in the past 40 years in this area. These
variations include glacial retreat,
increased water level of inland lakes and
increased number of glacier lakes to
higher altitudes.

2. In contrast According to Kang et al.
(2007), an intensification of atmospheric
circulation and increase of sea-surface
and air temperatures, resulting in
intensified moisture availability and
moisture transport, have been a major
cause for the increase of ice-core
accumulation
over
the
Mt.
Nyainquentanglha region since 1980s.
RATIONALE AND METHODS
The aim of this study is to analyze the
topography
of
Nyainqentanglha
mountain range and to find out the
linkages between erosion, climate and
tectonics, and to determine which played
the dominant role in the development of
mountain range.
DEM; seed point of catchment and a
glacier ELA dataset of the study area has
been collected for analysis. TAS GIS
and MATLAB have been used for the
investigation and illustration purpose.
To determine the catchment size, holes
within the DEM has been filled first to
model the stream flow uninterruptedly.
Then using the FD8Quinn algorithm
Specific Contributing Area (SCA) has
been determined. Visually 79 major
catchments have been identified then
with the help of their grid reference a
Seed Point file has been created which
contains these outlets co-ordinates.
Afterwards, watersheds have been
delineated with TAS and converted to
vector for area calculation.
Min, max and avg. elevation and
average slope from DEM has been
extracted for further evaluation. Swath
analysis in MATLAB has been also
performed to visualise the physical
scenario across the range.
Swath
analysis
simplifies
the
topographic
data
for
better
understanding and observations. This
practice is also termed as data reduction
technique. To extract and analyze data
(i.e. correlation with ELA glacier and
elevation) from the complex data
structures of DEM (i.e. plan view) and
to make insights and decision from it
(i.e. following the glacial buzzsaw
hypothesis?). During this process a
DEM is divided into number of clusters
based on visual and statistical symmetry.
Then considering variation of the field
along or across the range, orientation of
Swath is determined. To cover the
identical area within one frame as well
as considering the length of range, width
of the Swath frame is figured out. Each
swath frame records the maximum,
minimum, and average elevation for
each pixel band.
To cover near about eight identical zone
across the range in terms of catchment
size, and to visualize the difference
between the northern catchments (1-46)
and southern catchments (47-79), swath
width has been fixed at 25 km (Fig. 3;
Fig. 4). Orientation of the swath frame
has been fixed across the range
(perpendicular with the longer axis of
the range) to visualize the difference
between north and south catchments.
During this process each swath frame
recorded the maximum, minimum, and
average elevation for each pixel band
(90m by 25 km) perpendicular to the
25–40 km swath length (Fig. 4). Similar
type of approach has been adopted by
Dortch et al. (2011) to determine the
longitudinal topographic variation of the
central Ladakh Range and Kühni and
Pfiffner (2001) in case of topographic
analyses of Swiss Alps mountain belts
along cross-sections perpendicular to the
main structures of different orogens.
Fig. 3 Catchments shape and location;
ID: 1-46, northern side catchments; ID:
47-79 southern side catchments
Swath Analysis: Glaciers concentrate
within the elevation of 5500 – 6000
meter (Fig. 8; Swath 1 – Swath 6). In
swath 1 and 2 glaciers distributes evenly
within the two regions. But in swath 3-6
glaciers concentrates largely in the
southern region (right hand side of the
Divide). No glaciers have been found in
swath 7-8, comparatively lower altitude
region of both zones (Fig. 8).
RESULTS
Spatial Pattern of Catchment Size: area
of northern catchments (1-46) range
between 1.65 ~ 86.33 sq.km with an
average of 24.55 sq.km. Whereas area of
southern catchment lies between 7.44 ~
250.7 sq.km with an average of 47.81
sq.km (Fig. 5). Southern part of the
range contains an exceptional catchment
area of 250.7 sq.km which increased the
average value of this part, while the
normal average is slightly higher than
the northern part (Fig. 5).
Elevation vs. Catchment Size: In case of
smaller catchments, southern parts have
lower higher elevation than the northern.
But the reverse scenario exists in case of
bigger catchments, higher maximum
elevation for southern zone (Fig. 6). In
both cases southern catchments have
lower minimum elevation than northern,
resulting higher relief in the southern
zone (Fig. 8). In case of increase in
catchment area for both zones after
certain point elevation decreased, with
couple of exceptions for southern zone.
A positive but weak trend can be seen
for maximum (R2 = 0.352) and average
elevation (R2 = 0.297) and catchment
size. Whereas a negative but very weak
correlation can be seen for minimum
elevation (R2 = 0.041).
Average Slope vs. Catchment Size: For
both smaller and larger catchments,
southern zone have higher average slope
than the northern zone. Southern zones
slope range between 24.81 0 ~ 18.140
(degree), with an average of 22.470. In
contrast, northern catchments average
slope lies between 21.95 0 ~ 14.090, with
an average of 18.960.
[2]
Glaciers are closely related with the
maximum and average elevation line in
swath 1-3. But due to the presence of
some exceptional peak in the southern
zone (Fig. 6), glaciers correlate with the
average elevation line in swath 4-6.
DISCUSSION
Concentration of high proportion of
catchment area (Fig. 6) within the range
(5500 – 6000) of glacier equilibrium line
altitudes (ELA) (Fig. 8) suggesting that
operation of a Glacial Buzzsaw
denudation mechanism effective in
reducing surface topography above the
snowline and concentrating it at the
snowline (Brozović et al., 1997; Egholm
et al., 2009).
This result supports the findings of
Brozović et al. (1997), Montgomery et
al., (2001), Mitchell and Montgomery
(2006) and Brocklehurst and Whipple
(2002) that glaciated orogens in the
Himalayas, the Andes, the Cascade
Range, and the Sierra Nevada (USA)
hold a striking coincidence of snowline
altitudes, glacier equilibrium line
altitudes (ELA) and elevations with a
high proportion of surface area.
On
the
other
hand
some
anomalies/exceptions exist in the
southern zone of the range, by the
presence of some exceptional peak (Fig.
8; swath 4-5). This has been has termed
as Teflon Peak by Anderson (2005),
which cannot be well described through
glacial buzzsaw. So the range is better
characterized as a non-uniform scooping
of the landscape between high hard
slippery Teflon peaks (Anderson, 2005).

3. Fig. 4 Swath profile location and orientation; red box – swath frame,
blue points – glacier location
Fig. 5 Spatial pattern of catchment size
Fig. 6 Elevation vs. catchment size; elevation: minimum (circles),
average (squares) and maximum (triangles); marker: filled (northern),
hollow (southern); trend lines: min. elevation – green line, avg.
elevation – yellow line, max elevation – red line; R2 = square of the
correlation coefficient between the regression line and basin data
Fig. 7 Average slope vs. catchment size
Fig. 8 Swath Profile of the Range; lines: blue – max elevation, red –
avg. elevation, green – min elevation; black points – glacier location;
[3]

4. According to Anderson (2005, 2010),
during glacial buzzsaw process glaciers
erode along the slope which make it
more steeper. This proposition can be
supported through the result of Fig. 7,
stating steeper peaks in the southern
zone, where majority of the glaciers
exists (Fig. 8; swath 2-6).
High relief has been experienced from
the swath profile (Fig. 8; swath 1-5) of
the range in the southern zone. This can
be explained by the proposition of
Molnar and England (1990), “glaciations
have been assumed to increase average
relief mainly by incising valley systems,
leaving high elevation peaks and hill
slopes almost unaffected, and producing
significant isostatically driven peak
uplift”.
CONCLUSIONS
Mountains of Nyainqentanglha range
follow the glacial buzzsaw hypothesis.
With some exceptions in the southern
catchments termed as Teflon peak in
geology. Glaciers clusters largely in the
southern zone due to higher altitudes. In
another sense presence of the glaciers
played the crucial role for the
development of this higher altitude
through more erosion therefore uplift
feedback from the inner tectonics.
Influence of local climate is also very
crucial behind the formation and
development of mountains as well as
glaciers, which can be said in reverse
way also (Molnar and England, 1990;
Anders et al., 2010; Dahlen and Suppe,
1988; Egholm et al., 2009; Molnar,
2009; Willett et al., 2003). This study
echoes the complex interrelations of
tectonics, erosion and climate during the
development of a mountain range, which
is driving researchers of modern times in
the domain of geology to unravel the
hidden layers of this relationship.
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ACKNOWLEDGEMENT
Author expresses his gratitude towards
Dr Jason Dortch, Lecturer in Physical
Geography, SEED, University of
Manchester for his continuous guidance
during the course of this study and
specially for the MATLAB script.
Author is also thankful to Emma
Shuttleworth (GTA) for her assistance
during the surgery works.