Origins of the Waterfalls of the Callasaja River in NC Appalachians
Chris R. Ormsby in collaboration with Sean Gallen
Abstract
The Southern Appalachian Mountains of North Carolina
maintain a relatively high topographic relief despite the fact
that the orogeny has not been active for approximately 200
million years.
North Carolina State University
Background
Mass Wasting Events
The area studied is shown in Fig. 2 outlined with a black line. This area is
part of the Cullasaja River drainage basin. The portion of the Cullasaja
River in which data was collected is just over 18 km in length starting at the
falls directly below Sequoia Lake in Highlands, NC. At 15 locations along
an 18 km stretch a Schmidt hammer (see methods) was used to measure
the rock-mass-strength.
Moreover, this rugged terrain remains in the face of ubiquitous
mass wasting events. There certainly seems to be a
contradiction. Why are these slopes not more glacis?
Methods
Mass Wasting: refers to the process of Earth material being
move downward by the force of gravity. In the Cullasaja River
basins most mass-wasting takes place as debris flows.
In order to disprove the hypothesis that the rock-mass-strength
is greater at the waterfalls we took compressive strength
measurements at each of the 5 knickpoints listed in Fig. 7 as
well as above and below each of the falls.
Fig. 2
In this study we test the hypothesis that knickpoints in the
Southern Appalachians are stalled on resistant rock-types in
the Cullasaja River basin. We collected measurements of
relative rock compressive strength of bedrock river channels
in the Cullasaja River.
Our findings lead us to conclude that variations in rock-type or
rock strength do not control the formation of knickpoints in the
Cullasaja River basin. We instead favor the hypothesis that
the knickpoint in the Cullasaja River basin are mobile and
formed elsewhere by some other mechanism.
Introduction
Typically tectonically inactive mountain ranges do not
maintain aspects distinct in active orogenies such as of high
relief, steep hillslopes, and periodic mass wasting events, yet
the Southern Appalachians are an exception.
One explanation suggests that knickpoints are created where
the rock-type is harder and therefore less susceptible to
weathering, implying that knickpoints are stalled. If this is
true, then some other process(es) must be called upon to
explain the rugged terrain of the Southern Appalachians.
We test the hypothesis that rock compressive strength
controls the development of knickpoints in the Southern
Appalachians by conducting a field investigation in the
Cullasaja River that contains five major knickpoints.
The Appalachian Mountains are shown with a white dashed
line in figure 1.
Fig. 1
Knickpoints
Fluvial network is defined by channels draining areas greater than
0.125 km ². (A) Geologic map of the Cullasaja fluvial network
(NCGS, 1995). (B) Shaded relief map with location of mapped
mass wasting from Wooten et al. (2008).
Results & Discussion
Knickpoints: a steep convex upward reach in an otherwise
convex downward profile. In many instances, they form in
response to base level fall and are frequently interpreted to
represent the mobile boundary
separating the actively adjusting
channel below from the relict
channel above.
We hypothesize that the
Cullasaja River Basin preserves
a relict landscape because the
knickpoints are mobile.
One common explanation suggested that knickpoints are
created where the rock-type less susceptible to weathering.
We set out to show there is no correlation between rockmass-strength and waterfall location. Fig. 8 shows an overlay
of each waterfall, field site, as well as the comparative rockmass-strength. The data clearly shows that, within the
Callasaja River basin lithology, there is no relationship
between the waterfalls location and the bedrock strength.
Fig. 3
An alternative hypothesis is that knickpoints form on rock-types
that are more resistant to
weathering. (Fig. 4) : If more
resistant rock-types are found
To correlate with knickpoints,
Then knickpoints are not
related to mass-wasting and
Relief enhancement in this
region.
Fig. 4
Fig. 7
It is our assertion that these knickpoints are not stalled. In
fact, there is evidence of flutes and potholes throughout the
river, indicating the channel is incising and the waterfalls are,
in fact, mobile.
Methods
Rock-mass-strength measurements were conducted with a
Schmidt Hammer. This device, shown in Fig. 5, is used to
measure the strength of rock. The hammer measures the
rebound of a spring loaded cylinder. The results are indicated
on an arbitrary scale from 0 to 100. These results are then
used in conjunction with a provided chart (fig. 6) to determine
the compression strength of the rock.
Fig. 8
Fig 5
Participants
Fig 6
Research made possible by the National Science Foundation in
collaboration with Wake Tech Community College and North
Caroline State University. Data collection and analysis by Chris
R. Ormsby and Sean Gallen both of North Carolina State
University.