Analyses of Streamlined Till Deposits

Drumlin measurement comparisons

Drumlin Orientation

Asymmetry

Understanding controls on Connecticut drumlin morphology, location, and orientation using LiDAR and GIS analyses Ken BOLING and Michael WIZEVICH

Central Connecticut State University bolingkes@ccsu.edu

Understanding controls on Connecticut drumlin morphology, location, and orientation using LiDAR and GIS analyses Ken BOLING and Michael WIZEVICH

Central Connecticut State University bolingkes@ccsu.edu

Conclusions

References

• Drumlin orientations appear be locally affected by topography (local relief)

while following a general regional trend. The regional trends of drumlin axis

directions appear to be controlled on a scale larger, possibly on the glacial lobe

scale.

• Till deposits tend to occur on the up-flow and down-flow sides of

obstructions in areas of high relief.

• In areas of high relief, drumlin asymmetry is controlled by the local

topographic morphology.

• In areas of high relief, drumlin size is controlled by the inter-hilltop space.

• LiDAR is a useful tool for delineating the morphology of drumlins and other

glacial features.

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Introduction

The surficial material in Connecticut was deposited primarily during

the Quaternary glaciations. Much of this material occurs as till deposits, some of

which have been streamlined to form drumlins. The analysis of these landforms

may reveal important information about the paleoglacial conditions which

produced them. These landforms were mapped by the USGS in 2001 using air

photo based contour maps. Recently, a set of high resolution digital elevation

models (DEM) produced from the Connecticut LiDAR (Light Detection And

Ranging, an optical remote sensing technology) data collected in 2000 was

released. However, a state-wide analysis of these features using this data has not

been done.

This study integrated the LiDAR DEMs with 10 ft. horizontal

resolution and 1 ft. vertical resolution obtained from the CLEAR website

(http://clear.uconn.edu.) Over 1600 streamlined features were mapped over the

state of Connecticut, an area of 14,356 km2. Streamlined till features were then

separated into categories based on their morphology and relation to bedrock

obstacles. The morphologic type, morphometry, orientation, and location of these

forms were analyzed and compared to the original Quaternary map produced by

the USGS and bedrock geologic map of Connecticut.

Examining the map of drumlin long-axis orientations (Fig. 4a), several flow patterns become apparent. The

orientations of the drumlins in the western and eastern highlands are generally northwest to southeast, however in the

central Hartford basin the drumlin orientations are northeast to southwest. This is also seen when comparing drumlin

elevations with axis direction (Fig. 4b).

It is commonly stated that the shape of a drumlin is an indicator of flow

direction, such that they have a longer down-flow side and a shorter up-flow side. This is

apparently not true for the Connecticut drumlins. Drumlins in Connecticut are equally

disposed to be oriented with the steeper side in the up-flow or the down-flow direction. The

reason for this variation in asymmetry appears to be due to differences in the elevation of

each side. Drumlins occurring on the up-flow side of an obstruction tend to have a shorter

down-flow side than drumlins on the down-flow side of obstructions (Fig. 6).

Stone, J.R., Schafer, J.P., London, E.H., DiGiaronno, M.L., Lewis, R., and Thompson, W.B.,

2000, Quaternary map of Connecticut and Long island sound basin: U.S. Geological Survey,

scale 1:125000 sheet 1 of 2.

Clark, C.D.; Hughes, Anna L.C.; Greenwood, Sarah L.; Spagnolo, Matteo; Ng, Felix S.L.. 2009

Size and shape characteristics of drumlins, derived from a large sample, and associated scaling

laws. Quaternary Science Reviews, 28 (7-8). 677-692.

Figure 3a. Drumlin field in northwest Connecticut. These drumlins

sit at a high elevation on top of high-relief, hard metamorphic

bedrock. Till is easily differentiated from bedrock; till deposits

appear smoother and lack jointing or structural patterns.

Classifications of Drumlin Morphology

Full LiDAR map of Connecticut, Colorized for elevation, compiled from

115 quadrangle maps downloaded from the CLEAR site.

h

Methodology Each streamlined till feature identified in the survey was manually

digitized using ArcGIS software. Two line features representing the long axis and

width measurements, as well as a point feature at the highest elevation along the axis

were created for each drumlin. The width and highest point were determined using a

5-ft contour map generated from the LiDAR DEM. The long axis was determined

using an “aspect” map, which assigns each slope direction in the DEM a different

color, making the central axis readily apparent (Fig. 1). The actual spatial values for

these data points were then interpolated directly from these created features, using

the LiDAR DEMs as a base to calculate elevation. The advantage to this approach is

that the DEM contains detailed elevation data which can be determined for any

point.

Figure 1. Drumlin axes can easily be determined using an aspect map to

show the point where the direction of the slope is reversed.

Classic Drumlin-

Streamlined till deposit that

forms a topographic high

point relative to the

surrounding area. It has a

relatively smooth and

regular surface. It has a base

that is clearly

distinguishable from

surrounding drumlins and

does not appear to be

associated with bed rock. Figure 2a. classic drumlin with high

symmetry on the western side of the

central valley.

Down-Flow Obstruction

Till Accumulation-

Streamlined till deposits that

occur on the down-flow side

of a bedrock obstruction to

flow.

Figure 2c. Feature occurring on the

down-flow side of a basalt ridge that

obstructed flow.

Figure 2b. Several drumlins on top of a

large till deposit on the eastern side of

the valley.

Complex Drumlins-

Drumlins that occur together

in large complexes, and

have bases which are

indistinguishable from one

another.

Irregular streamlined

deposits – Streamlined till

deposits which are similar in

appearance to drumlins but

do not fit into the other

categories due to their

apparent association with

underlying bedrock, possibly

due to their thickness.

Figure 2e. Highly irregular streamlined

deposits, occurring in an area of high

relief, shown in aspect.

Up-flow obstruction till

accumulation- streamlined

till deposits which occur on

the up-flow side of an a

bedrock obstruction to flow.

Figure 2d. Streamlined till deposits

occurring on the up-flow side of an

obstruction, shown here on an aspect map.

Due to the variety and complexity of the streamlined till

deposits mapped in this survey, it was necessary to organize

them into categories:

•Complex Drumlins

•Classic Drumlins

•Down-Flow Obstruction Till Accumulations

•Up-Flow Obstruction Till Accumulations

•Irregular

After mapping and categorizing these features, several regional trends became apparent. The drumlins in the

northern part of the basin are mostly classic drumlins, except for the complexes on the eastern edge of the basin (Fig. 3d)

While in the southern areas of the basin, drumlins tend to form small complexes on the up-flow sides of the basalt ridges, but

are absent on the down-flow sides. The most densely populated drumlin fields occur in the metamorphic highlands(Fig. 3a and

3b). Both of these fields occur on the down-flow side of regional-scale metamorphic ridges. Obstructions seem to control the

locations of till accumulation (Fig. 3c).

Figure 3b. Drumlin field in northeast Connecticut. Drumlins occur

on top of bedrock ridges that appear to be controlled by structural

trends. They mainly occur together with indistinguishable bases

(drumlin complexes).

Figure 3c. Drumlins on top of thick till deposits that accumulated

on both the up-flow and down-flow sides of a ridge-forming

granitic gneiss.

Figure 3d. Classic drumlins in the Mesozoic Hartford rift basin

sit on the low relief, relatively soft sedimentary rock. These

drumlins are very regular, but some have been modified by

processes when surrounded by glacial Lake Hitchcock. The

complexes of drumlins on the eastern edge of the basin sit at a

higher elevation.

Several morphometric variables were determined for each drumlin, including length, width, elongation ratio

(length/width), up and down-flow axis angles, underlying rock type, axis direction, elevations at the highest point and end

points of the drumlin axis, and asymmetry ratio (up-flow distance / down-flow distance). These values were then analyzed

to determine any relationships.

The most frequently referenced drumlin attribute is the length / width ratio, which is believed to indicate ice-

flow velocity. For this study the length / width ratio did not appear to have any spatial pattern, however plotting the length

against the width yields a graph very similar to those produced in a different study (Clark , 2009).

0.00

200.00

400.00

600.00

800.00

1000.00

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1400.00

1600.00

200 220 240 260 280 300 320 340 360

Ele

vati

on

(ft

)

Direction (Polar degrees)

elevation vs direction

Stand-Alone

Complex

Down-Flow Obstruction

Up-flow

Obstruction

Rock-Associated

0.01

0.10

1.00

10.00

0.00 0.50 1.00 1.50 2.00

Asy

me

try

rati

o (

log)

Front / back elevation ratio

Asymetry vs elevation ratio

Stand-Alone

complex

Down-Flow Obstruction

Up-Flow Obstruction

Irregular

0.0

1000.0

2000.0

3000.0

4000.0

5000.0

6000.0

7000.0

8000.0

9000.0

10000.0

0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0

Len

gth

Width

Length vs Width

Stand-Alone

Complex

Down-Flow Obstruction

Up-flow Obstruction

Rock-Associated

Figure 4a. Long-axis azimuth orientations colorized ranging from

green (120o) to red (210o)

Figure 4b. Drumlin elevation plotted

against axis direction. The smaller

grouping at the bottom is the area of the

central basin where the axis direction

changes.

Classic Drumlin

Complex Drumlin

Irregular

Up-flow

Down-flow

Figure 5. drumlin

axis length plotted

against width

Figure 6. Drumlin front/back elevation ratio plotted against asymmetry ratio.

Note that the up-flow and down-flow drumlins are different.