glacial group paper

STUDENT PAPERS: GLACIERS, GEO-MORPHOLOGY, AND SEDIMENTOLOGY

Morphological Interpretations of Glacial Formsby Spatial Analysis in the Area Surrounding

Lake Simcoe, Ontario

Victoria R. Balkwill Tweedie, Alicja N. Jazwiec, Taylor P. Johnson, and Isabella E. VitaleSchool of Geography and Earth Sciences / McMaster University / Hamilton / ON / Canada

ABSTRACT

Drumlins are sedimentary geological features that indicate the final direction of glacier movement; as a result, theyare of great interest in understanding past glacial events. In southern Ontario alone, thousands of drumlins have beenmapped and interpreted remotely through the use of aerial imagery or topographic maps. These are often paired withdigital elevation models (DEMs) and/or contour maps offering detailed information about the area of study. This paperpresents the results of a change-detection study that used maps of different vintages of the drumlin-rich area aroundLake Simcoe in southern Ontario. Two topographic maps and two DEMs, each with contours at 25-ft (7.6-m) and 10-mintervals, were compared in three regions: (A) the urban region in the city of Orillia, overlying sand plains; (B) the areaeast of Orillia, on top of clay plains; and (C) the region south-east of Lake Simcoe, overlying till plains. The 7.6-m contourtopographic maps and DEMs display comparable levels of detail; however, over time the drumlins appear to erode, likely aproduct of the underlying sediment in combination with urbanization. The 10-m contour topographic maps display lessdetail than DEMs of the same resolution, suggesting that the popular topographic maps are not the most reliable methodof mapping drumlins.

Keywords: Simcoe County, Lake Simcoe, drumlin, topographic mapping, digital elevation model (DEM), contour mapping

RESUME

Les drumlins sont des caracteristiques geologiques sedimentaires indiquant l’orientation finale du mouvement d’unglacier; par consequent, ils presentent un grand interet pour comprendre les evenements glaciaires du passe. Dans leSud de l’Ontario seulement, des milliers de drumlins ont ete cartographies et tele-interpretes a l’aide de l’imagerieaerienne ou de cartes topographiques. Ces instruments sont souvent jumeles a des modeles altimetriques numeriques(MAN) ou a des cartes en courbes de niveau offrant des renseignements detailles sur la zone d’etude. L’auteur presenteles resultats d’une etude de detection du changement faisant appel a des cartes de diverses epoques de la zone richeen drumlins autour du lac Simcoe dans le Sud de l’Ontario. Deux cartes topographiques et deux MAN, chacun avec descourbes de niveau a 25 pi (7,6 m) et des intervalles de 10 metres ont ete comparees dans trois regions : A) region urbainedans la ville d’Orillia, surplombant des deltas d’eskers; B) la zone a l’est d’Orillia, surplombant des plaines argileuses et C)la region au sud-est du lac Simcoe, surplombant des plaines de till. Les cartes topographiques a courbes de niveau de25 pi (7,8 m) et les MAN affichent des niveaux de detail comparables; toutefois, au fil du temps, les drumlins semblents’eroder, probablement en raison des sediments sous-jacents, combines a l’urbanisation. Les cartes topographiques acourbes de niveau de 10 m comportent moins de details que les MAN offrant la meme definition, ce qui laisse penserque les cartes topographiques populaires ne sont pas la methode la plus fiable pour cartographier les drumlins.

Mots cles : Comte de Simcoe, lac Simcoe, drumlin, cartographie topographique, modele altimetrique numerique (MAN), cartes encourbes de niveau

Introduction

The direction of glacier movement is indicated in the

geo-morphological record of drumlins. These features are

elongated hills composed mainly of glacial deposits, such

as tills, which are formed by processes of glacial ice sheet

movement (Benn and Evans 2010). Pre-existing sediments,

location, and formation-deposition processes determine

drumlin size, shape, composition, and structures (Stokes,

Spagnolo, and Clark 2011). Drumlins most often consist

Cartographica 50:3, 2015, pp. 165–171 6 University of Toronto Press doi:10.3138/carto.50.3.3197B 165

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of varying quantities of medium-grained till with sand

and clay. Southern Ontario alone has between 6000 and

7000 drumlins that have been mapped (Chapman and

Putnam 1966; Stokes, Spagnolo, and Clark 2011). Aerial

photography and topographic mapping are used in the

interpretation and analysis of drumlin features; however,

the technological and mapping techniques used by re-

searchers can influence the conclusions drawn from spa-

tial analysis of the drumlin fields (Hillier and others

2014). Little attention has been paid to how the digital

tools used by scientists to identify drumlins can skew

understanding of these glacial features. This study aims

to examine how the use of different topographic maps

and digital elevation models (DEMs) changes the users’

interpretation of drumlins in regions surrounding Lake

Simcoe, Ontario, and how changes in interpretation over

time may be explained by urbanization and sediment

type.

Study Area

The region of Lake Simcoe, Ontario, is of great interest in

this study as it has an abundance of drumlins identifiable

in digital imagery, diverse rural and urban areas, and dif-

ferent sediments that underlie these glacial features. Three

regions in the area surrounding Lake Simcoe, Ontario,

were analysed in this study, specifically (A) the urban

region of Orillia, overlying sand plains; (B) the area east

of Orillia, on top of clay plains; and (C) the region

south-east of Lake Simcoe, overlying till plains (Figure 1).

These regions are selected as they allow comparison be-

tween an urban area (A) and rural areas (B, C), and each

is located on top of a different sediment type, enabling

morphological changes to be compared based on these

two site characteristics.

Lake Simcoe is surrounded by till plains that are com-

posed of sand, silt, and clay from the glacial Lake Algon-

quin (Barnett 1990). On the till surface south and east of

the lake (region C) the drumlins are oriented in the direc-

tion of glacial advance and are sediment covered (Barnett

1990). In the southern and eastern portions of the water-

shed, north of the Oak Ridges Moraine, the drumlins

form a larger feature known as the Peterborough Drumlin

Field. Fairly shallow till and elongated drumlins were

identified east of Orillia (region B; Chapman and Putnam

1966). West of Lake Simcoe glaciolacustrine sediments are

less predominant, drumlin features are present but rare,

and the till structure differs from other parts of the water-

shed (Barnett 1990).

Figure 1. Map displaying regions of interest for studying drumlins, indicated by stars: (A) urban region in the city ofOrillia, (B) area east of Orillia on top of clay plains, and (C) region south-west of Lake Simcoe (Map data from GoogleMaps 6 2014). For colour version see http://dx.doi.org/10.3138/CART.3197B.

Victoria R. Balkwill Tweedie et al.

166 Cartographica 50:3, 2015, pp. 165–171 6 University of Toronto Press doi:10.3138/carto.50.3.3197B


The Use of Digital Maps for the Identificationof Drumlins

It is important to understand that despite the introduc-

tion of new technology, aerial photography, topographic

maps, DEMs, and contour maps have remained promi-

nent methods for the interpretation of glacial features, as

they offer high-precision information. Spatial analysis of

drumlins often uses aerial photography and topographic

mapping, as demonstrated by several studies. Cook and

Regis (2005) use DEM data to understand shape charac-

teristics of drumlins in the Menominee Drumlin Field,

concluding that elongated drumlins form in areas where

overburden is thinner. For a portion of the Peterborough

Drumlin Field Maclachlan and Eyles (2013) apply existing

topographic digital data for the purpose of identifying and

extracting morphological characteristics. These methods

of study aided in identifying that elongate, asymmetric

drumlins are located in coincidence with a broad bedrock

low (Maclachlan and Eyles 2013). The broad scale of

information provided by aerial photography and topo-

graphic maps is necessary to create an out-of-field view

of drumlin fields to map their proximity, size, and shape.

The use of these digital maps coupled with geographic

information systems (GIS) allows analysis to occur on

shorter time scales, and often with higher precision than

obtaining field measurements (Hillier and others 2014).

Hatterstrand and others (2004) aim to disprove that drum-

lins in central and northern Sweden were formed during

the last deglaciation or any other ice flow event. To mea-

sure formation processes and the evolution of drumlins in

Sweden, a 1:150,000 black-and-white aerial photograph

overlaid with a contour map was used to determine

drumlin morphology and map channels indicative of de-

glacial ice surface slope (Hatterstrand and others 2004).

This information allowed for the measurement of the

length, width, and height of drumlins in the field, to

estimate the approximate time drumlins were deposited

in the area (Hatterstrand and others 2004).

DEMs integrated with aerial photography can be used

to map glacial landforms such as drumlins. A study of

southern Finnish Lapland used this approach to survey

landforms including moraine types, eskers, and those

indicative of glacial flow direction such as drumlins (Sarala

2005). The use of aerial imagery and topographic maps is

predominant in studies that identify the patterning, clus-

tering, and shapes of drumlins within a study area. Using

these together with contour maps, Rowland (1955) found

the area of northern New York to have drumlins that have

spatial variation in shape.

Limitations exist in using these methods to interpret and

map drumlins. Satellite technology remains limited as it

cannot capture what is hidden from view. For this reason

in particular the reconnection to fieldwork is important.

In areas of heavy canopy, for instance, aerial photography

is unable to survey the underlying landform structures

(Hatterstrand and others 2004). The use of DEMs in

research is increasing, which would also facilitate a shift

away from the use of aerial photography coupled with

contour mapping.

Impact of Urbanization on Drumlin Disruption

Simcoe County contains drumlin fields, and it is im-

portant to understand how alteration of these fields may

affect city planning and vice versa. Increased urbanization

in Simcoe County is the result of numerous factors such

as population growth in the Greater Toronto Area, new

business opportunities, and expanding infrastructure.

Surges in Toronto’s workforce and population have re-

quired adjustments in transportation and expansion of

highways toward the Simcoe County area (Birnbaum,

Nicolet, and Taylor 2004, 41). Considerable growth is

occurring in southern Ontario, and, as a result, the devel-

opment of urban areas surrounding Toronto is of extreme

importance. In 2002, 48.7% of the 229,091 immigrants to

the country settled within the Greater Toronto Area (41).

High immigration leading to intra-provincial migration

creates pressure for urban development and change.

Several large-scale developments are being proposed and

discussed in light of this new population influx, including

the Ontario Potato Distributor Inc. (26). In light of new

economic opportunities for Simcoe County, it is impor-

tant to consider the area’s topography in the development

process. Drumlin composition often involves compact tills

which have low permeability and are seasonally saturated

Vegetation removal from urbanized drumlin fields may

therefore induce slope failure and high runoff discharges

(Woodcock, Rogan, and Blanchard 2012). Albeit minor,

this may be worth consideration when planning, as it

would be suitable to implement low-density housing and

preserve the vegetation. Commonly, as seen in Toronto,

new housing developments take the form of high-rise

and high-density neighbourhoods. Drumlins are composed

predominantly of till (Stokes, Spagnolo, and Clark 2011),

which, if disturbed, may lead to material movement. Fur-

thermore, compact till further exacerbates problems as it

has a tendency to be affected by wet-season flooding and

dry-season droughts (Woodcock, Rogan, and Blanchard

2012).

Underlying Sediments

Little research exists comparing the relative changes to

these plains over time. Factors such as relative erosion

rates may influence the interpretation of drumlins in these

areas over time. Sand plains, as found in region A, are

often made up of stratified gravelly sand, likely deposited

in standing bodies of water (Davis 1890). The Caradoc

sand plain near Strathroy and Mount Brydges is a large

Morphological Interpretations of Glacial Forms by Spatial Analysis in the Area Surrounding Lake Simcoe, Ontario



sand-gravel deltaic deposit. These plains are covered with

sand or other light-textured watershed deposits. When

standing water retreated, gravelly alluvium was spread

over the lower parts of the basin (Chapman and Putnam

1966, 236). Clay plains, found in region B, represent clays

and silts that were deposited in deep offshore water. The

Ekfrid clay plain, west and south of the Caradoc sand

plain, is a featureless, flat area that serves as a good aqui-

tard. Till plains, such as those found in region C, are areas

where the surface soil type is glacial till, very dense collec-

tions of clay, silt, and pebbles deposited by a glacier (Dillon

Consulting Limited 2004). Extensive areas of glacial till

form when an ice sheet detaches from the main body

as the glacier melts. Glacial features such as ground

moraines are formed when tills melt out of the glacier,

forming hills (Chapman and Putnam 1966).

Methods

data

Digital topographic maps of the Simcoe County region

were used in combination with a DEM to identify glacial

features. Topographic maps for the years 1945 and 1989

for regions A and B, and for 1939 and 1976 for region C,

were used to identify drumlins. The contour interval of

the earlier topographic maps is 25 ft (7.6 m), while the

later topographic maps have 10-m contour intervals. A

2006 DEM, originally interpolated by the Ontario Ministry

of Natural Resources from contour lines, digital terrain

models, spot heights, water poly segment, and water vir-

tual flow, was converted to contour intervals of 10 m and

7.6 m in ArcGIS 10.2.1 (ESRI Inc.)for comparison with

the topographic maps and one another.

glacial features of interest

Drumlins of different shapes and sizes were identified

visually using contour intervals by their change in elevation

and elliptical shape. The topographic maps and DEMs were

then visually compared to observe differences between the

four digital cartographic representations of drumlins in

region A, B, and C over time.

Results and Discussion

Upon comparing the level of detail in the 1939 and 1945

7.6-m topographic maps to the 1976 and 1989 10-m

topographic maps it was found that features are less pro-

nounced in the 10-m maps. The 7.6-m maps have a lower

contour interval and therefore are able to capture a higher

level of detail in the surface. Topographic maps and

DEMs of the same contour interval in some situations dis-

played surprisingly different information about a region.

Comparing both topographic maps in all three regions

suggests that the later maps (from 1976 and 1989) have

more eroded drumlins, as indicated by fewer contour

lines. Although this may be in part due to the lower con-

tour interval of the 10-m topographic maps, the 10-m

DEM shows more detail, at a level comparable to the

7.6-m DEM map. This suggests that a great amount of

detail is lacking in 10-m-contour topographic maps. The

topographic maps and DEMs of regions A, B, and C are

presented in Figure 2.

Region A displays the eastern side of the urban city of

Orillia, which lies to the north-east of Lake Simcoe. Sev-

eral smaller drumlins can be found in this region around

the shore. The drumlins in the topographic maps are far

more elliptical than in the DEM-derived contours, but

they are still identifiable. It appears that the shape of the

drumlin has changed with time, likely largely as a result

of urbanization in Orillia, and possibly because of the

underlying sediments. The Simcoe region includes a wide

variety of populations, such as summer cottagers and

permanent residents. The population of Orillia, in Simcoe

County, has been steadily increasing since 1961, as seen in

Figure 3. Further increases in population are forecast,

with the population projected to reach 42,344 by 2031.

Often, to allow for construction plots, land is smoothed

out so that buildings can be built on level surfaces. Flat-

tening of land in urban regions can influence the spatial

distribution and interpretation of drumlins. It is also

possible, to a smaller degree, that the sand plains that

underlie the region might contribute to the erosion of

these drumlin features.

Region B is a rural area to the east of Orillia. It has various

drumlins oriented north-east on clay plain sediment.

Figure 2b highlights two drumlins whose shape differs in

the DEM-derived contours compared to in the topographic

maps. The DEMs make the top of the drumlins appear to

be less smooth, with two to three individual peaks that

may have been formed by erosion over time. Interestingly,

the drumlin seems to erode irregularly at its top, altering

its aerial representation.

Region C is a rural region lying south-west of Lake Simcoe

on till plains. Drumlins in this region are more difficult to

identify as they do not appear to be quite as elliptical as in

regions A and B. Larger drumlins in this region do not

appear to vary much with time, while smaller drumlins

disappear as the contour interval becomes larger.

In all cases, general properties such as orientation remain

the same, and while the degree to which drumlins appear

altered varies, it is safe to say that for all sediment types

that were investigated, the drumlin dimensions have ob-

servable differences. These findings are particularly inter-

esting as a variety of studies measure the dimensions of

drumlins to interpret information about characteristics

related to sediment output or flow quantities and past

glaciations.




Conclusion

The study demonstrates that there are several different

approaches to interpreting the elevation of a region re-

motely. The method chosen can alter the perception of

the morphology of glacial features such as drumlins. It

was found that despite their popularity, topographic

maps topographic maps, especially those with 10-m con-

tour intervals, lack important details, even relative to

DEMs with 10-m contour intervals. Variations in drumlin

shape were observed between the topographic maps and

the DEMs, suggesting that the shape of these features has

changed over time, possibly as a result of urbanization

and the sediment type in these regions. However, it is

challenging to qualitatively compare the influence of sedi-

ment type on drumlin interpretation using contour inter-

Figure 2. Comparison of drumlin shapes and elevations using topographic maps and DEMs in regions A, B, and C fromtop to bottom (adapted from National Topographic Series, Canada Centre for Mapping 1939, 1945, 1976, 1989; OntarioMinistry of Natural Resources 2006).For colour version see http://dx.doi.org/10.3138/CART.3197B.




vals. Future studies should focus on quantifying the ero-

sion of these features to assess the relative impact of each

sediment type and urbanization.

Acknowledgements

We thank Dr John Maclachlan for his support and guidance

throughout this research. We also thank the McMaster Uni-

versity Library for enabling us to access a variety of spatial

data, in addition to Vivek Jadon for helping us obtain

population data.

References

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Figure 3. Total population change from 1976 to 2011 in Orillia based on census data (data retrieved from CanadianCensus Analyser 2011).




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