North American Glaciotectonic Maps
A data base of geographic and glaciotectonic features for North
America has been constructed using the ARC/INFO system at the
University of Regina. The geographic base consists of multiple
coverages that include basic geography, continental geology, and
glaciation limits. Glaciotectonic features are classified in
four main categories: basement faults, concealed structures,
ice-shoved hills, and source basins. Two maps have been
published from the data base: Great Plains Glaciotectonics (Aber
et al. 1991) and Glaciotectonic Map of North America (Aber et al.
1995)--jump to references. Original
digital data are located at the Data Access and Support Center (DASC) at the
Kansas Geospatial Community Commons. For more details, see digital data.
Anonymous download at DASC.
The continent-wide distribution of glaciotectonic features
follows the three-zone model for glacial landscapes; distribution
of glaciotectonic features over the continent is related in
general to the presence of deformable substrata. Glaciotectonic
features are particularly abundant in the northern Great Plains
region, where ice sheets advanced upslope over soft substratum.
Basement faults and seismic zones, induced by glacial loading and
unloading, are common in regions of hard bedrock.
The Glaciotectonic Map of North America is the result of
collaboration by more than 40 people from the United States and
Canada during the period 1989 to 1995. Aber et al. (1993) provided
a listing of most individuals. Key persons and their roles are listed below.
- James S. Aber: overall project coordinator.
- David L. Ackerman: supervisor of GIS data base and map production.
- John P. Bluemle: glaciotectonic compiler for north-central United States.
- Julie Brigham-Grette: glaciotectonic compiler for Alaska and Yukon.
- Lynda A. Dredge: glaciotectonic compiler for Arctic and eastern Canada.
- David J. Sauchyn: coordinator of GIS operation.
Data Base Structure
The data base was created in vector format on ARC/INFO, a
mainframe-computer geographic information system at the Spatial
Analysis Laboratory of the University of Regina. The data base
consists of the glaciated portions of Canada and the United
States, including continental shelves. The geographic base
contains several coverages, or layers, of data: basic geography,
topography, geology, and glaciation limits.
Basic geography and topography are available on
computer-compatible tapes (and other formats); they were obtained
respectively from: World Data Bank II (U.S. Federal Computer
Products Center) and U.S. National Geophysical Data Center (for
more information, go to NGDC).
Other coverages were manually digitized from a variety of published
Classification of Glaciotectonic Phenomena
A relatively simple classification scheme was developed for
glaciotectonic features. It proved difficult for contributors to
use a more complicated classification scheme, due to lack of
information or lack of time to evaluate each site. A simple
scheme was adopted, because the nature of published descriptions
and information sent by contributors varied substantially.
Many glaciotectonic features are known only from geomorphic
expression with limited, or in some cases no, outcrop or
test-drilling information. Conversely, detailed structural and
stratigraphic information are available in some areas. For
certain regions, neither contributions nor published information
were submitted for the data base. In some other areas,
contributors reported that nothing was known of interest. The
glaciotectonic data base is thought to be relatively complete for
the north-central and northeastern United States, Alaska,
Canadian Prairie region, Arctic Canada and eastern Canada.
Original documentation for the glaciotectonic feature entered
into the data base is given by more than 100 publications (see
Aber et al. 1993). Glaciotectonic data are contained in four main classes:
- Basement faults: faults or zones of seismic activity, created
or reactivated by glacial loading and unloading.
- Concealed (or buried) structures: folds, diapirs, faulted or
brecciated bedrock, and other glaciotectonic structures that have
no morphologic expression in the landscape.
- Ice-shoved hills: composite ridges, cupola hills, push
moraines, etc. Conspicuous morphologic expression, internal
structure of imbricated thrusts, overturned folds, diapirs, or
- Source basins: depressions from whence material was thrust
into adjacent ice-shoved hills, clear geometric relationship
between source depression and hill.
Map Scales and Feature Size
Scale limitations are a primary concern. Data were submitted in
various formats, including: descriptive tables, topographic maps,
aerial photographs, and published articles or maps. The map
scale most commonly used for submitting glaciotectonic data and
for digitizing was 1:250,000; larger and smaller scales ranged
from 1:24,000 to 1:500,000. The largest map scale likely to be
used for output in this project is 1:1,000,000; the smallest is
In view of these scale limitations, the minimum size feature that
we attempted to digitize in true shape is about 1 km².
Features smaller than this were entered simply as points; source
basins are also shown only as points in the approximate center of
basins. This means that no information on true size or shape was
entered for individual features smaller than 1 km².
Status of Glaciotectonic Mapping
All glaciotectonic, geographic, and geologic data have now been
entered as various coverages into ARC/INFO. Glaciotectonic data
were digitized from approximately 140 separate map sheets. These
are compiled into a single continental coverage, which includes
more than 300 point features (labels) and 500 area features
(arcs). This coverage may, of course, be updated at any time
that new or revised glaciotectonic information is contributed.
This will be especially valuable for those regions that are
poorly represented in the present data base, particularly the
The basic techniques were developed for combining various
coverages and designing small-scale map products. A subset of
geographic and glaciotectonic coverages for the northern Great
Plains was selected, including North Dakota, southern
Saskatchewan, and adjacent areas. The most troublesome map
design problem was how to portray those areas which contain many
glaciotectonic features that are too small to show in true shapes
as individuals at small scale. Our solution to this problem was
to use a special outline symbol to represent areas with many
discrete features. This map was published at scale 1:2,500,000
by the North Dakota Geological Survey (Aber et al. 1991).
We have combined the glaciotectonic data with other geographic
and geologic coverages for the continent to produce a master data
base for map production. Plots were initially developed with the
map region divided into four roughly equal quadrants (NW, NE, SE,
SW) in a commom projection at 1:3,000,000. This format proved
awkward because of its large size. Through a series of
revisions, the map has been reduced to a single sheet (E-format)
at a scale of 1:6,500,000. The map projection is Lambert conformal
conic with standard parallels of 49° and 77°. This map and
accompanying text are published by the Geological Society of America
(Aber et al. 1995).
The digital data are also available in ARC/INFO export format
along with ArcView project files for viewing the data files.
The advantage of this approach is that digital data retain the
full resolution as originally entered into the data base. Users
will be able to access and manipulate data directly. These files
are available for on-line FTP--see digital data.
- Aber, J.S., Bluemle, J.P., Brigham-Grette, J., Dredge, L.A.,
Sauchyn, D.J. and Ackerman, D.L. 1993. Glaciotectonic data base
and mapping of North America. In Aber, J.S. (ed.),
Glaciotectonics and mapping of glacial deposits. Canadian Plains
Research Center, Canadian Plains Proceedings 25/1: 177-200.
- Aber, J.S., Bluemle, J.P., Brigham-Grette, J., Dredge, L.A.,
Sauchyn, D.J. and Ackerman, D.L. 1995. Glaciotectonic map of
North America, 1:6,500,000. Geological Society of America, Maps
and Charts Series, MCH079.
- Aber, J.S., Bluemle, J.P., Sauchyn, D.J. and Ackerman, D.L. 1991.
Great Plains glaciotectonics. North Dakota Geological Survey,
Misc. Map 31, 1:2,500,000.
For more information, contact J.S. Aber, firstname.lastname@example.org
Last update March 2009.