Glaciotectonic landforms
Glaciotectonic landforms are the morphologic expressions of subsurface
structural deformations brought about by glaciation. Such landforms range
from conspicuous ice-shoved hills, to smoothed plains, to anomalous
depressions (Aber, Croot and Fenton 1989). These landforms may display their
original glaciotectonic morphology, where little modified by later events.
More commonly, however, subsequent glacial or nonglacial erosion or
deposition has altered the initial landform, in some cases obliterating any
morphologic expression of the ice-pushed structures. In all cases, some
knowledge of subsurface stratigraphy and structure is invaluable for
properly interpreting the landforms.
Glaciotectonic landforms may be divided in two general categories on the
basis of their morphostructural attributes.
- Ice-shoved hills – constructional hills,
ridges, or moraines that rise above the general landscape as a result of
structural uplift of deformed rock and/or sediment material. Includes
hill-hole pairs, composite ridges, push moraines, and cupola hills.
| View over crest of Prophets Mountains, North Dakota. Prophets Mountains is a large
ice-shoved hill that rises nearly 100 m above the surroundings. The interior
consists of deformed upper Cretaceous and lower Tertiary bedrock along with
glacial sediments. |
| View over the crest of the northern Dirt Hills looking westward. The rural road rises and falls over ice-shoved ridges that trend north-south. Each ridge is cored by uplifted Cretaceous bedrock and covered by glacial sediments. These are among the largest composite ridges in the world; the hills cover several 100 km2 and rise more than 200 m above undisturbed bedrock of the Missouri Coteau, southern Saskatchewan, Canada. Kite aerial photograph adapted from Aber and Aber (2025, 2026).
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- Glaciotectonic plains – subdued, streamlined, or smoothed plains.
Underlying structures include flat rafts or megablocks, intrusions and diapirs,
as well as buried ice-shoved hills and structural basins.
| Megablocks of deformed Cretaceous sandstone exposed along bluff of the Old Man River, near Tabor, southern Alberta. The source and distance of transportation for these megablocks are unknown. Note flat glacial plain on upland surface and people at base of megablock. |
| Jumbled mass of crushed bedrock material in the core of a recumbent fold, near top of section along bluff of the Old Man River, southern Alberta, Canada. All photos © J.S. Aber. |
These forms represent ideal types within a continuous spectrum of
glaciotectonic phenomena. Intermediate, transitional or mixed forms exist
between these ideal types and are in fact rather common. The materials of
which these landforms are constructed may be classified in three groups:
(1) pre-Quaternary strata, that are usually consolidated to some degree,
(2) pre-existing Quaternary strata, both glacial and nonglacial, and (3)
penecontemporaneous glacial sediment, that was deposited and deformed
during the same glaciation. Most glaciotectonic landforms contain all
three types of material in varying proportions.
Hill-hole pair – this is the simplest and most
instructive type of ice-shoved landform. It consists of an ice-scooped
basin and related hill. Other kinds of ice-shoved
hills are variations of this fundamental form. These hills were often
misidentified as kames or bedrock outliers, depending on their internal
composition. Bluemle and Clayton (1984, p. 284) described the hill-hole
pair as, "a discrete hill of ice-thrust material, often slightly
crumpled, situated a short distance downglacier from a depression of
similar size and shape."
The depression is the source of material now in the hill, and ideally the
volume of the depression should nearly equal the hill's volume.
Depressions are now often the sites of bogs, lakes, or estuaries, and so
their apparent sizes are often reduced by later sedimentation. The
ice-shoved hills may also have been altered by later erosion or deposition,
so an exact volume correspondence does not always exist between the hill
and related hole. Hill-hole pairs are now widely recognized in many
different settings.
| Small hill-hole pair at Anamoose, central North Dakota. Lake basin in foreground
is the source depression for material shoved into the hill in the background.
View in the downglacier direction. Anamoose is a classic locality for this
type of landform in North America (Bluemle and Clayton 1984). |
| Devils Lake Mountain, a large hill-hole pair in northeastern North Dakota. The lake basin in the foreground is the source for materials shoved into the hill behind the lake. Helium-blimp aerial photograph; all photos © J.S. Aber.
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The most typical and distinctive glaciotectonic landforms are ice-shoved
ridges found in many glaciated plains. Prest (1983, p. 45) aptly described
such ridges as, "a composite of great slices of up-thrust and commonly
contorted sedimentary bedrock that is generally interlayered with and
overlain by much glacial drift." Composite ridges typically display
multiple, narrow ridges separated by steep-sided valleys. The ridges are the upturned ends of thrust blocks or the crests of folds. Maximum uplift of thrust blocks may be >200 m, although in many cases no more than 100 m of uplift is present.
Composite ridges – large composite ridges (>100 m high) usually include a substantial volume of pre-Quaternary bedrock. Small composite ridges (<100 m high) may or may not include deformed bedrock; many, in fact, are composed largely of unconsolidated Quaternary strata. The term push moraine is commonly and loosely used to refer to ice-shoved ridges. Push moraines are a restricted subset of composite ridges that consist largely or wholly of glaciogenic strata (Chamberlin 1894; Aber and Aber 2026). Composite ridges that contain appreciable nonglacial (bedrock) material should not be called push or end moraines.
The typical morphology and structures of composite ridges are displayed quite well in the Limfjord district of northwestern Denmark (Klint and Pedersen 1995; Pedersen 1996; Aber and Ber 2007). Paleogene bedrock and drift were folded and thrust into composite ridges during late Weichselian glaciation. The bedrock, consisting of clayey diatomite interbedded with volcanic ash layers, was especially susceptible to ice-push deformation. Large, overturned, rootless folds of bedrock and drift were thrust up forming ridges. Ice-shoved hills display valley-and-ridge topography, in which maximum elevations are up to 100 m above the nearby floor of the Limfjord estuary.
| Left – view across the Limfjord toward Hanklit, a cliff exposure on the island of Mors. The cliff is about 60 m high and cuts across the end of a large ice-shoved hill. Right – ice-shoved hill inland from Hanklit. Narrow valleys alternate with ridges. Maximum elevations are 100 m above the floor of the Limfjord estuary, which was the source basin for material now thrust into the ice-shoved hill.
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| Hanklit reveals an overturned, rootless fold of Fur Formation (Paleocene) bedrock, wrapped by glacial gravel, and resting on till, as seen in 1979. Overview (left) and close-up shot of fold core (right). Note extreme stretching and plastic deformation in the fold core (*) as well as a fault along the fold axial plane (^). Ice movement was from left to right. All photos © J.S. Aber.
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Kite aerial photographs from the Limfjord region, Denmark.
Brandon Hills are a push moraine located on the Manitoba Escarpment of
southwestern Manitoba, Canada. The hills contain a core of deformed stratified drift
with a discordant cover of till. The internal structure consists of fault
blocks or slabs of stratified drift varying from sand to cobble gravel;
no bedrock or preglacial strata are present in Brandon Hills. Brandon
Hills occupy a rectangular area roughly 10 km east-west by 4 km north-south
and reaching an elevation exceeding 590 m. Composite-ridges
covered by a thin veneer of till resemble a giant fishhook in overall plan.
A conspicuous esker resting on till loops over the eastern end of the hills,
and low kames and kettles are located to the southwest.
| View northward toward the distal (downglacier) side of Brandon
Hills, southwestern Manitoba. Brandon Hills are a push moraine composed entirely
of deformed glacial sediments. Lake in foreground occupies a kettle hole
south of Brandon Hills. |
| Steeply tilted and faulted glacial sand and gravel within Brandon
Hills. The whole interior of Brandon Hills consists of such dislocated stratified
sediments, which were deformed when an ice lobe advanced into its own
outwash gravels. Scale pole marked in feet. |
| Discordant till covers the ice-shoved ridges of Brandon Hills.
The till is sandy and contains rounded cobbles that were reworked from deformed
stratified sediment of the underlying ridges. Scale pole marked in feet. All photos © J.S. Aber.
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Cupola hills – many glaciated hills have the internal structure of ice-shoved ridges, but lack a hill-hole relationship or the typical morphology of composite ridges. A distinctive hill of this type is the cupola hill. Such hills have an internal structure similar to composite ridges, but their external morphology was substantially modified by overriding ice. Cupola hills have three basic attributes.
- Interior structure – deformed glacial and interglacial strata with or without displaced and deformed floes of older bedrock.
- External form – long, even hill slopes with dome or drumlin morphology, varying from nearly circular to elongated ovals in plan, 1-15 km long, 20 m to >100 m high.
- Discordant till – overridden by ice which truncated deformed structures and deposited a basal till cover over the hill.
Cupola hills represent the combined effects of glacial deformation and subglacial erosion, deposition and molding of the ice-pushed hill. Where subglacial modification is slight, a subdued composite-ridge morphology may be preserved. With more modification, a rounded, smoothed cupola hill results. Still greater subglacial erosion and deposition may create streamlined, drumlin-shaped hills, and eventually all trace of the ice-shoved hill may be removed. The typical characteristics of cupola hills are demonstrated at Hvideklint on the island of Møn, southeastern Denmark (Aber 1979).
| Hvideklint cliff section on the island of Møn, southeastern Denmark (left). Large masses of upper Cretaceous chalk are thrust and deformed along with older glacial sediments. Cliff stands ~20 m high. Kite's-eye view inland from Hvideklint (right). Gently rolling terrain gives little morphologic indication of the strong glaciotectonic disturbances beneath this cupola hill (Aber and Aber 2026).
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| Intensely folded and contorted chalk, till, sand and gravel comprise the internal structure of the Hvideklint cupola hill. All materials are dislocated beneath a brown discordant till at the top of these cliff sections. These spectacular structures demonstrate the power of glaciotectonism. Scale pole ~1.5 m long.
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Drumlins – Many drumlins have disturbed cores and are, thus, at least partly glaciotectonic in origin. These drumlins are types of cupola hills that have been heavily modified by an overriding glacier (Aber and Ber 2007). Some of the most famous glaciotectonic sites are, in fact, drumlins.
| Exposure of a typical drumlin in east-central Wisconsin. Note the large overturned fold with red-brown till (right) wrapped around a core of deformed sand. Ice movement was left to right. All photos © J.S. Aber. |
| Overview of Saadjãrve Drumlin Field, southeastern Estonia. View toward northwest over a single, long drumlin to right with Lake Saadjãrve to left. Drumlin-forming till and stratified drift in the distal portion of the field display folds, thrust faults, and intense contortions (Rattus and Kalm 2001, 2004). Kite aerial photo by J.S. and S.W. Aber. |
| Ristinge Peninsula on the island of Langeland, southern Denmark. The peninsula is a
large drumlin that trends SE to NW and is cored by a series of upthrust and stacked fault blocks
consisting of Eemian and Weichselian strata. Left - kite aerial photograph looking toward the northwest (Aber and Aber 2026). Below - schematic section for central portion of Ristinge Klint showing tilted and stacked fault blocks of Quaternary strata. Direction of ice pushing from right to left. Adapted from Sjørring et al. (1982). |
Murtoos – Murtoos are newly described subglacial landforms created beneath an inferred wet-based ice sheet. Triangular, chevron, or lobate shapes consist of till and sorted sediments that are deformed in many cases (Seppälä 2016). Since their recognition based mainly on high-resolution LiDAR imagery, murtoos have received numerous investigations during the past decade, particularly in Finland and Sweden (e.g. Mäkinen et al. 2017), the Gulf of Riga between Estonia and Latvia (Karpin et al. 2023), and on the the Fraser Plateau in central British Columbia, Canada (Sodeman and Brennand 2025).
| Example of typical murtoos in vicinity of the Kynäsjärvi (Ky) site in southwestern Finland. LiDAR DEM, shaded-relief, oblique view looking westward. Note the triangular and lobate types of murtoos. Adapted from Mäkinen et al. (2023, fig. 2a); Creative Commons 4.0.
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Murtoos are typically triangular in shape, 30–200 m in length and width, and commonly <5 m in height. Excavations reveal that murtoos are composed of diamicton and stratified sediment. The cores typically display slightly deformed and dislocated to highly deformed sediments with various faults, folds, convolutions, and clastic dikes. They are associated with other subglacial meltwater features some 40-60 km behind the active ice margin. During and shortly following deposition, the murtoo sediments were deformed by active movement of overriding ice. On this basis, murtoos must be added to the list of distinctive glaciotectonic landforms (Aber and Aber 2026).
Model for ice-shoved hills
A model for glaciotectonism consists of two stages: (1) proglacial
thrusting of ice-shoved hills, followed by (2) subglacial modification of overridden hills. Initial proglacial thrusting takes place along a décollement that may be controlled by any of several
features such as lower boundary of permafrost, lithologic or stratigraphic
boundary, position of confined aquifer, etc. Subglacial meltwater
may either erode tunnel valleys or deposit eskers, while proglacial meltwater may cut spillways across the ice-pushed ridge and deposit outwash sediment on the distal side of the hill.
| Schematic model for glaciotectonic deformation of ice-shoved hills. Not to scale; adapted from Aber and Ber (2007).
A – initial proglacial thrusting of fault blocks over some type of décollement that is lubricated by high-pressure groundwater. Near-horizontal thrusts curve upward to the surface, but only slight displacement of faults has taken place at this stage.
B – continued glacier advance and growth of an ice-shoved hill at the ice margin. Thrusts become steeper and overturned folds may develop with secondary faults. Ice-contact sediment and outwash begin to accumulate from above and basal till from beneath the glacier. Composite ridges are the result. Meltwater may erode spillway valleys across the hill.
C – advancing glacier overrides the hill with complex folding, faulting, and brecciation in the upper portion of the hill. A discordant layer of till is deposited across the hill top or erosion of the hill top could take place. Cupola hills or drumlins are the result. Meltwater might erode tunnel valleys or deposit eskers (not shown), and murtoos may form some distance behind the active ice margin (not shown).
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Debris flows, small fans, ablation till and other surficial sediment may accumulate at the ice margin, while basal till may build up under the glacier. Such sediments often become deformed as ice movement proceeds. With continued glacier advance, the hill may be overridden with further subglacial deformation, erosion, covering with till, and/or molding into a cupola-hill or drumlin. All traces of the ice-shoved hill may be eventually removed by prolonged erosion.
Large ice-shoved ridges are topographically and structurally similar to such thrust and folded mountain belts as the Canadian Rockies or Swiss Alps that were formed by thin-skinned plate tectonics.
The only real difference is size, ice-shoved ridges being one or two orders of magnitude smaller than true mountains (Berthelsen 1979; Aber, Croot and Fenton 1989).
| Strongly folded sedimentary strata of Mount Kidd, Kananaskis Mountains,
Alberta. The style of deformation exhibited in the Canadian Rocky Front
Range is identical to that of ice-shoved ridges; the only real differences
are size of structures and timespan of deformation. |
| Large overturned, tight fold of Mesozoic carbonate strata in the Helvetic Alps, near Lütschental, central Switzerland. Kink bands appear on both limbs of the fold, and the fold axis (*) is clearly visible. All photos © J.S. Aber.
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Glossary or references.
Brittle glaciotectonic structures 
Ductile glaciotectonic structures 
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