Sedimentary Geology, 62 (1989) 349-355 349 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

Drumlins and flutings in Finland" their relationships to ice movement and to each other

OLAVI H E I K K I N E N 1 and MATTI T I K K A N E N 2

University of Oulu, Department of Geography, SF-90570 Oulu (Finland) 2 University of Helsinki, Department of Geography, SF-O0100 Helsinki (Finland)

Received December 1987; revised version received May 1988

Abstract

Heikkinen, O. and Tikkanen, M., 1989. Drumlins and flutings in Finland: their relationships to ice movement and to each other. In: J. Menzies and J. Rose (Editors), Subglacial Bedforms--Drumlins, Rogen Moraine and Associated Subglaeial Bedforms. Sediment. Geol., 62: 349-355.

Drumlin fields are numerous and widespread in Finland and flutings are common in the same areas. The impressive Kuusamo drumlin field in northeastern Finland covers older drumlins whose features are evident from beneath the

younger till bed. In many cases the orientations of the ovedying younger streamlined forms deviate from the orientations of the forms lying beneath them.

The majority of drumlins and flutings form fan-like patterns reflecting the configuration of active ice lobes. The orientations of the smallest fluting ridges vary in places more than those of the drumlins in the same area. It is

suggested that small flutings tend to denote the youngest direction of ice movement. Bending of some drumlins and flutings indicates a curvilinear motion of the ice, and some drumlins with forks pointing in a slightly different direction

were perhaps caused by a slight shift in ice movement. Large groove-type flutings in the bedrock took a great deal of time to develop and do not therefore always show the direction of ice movement during deglaeiation.

Introduction

Large drumlin fields have been described in southern Finland (Aartolahti, 1966, 1968) and in central Finland, where the Pieksiimiiki and Keitele fields, covering approx. 25,000 km 2, comprise a total of about 14,500 drumlins (Gltickert, 1973). The fairly accurately documented Kuusamo drumlin field in northeastern Finland has been calculated to contain 2400 drumlins in an area of 3700 km 2 (Gltickert, 1974). A number of investiga- tions have also been carried out in drumlin areas in Lapland (Kujansuu, 1967; Heikkinen and Tik- kanen, 1979; StrUm, 1980). This paper summarizes numerous observations and provides some general conclusions regarding the relationship between drumlins and flutings and ice flow movement.

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Drumlins and flutings are streamlined glacio- genic landforms indicative of the direction of ice movement at the time of their deposition. Drum- lins and depositional fluting ridges are usually composed of till, although the former in particular may contain a quite substantial bedrock core. Erosional flutings, or grooves, on the other hand, can be exclusively bedrock forms. In Finland there is commonly a gradational series from narrow flutings to wider drumlins, and there are places in northern Finland, for instance, in which the two types of landforms are superimposed one upon the other, so that the drumlins are fluted (Aario et al., 1974, p. 8; Aario, 1977c, pp. 5-6; Heikkinen and Tikkanen, 1979). Aario (1977a, b, c) notes in his work in northeastern Finland that active ice hum- mocks and transverse Rogen moraines (ribbed

351)

moraines) belong to the other end of the same transitional series of glacial bed forms.

It is difficult to make a strict demarcation

between drumlins and flutings. Gliickert (1971, 1973, 1974) in particular has made an inventory of

the drumlins of Finland and classified them into various types.

Flutings are usually described as ridges where the investigator has regarded them as accumula-

tion forms and as grooves where they have been taken as erosional forms (Kujansuu, 1967, p. 31;

Heikkinen and Tikkanen, 1979, p. 1). Proximal

troughs (see Lassila, 1986), or crescentic troughs,

located on the proximal sides of bedrock hills, are

also fairly common in association with drumlins. These have been described in the Koillismaa re-

gion of nor theas tern Finland (Aario and ForsstriSm, 1979).

Formation and orientation of drumlins and flutings

the drumlins were created (Heikkinen and Fik- kanen, 1979, pp. 9 10).

The effects of the topography on ice movement and the orientations of the flutings towards the

end of the deglaciation are also interpreted from the many fluting ridges in northern Lapland that are curved in shape (Heikkinen and Tikkanen,

1979, p. 10). Slight bending of drumlins due to the curvilinear motion of the ice also occurs in Kuu-

samo in northeastern Finland. Here forked drum- lins are also found, with their forks pointing in slightly different directions. It is probable that

such forks were caused by a slight shift in the direction of ice movement (Aario et al., 1974, pp. 15, 17).

In general it seems that large flutings are usu-

ally of the same orientation, and possibly the same age, as the drumlins in the same area, whereas those flutings with a different orientation are usu-

ally smaller in size and may be younger than the

Most drumlins and flutings were evidently formed in the inner marginal zone of the continen- tal ice sheet during the final retreat phase (Aario

et al., 1974; see also Aartolahti, 1968, p. 26). Conditions apparently became favourable for their

creation when the relatively thin ice began to flow

more rapidly in the depressions than over the

bedrock protrusions (Aario and ForsstriSm, 1978,

p. 46, 1979, p. 21). It has been suggested that

narrow flutings develop closest to the ice margin, drumlins slightly further into the ice sheet and still

further from the edge transverse till mounds and ridges form (Aario, 1977a, b). Punkari (1982b, p. 5) concludes that drumlins were laid down chiefly

in a zone 20-100 km inside the receding ice margin. Flutings are to be found on top of drumlins in

some places, e.g. in northern Lapland, where their orientations deviate in places from those of the somewhat older drumlins beneath them. In north- ern Lapland the younger origin of flutings may also be deduced indirectly from the fact that their orientations vary considerably more than those of the drumlins in the same area, presumably be- cause the local topography was able to influence the directions of ice flow to a greater extent during deposition of the flutings than at the time when

SWE

Fig. 1. Principal drumlin fields in Finland and their orienta- tions, chiefly after Punkari (1982a, b). The map also contains

certain major ice marginal formations such as the First, Second

and Third Salpausselk~i ( S S 1, SS 11, and S S 111). The shaded

zone crossing northern Finland marks the ice divide which

formed the boundary of the Fennoscandian Ice Sheet at the end of the last glaciation. The sites of Figs. 2 -6 are also indicated.

351

1 2 4 "' ~11 " 5

Fig. 2. The Uimaharju-Suomu ice marginal formation crossing a drumlin field in Eastern Finland (cf. Fig. 1). 1 = drumlin, 2 = ice

marginal formation, 3 ffi extramarginal channel, 4 = mire, 5 = lake and river.

drumlins and large flutings. It is possible that flutings became progressively smaller as deglacia- tion advanced, reverting from large-scale forms to small-scale ones of the kind seen in front of mod- em glaciers. Generally it seems that the smallest flutings denote the youngest direction of ice move- ment (Heikkinen and Tikkanen, 1979, pp. 9-10).

In contrast to fluting ridges, the large groove- type flutings created in the bedrock by erosion would have required longer periods of time for their development, and thus they do not always correspond in orientation to the direction of ice movement at the end of deglaciation. The large grooves located on the fell of Jeiiqeloaivi in Lap- land, for example, began to develop during the glaciation, well before the deglaciation phase had begun (Heikkinen and Tikkanen, 1979, p. 10).

Also eskers and end moraines may reveal the relative chronology between them and drumlins. In many places in Central and Southern Finland

eskers run across the drumlin fields, and there are also cases in which end moraines are found on top of drumlins (Gliickert, 1973; Aartolahti, 1968, p. 27).

Fig. 2 shows a situation in which the Uimaharju-Suomu marginal formation, usually looked on as an eastern continuation of Salpaus- selk~i II, crosses a drumlin field in southeastern Finland.

Factors determining the regional and local occur- rence of drumlins and flutings

The majority of drumlins in Finland are con- centrated in areas occupied by active ice lobes during the deglaciation (Fogelberg and Sepp~l~i, 1979; Punkari, 1982a, b; Kujansuu and Niemel~i, 1984; Sepp~il~i, 1986). Drumlins, flutings and other streamlined forms present fan-like patterns which reflect the configuration of these ice lobes (Figs. 1

35!

- - _ F I N L A N D T""'.-...~ U S S R --.._ ~ I

~_ . . . . . " ' - - . - ~ ~ ( ~ ~ ~ . . L . ~ x ~ ~ ~ Kesk,-Ku,,,& I

. . - - - ---

' ""- , \ ' 1

KUUSAUO o... LL~"° ,~S'----'-----~ ~ % ~ l'I

K o s t o n l d r w . . ~ Y/ " el¢l - u o p p a l a r v l :

"o~. ;L ~ , \ ~rm~ig.4~,.., - " _~.~ & ~_ "~

,,,.~ :::.:..::.: ............. ~:_ --..:, ',, , .% \ ~ . ~,,,~ ~,~

• . . ".:.:.:...:.,.... . . . . . . . . . . . . . __~ r~ lJ i t~ i . . .

, / ///// .~,,; -- i= i ~ l l i A M n - ~ ' U S S R Kesk,-Kuittij. 7////'/.~@/

PUOLANKA ~J~SUOMUSSALMI -- / ~ " ' ~ ~ n ~ I ~ 0 ~ ' ~ ' ~ ~ - - - - c ' ~

Fig. 3. A. Regional pattern of glacial flow at the time when the Tuoppaj~'vi lobe was active. B. Regional pattern of glacial flow

during a later stage in the deglaciation, when three ice lobes existed on the Finnish side of the border, the Kuusamo, Oulu and Ranua

lobes, each with its associated drumlin field. These covered the drumlins formed by the Tuoppaj~rvi lobe in places (cf. Figs; l and 4).

Map slightly modified from Aario and Forsstr6m (1979).

and 3), and it is therefore natural to assume that they were created towards the end of the glacia- tion under the advancing ice flows (Gliickert, 1973, p. 19). The areas of passive ice between the ice lobes do not contain any appreciable drumlin fields of fluting forms (Punkari, 1980, p. 308). Since the ice lobes often differed greatly in their

directions of ice movement, drumlins in different parts of the same interlobate zone vary in orienta- tion by as much as 90 ° (Punkari, 1982b, p. 3; Figs. 1 and 3).

Substrate topography frequently has a consid- erable effect on the location of drumlins and flutings. Often they are to be found on convex-

353

3 4 5 " " ' - " '

Fig. 4. The impressive drumlin and fluting field created by the Kuusamo ice lobe, below which one can still perceive older drumlin forms derived from the Tuoppaj~vi ice flow, which differ slightly from the former in direction (cf. Figs. 1 and 3). 1 = old drumlin, 2 = younger drumlins and flutings, 3 = esker, 4 = lake and river, 5 = national boundary.

shaped ground, whereas hummocky and Rogen moraines favour concave valleys and depressions

(Aario, 1977a, b). Many drumlins in Southern and Central Finland occur on more or less flat ground lying slightly above their surroundings or on gently rising terrain (Aartolahti, 1968, p. 26; Glilckert,

1973, p. 20). In some places they may be present on slightly inclined distal slopes, but not usually in valleys or basins. In his study of the Pieks~im~ki drumlin field in Central Finland Gliickert (1973,

p. 19) suggests that the rate of ice movement slowed down as the ice was forced uphill in the proximal part of the drumlin field, giving rise to

short, rocky drumlins, but where the ice flowed gently downhill its rate of flow increased and the till ridges became longer, narrower and lower.

Many well-developed fluting patterns on lee slopes

also occur in northeastern Finland (see Aario et al., 1974, p. 27) and Lapland (Kujansuu, 1967, p. 31).

t

Bedrock protrusions constitute a barrier to ice movement resulting in spiral flow in the plastic

basal ice at the proximal end of such a protrusion, which then follows the outlines of the edges of the bedrock formation. This spiral flow has a pro-

nounced erosional effect on the up-ice end of the

protrusion at the same time as the linear ice flow higher in the ice is smoothing the top surface (Aario, 1977a, c). This may explain the formation of proximal or crescentic troughs in front of be- drock protrusions and drumlins with a bedrock

core. It would seem that most of the proximal troughs date to a large extent from the maximum phase of glaciation, and it has even been conjec-

~54

Fig. 5 Well-developed drumlin ridges and intervening strips of aapa fen in Kuusamo (cf. Fig. 1). These drumlins were formed by tile action of the Kuusamo ice lobe. Photograph: Risto

Aano, reproduced by courtesy of the Finnish Army Map Service.

tured in Sweden that they could be the outcome of several glaciations, since they evidently can easily survive interglacial periods (Lassila, 1986, p. 139).

An example from northeastern Finland

The drumlin fields of northeastern Finland were first investigated some time ago (Hanninen, 1915; Virkkala, 1951). Later descriptions of drumlins in the area were linked very strongly with the ice

lobe systems prevailing during the deglaciation (see Kurimo, 1974, 1978; Aario and Forsstrrm, 1978, 1979; Punkari, 1982a, b). Evidence from striae, glacial landforms and the till stratigraphy suggests the existence of a number of ice lobe flows in the region.

The lobe reconstructions depicted in Fig. 3 are those proposed by Aario and Forsstrrm (1978, 1979). In their interpretation the oldest formations in the region were derived from the deglaciation phase associated with activity in the Tuoppaj~irvi lobe, at a time when the whole region was covered by this single lobe flowing in from the west. It is at this time that the particularly striking Tuoppaj~irvi drumlin field in the Soviet Union was created. Drumlins also arose in the area now lying within Finland, e.g. at Kuusamo, but these were later largely obliterated by the action of the Kuu- samo ice lobe (Fig. 3).

The TuoppajLrvi flow later divided into three more or less simultaneous ice lobes, those of Kuu- samo, Oulu and Ranua. These three, which may well have developed around the time of Salpaus- selk~i II, about 10,500-10,200 yr B.P., gave rise to a corresponding set of three drumlin fields (Fig. 3B).

O-IOta ~ 10-20m i m l 20-30m I ~.30 rn

Fig. 6. An impressive proximal crescentic trough in Kuusamo, eastern Finland (cf. Figs. 1 and 3). For details, see text.

The Kuusamo lobe terminated in the P~i~ijiirvi marginal complex, and formed the impressive Kuusamo drumlin field (Figs. 4 and 5), as is excellently, described by HLnninen (1915). It was this lobe~that covered the older drumlin field created at the time of the Tuoppaj~irvi lobe. The features of the old drumlins are still reflected in the material beneath the younger till bed, although Aario et al. (1974: fig. 3) interpret these as a "local tectonic orientation". The younger drum- lins and flutings laid down by the Kuusamo lobe differ markedly in orientation from the older drumlins (Fig. 4). Boulton (1987) has described a very similar situation from Victoria Island, Canada, where large early drumlin masses trend- ing 1.70 ~' ---, 350 o, are superimposed by a later and smal.11e~'2drumlin set orientating 15 o _._, 195 o.

One of th~dnany proximal troughs in the Kuu- samo drumlin field, that of Pyhiivaara, is pictured in Fig. 6. It is now partially filled by the waters of the crescentic Lake Pyhiijiirvi, which is over 30 m deep in places. The altitudinal difference between the lake bottom and the crest of the nearby hill of Pyhiivaara is over 100 m. The crescentic shape and the position in relation to the ice movement of this proximal trough as well as the depth contours in the lake allow us to conclude that it was gouged out mainly by an ice flow from the west. At that time glaciation was still at its maximum. The sinuosity of the contours, especially in the north- western part of the area depicted in Fig. 6, like the sinuosity of the shoreline of Lake Rukajarvi, re- flects streamlined forms in the till cover laid down only during the younger Kuusamo flow phase, the ice movement of which had little impact on the shape of the proximal trough.

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