Northern Kettle Interlobate Moraine
The Northern Kettle Interlobate Moraine is, as the name implies, a moraine with numerous kettles, formed between two lobes of icethe Green Bay and Lake Michigan Lobes (Alden 1918:308-309) (Figs. 1, 2, 4, 16, 17). The moraine contains a variety of glacial features some of which were among the first in the country to be well described (Chamberlin 1877:199-246, 1878) and which remain today among the best in the world. Glacial features are well represented in the Northern Kettle Moraine State Forest which extends from the vicinity of Glenbeulah in Sheboygan County southwesterly and then southerly 20 miles to the vicinity of County Highway H about 3 miles south of Kewaskum in Washington County (Figs. 1, 4, 17). The forest encompasses much of the area along the common boundary of Fond du Lac and Sheboygan counties. The area recommended for inclusion in the Reserve includes the entire Northern Kettle Moraine State Forest plus Principally an area within the north-central part that is not now in the forest. The recommended addition contains one of the most striking groups of moulin kames (conical hills of drift deposited under the ice) to be found anywhere in the world (Fig. 17). [Moulin (moulan) Fr., is defined by Webster's dictionary as a nearly vertical shaft in a glacier into which a stream of water pours. The debris carried in by the water is piled up at the base of the moulin, building the moulin kame.]
The Interlobate Moraine was mapped by Alden (1918) as part of a reconnaissance in southeastern Wisconsin and has hardly been touched since. Much study is needed to understand fully the history of individual forms or even of many large units. Different interpretations are possible within the framework of existing data. However, it seems clear that several at least local fluctuations of the two lobes were involved during Woodfordian time. The junction thus is a zone of partial mixing or interstratifying of material from each lobe. Outwash gravel and other glacial deposits were reworked and redeposited, commonly on preexisting ice, as the junction shifted back and forth.
The area is so large and diverse that it is not feasible nor necessary for purposes of this book to describe each feature. Rather, the area is subdivided into mappable units or groups of similar geomorphic features (Fig. 17). These are not pure units because of the almost infinite detail available within any relatively small segment of the forest. Nonetheless they serve to emphasize such features as end moraines and stagnate-ice or "dead-ice" moraine of knob and swale topography, moulin kames, outwash, eskers, crevasse fills, kettles, and the like. These and other features are described more fully later.
Because of its variety and superb development of "textbook" features, its proximity to centers of population and heavy recreational use, and its historical importance in the development of concepts in glacial geology, this area is one of the most important in the state that can be recommended for inclusion in the Reserve. It deserves every attention it can be given; the recommended expansion of the state -owned forest is absolutely minimal. Further expansion in spite of high land values is exceedingly desirable.
Numerous glacial features on all sides of the recommended area should be included in the Reserve even though they are similar to features within the recommended area. Because of their value for construction aggregates, many depositional glacial features have been destroyed, and others will be lost or modified unless they can be included in the Reserve. Other glacial features not likely to be altered significantly or lost to mankind if not included are also mentioned.
In 1876 Chamberlin orally presented a paper to the Wisconsin Academy of Sciences, Arts, and Letters on the extent and significance of the Wisconsin Kettle Moraine (Chamberlin 1878). In those days when great geologists were formulating principles of the concepts of glacial geology, Chamberlin was a true giant among them (Fenton and Fenton 1952). Although today some of his words and phrases are no longer popular and editors would cut and prune his remarks in order to save space, Chamberlin's description of the moraine bears the test of time so well that I feel compelled to quote him directly. In describing the surface form of the moraine he wrote:
Chamberlin was referring to the surficial features of the end moraine of what is now called the late Woodfordian or Cary ice as it was deployed through the entire state of Wisconsin and not just the interlo bate moraine in what is now the Northern Kettle Moraine State Forest. Nonetheless, his description can scarcely be improved upon for the recommended area. In speaking of the nature of the material, Chamberlin (1878:205) emphasized that ". . . all the four forms of material common to drift, vis: clay, sand, gravel, and boulders, enter largely into the constitution of the Kettle range, in its typical development. Of these, gravel is the most conspicuous element, exposed to observation." Chamberlin (1878:210) further recognized that most bedrock units in Wisconsin and Upper Michigan were represented in any one section of the drift, including native copper from Keweenaw Peninsula, but that the bulk of the drift was derived locally. Thus, most gravel is composed of the local white to very light gray Silurian dolomite (Fig. 3), well rounded by water work (Fig. 18).
However, we now know that more than one local advance of ice was involved, spanning probably several thousands of years, and that reworking of outwash gravel by later advances was commonplace. Hence, some constructional forms contain nonstratified gravel instead of till. Deposition of the gravel directly from ice without water working took place.
Other details of the moraine in Wisconsin were presented, and it was compared with its counterpart in other states (Chamberlin 1877, 1883a). In the latter paper, the term "interlobate moraine" was first introduced (Chamberlin 1883a:276) and properly diagnosed as to origin in contrast to normal medial moraines. A reconstruction of the ice flow directions (Fig. 16) demonstrates conclusively the lobate character of the ice and the opposing movements at the junction of the two lobes. This gross story has changed little in the intervening century.
Chamberlin's important role in the development of the concepts of glacial geology would not have been possible were it not for the clear observations and lucid writings of his predecessors of whom, in connection with the Kettle Interlo bate Moraine, only Charles Whittlesey will be singled out. It was Whittlesey who, in the mid-1800s, first recognized the "kettle moraine" and correctly interpreted the origin of the kettle holes (Fig. 19) to buried glacial ice rather than drifting icebergs as was in vogue at the time (White 1964). This was truly astonishing insight, and is but one of the major accomplishments of that amazing man.
The Greenbush Kettle, 2 miles south of Greenbush on the Kettle Moraine drive, has been favored with a geological marker sign for years. It is one of the most symmetrical deep circular depressions visible from the road. Many others are more irregular (Fig. 20) but just as typical, with or without water.
In brief the Northern Kettle Interlobate Moraine is conspicuous because of its more abrupt irregularity and sharpness of feature (Fig. 21) compared to the undulating ground moraine with smoothly contoured drumlins and till-covered bedrock rises on both sides (Fig. 22). The light-grey gravel of the Interlobate Moraine also contrasts markedly with the reddish brown and light yellowish brown sandy till of the ground moraine. Neither its maximum elevation (1311 ft at Parnell tower, sec. 10, T. 14 N., R. 20 E.) (Fig. 23) nor its general relief of 100-200 ft are significantly different from the till plains and drumlins adjoining. However, it is characterized by major lowlands at 950-1000 ft, such as that occupied by Long Lake (Fig. 24) and the East Branch of the Milwaukee River. The flatness of such lowlands and the abrupt rise of drift deposits flanking them also emphasize the glacial features (Fig. 25). Farming of the lowlands contrasts with the wooded drift hills to spice the view.
The Kettle Interlobate Moraine lacks an integrated drainage net work. Many closed depressions drain through the coarse gravel be low and do not need surface streams. Others intersect the ground water table and have perennial ponds or lakes. Elkhart Lake (Fig. 26), a large kettle north of the forest, with high land around it, drains westward to Sheboygan Marsh and the Sheboygan River. Crystal Lake, next south of Elkhart Lake, has no outlet. However, Mullet River flows by only 0.25 mile to the southwest in its arc around the north end of the Kettle Moraine Forest, and then southeasterly and eastward in a tortuous route to join the Sheboygan River at Sheboygan Falls. Interestingly those two rivers have adjoining headwaters, and their uppermost courses are parallel yet flowing in opposite directions about 1 mile apart northwest of Long Lake. Both rivers have very intricate courses to Lake Michigan, probably in part controlled by fracture patterns in the stagnating ice which permitted the supraglacial streams to superpose themselves on the underlying drift and bedrock. The East Branch of the Milwaukee River, flowing southward into the Milwaukee River southeast of Kewaskum, drains most of the Northern Kettle Moraine Forest proper. Its course follows the trend of the moraine and generally lies almost precisely on the reconstructed boundary between the two lobes of ice. (This is somewhat west of the boundary indicated by Alden 1918, Pl. III). Probably its origin dates back to the initial abutment of the ice of the two lobes where it developed in the axial depression along that junction. Apparently it has remained in that position since.
In the wastage of the Lake Michigan Lobe, however, additional channels were formed on the stagnating ice. Mink Creek lies in a channel that starts about 2 miles northeast of Parnell and flows generally southerly past Beechwood in a course with abrupt right-angle bends. These seem also to reflect the fracture pattern of the ice as the initial stream was let down on the surface below. Many other examples exist in the area, but no field study of any of them has been attempted. They need to be integrated into the history of the moraine.
Figure 17 shows the distribution of drift features that characterize certain parts of the area. For convenience in the classification each unit is named for the most abundant or striking feature or features it contains. These units are: ground moraine and drumlins, stratified drift, end moraine and stagnate-ice or dead-ice moraine, and special features such as moulin kames, eskers, and crevasse fills. Ground moraine with drumlins and till-covered bedrock rises (Fig. 22) comprise most of the area up-ice from the front of both lobes. Small stagnate-ice features in that unit are common, but only a few kames are shown on the map. The drumlins, fluted forms, and striae recorded by earlier workers and summarized by Alden (1918, Pl. IV) show clearly the former last movements of the ice of both lobes. Time has not permit ted me to add more field data. Even though the general deployment of ice shown by Alden (1918, Pl. IV) and by Chamberlin (Fig. 16) is not expected to be changed in gross form, detailed field work is needed to show ice movement in relation to individual segments of the moraine.
In and adjacent to the recommended area stratified drift, including outwash, glacial-lacustrine deposits, and other water-formed features (Fig. 27) are more prevalent than end moraine (Fig. 25) and stagnate-ice or dead-ice moraine (Fig. 28) formed more directly by the ice. The washed surfaces and deposits reflect in part the cleaner ice of the two lobes juxtaposed and in part the concentration of runoff along the junction of the two lobes. The normal surface gradient up-ice in each lobe would have led water to the junction of the lobes, from which its escape could only have been to the south along that junction. Such water-worked stratified drift varies in size from the coarse bouldery material of glacial streams to the sand, silt, and clay in ponded water. Drift obviously has formed in places on buried ice blocks to leave pitted outwash; elsewhere it seems that entire portions of stream beds or lake sediments have been dropped down as continuous ice below melted out. Most parts of the well-washed drift, however, were formed adjacent to ice, but not on it. Original stratification is preserved.
Even during deglaciation the widening and northward migrating gap between the two lobes effectively concentrated glacial-fluvial activity between the lobes. Thus it was the locus for many striking forms. Eskers (Figs. 29-32) and moulin kames (Figs. 33-37) formed under the stagnate ice by subglacial streams fed through moulins or openings through the ice sheet. Their subglacial waters also flowed toward that same gap. Crevasse fills (Fig. 28), topographically commonly like eskers, were formed in crevasses open to the sky in part by supraglacial streams and in part by mass movement of surface debris into the crevasses.
Moulin kames are scattered throughout and adjacent to the recommended area, but none is better developed or displayed than those in the group northeast of Long Lake. There, in the widest part of the washed drift area, are some of the best moulin kames to be found anywhere in the world. Beautifully conical hills, such as McMullen (Fig. 33), Garriety (Figs. 34 and 35), Connor and Johnson (Fig. 36), rise at the angle of repose of the material more than 100 ft above the flat, washed, drift plain surrounding them. Numerous smaller kames, only a few tens of feet high, are commonly less conspicuous among the drift ridges. Many are just as symmetrical as the larger ones in the lowlands (Fig. 37). Other more irregular moulin kames, such as Dundee Mountain, are also present and grade into crevasse fills or into ice-walled lake areas (openings so enlarged that lakes formed within the glacial ice walls). Such forms originated where melt waters on the ice dropped through moulins or crevasses, dumping their detritus at the base. Openings ranged from nearly vertical circular pipes (moulins) to very elongate fractures and rounded to irregular openings; commonly water and debris was fed into the fractures at more than one place along the sides and ends of crevasses, building irregular forms below the ice. Many large fractures were fed not just with running water, but also with mud flows, debris slides, and the like. Ponded water in some also trapped delta and lacustrine sediments. Thus, the material in such features as moulin kames and crevasse fills ranges from normal till, through the available sizes of water-transported material, to ponded sediments. The cross section of Garriety Hill is typical (Figs. 34, 35). It shows rounded to angular gravel, sand, silt, and clay deposited as unsorted till in irregular masses, and as sorted sediment in alluvial fans, pond sediments, and the like. Water that formed the northern group of moulin kames drained westward under the ice to join the drainageway through Long Lake Valley. Their channels are readily discernible on aerial photographs.
The end moraine and stagnate-ice or dead-ice moraine are not differentiated in Fig. 17 because of their general similarity of origin. The terms are used loosely here for lack of detailed understanding of their genesis. They might have been subdivided for descriptive purposes into those areas characterized by elongate ridges and valleys and those with circular knobs and swales. In the interlobate area all are believed to result from ice stagnation and the melting out of blocks of ice of the appropriate geometry to fit the surface depressions. Such geometry is predicated on the movement of the ice at the time the ice and debris were mixed, on its fractures, or on the manner of burial by overriding ice, outwash, debris slides, etc.
The detailed deployment of the moraines in the Northern Kettle Moraine Forest is of considerable interest in the reconstruction of events as related to the flow of ice. From the vicinity of Kewaskum north to Long Lake, the trend of the Interlobate Moraine is almost north. From Long Lake the Interlobate Moraine turns fairly abruptly to the northeast to Elkhart Lake where it again swings to the north. At least part of the explanation of the bend may lie in the topography of the bedrock which unquestionably has exercised some control on the deployment of the ice. The deep pre-glacial valley at Sheboygan Marsh must have provided relatively easy access for the ice of the Green Bay Lobe, leading it more rapidly and further to the southeast than was possible over the bedrock hills south of that marsh. They restrained the ice of the Green Bay Lobe, allowing the ice of the Lake Michigan Lobe to push farther westward. Such kinks and bends in the terminal area are commonplace along the entire late Woodfordian front. They are of considerable importance in under standing the development of the features found in the Northern Kettle Interlobate Moraine, but time does not permit their reconstruction here. Much field work is needed to unravel their history.
Small moulin kames in the stagnate-ice moraines are probably contemporaneous with the related features. However, the precise timing of the formation of the main group of moulin kames versus the main moraines to west and east is conjectural.
I hypothesize (Black 1970) that shortly after the two lobes butted together, the thickness of ice gradually increased from 100 to 300 ft at the start to a thickness perhaps of several thousand feet when the ice extended southward into the center of Illinois. Ablation (loss of ice) particularly by melting aided by a surface stream at the junction of the two lobes would be countered by ice movement from the base of the ice sheet diagonally upward to that junction at the surface. Upward flow at the terminal zones of glaciers is commonly at angles of 10-45° bringing debris from the base toward the surface to replace ice lost in the ablation zone and to maintain the surface profile of the glacier. When ice was at its maximum thickness at the junction, the basal debris may not have reached the surface. As the ice thinned during the waning of the Cary glaciation (late Woodfordian), it would intersect the surface. As thinning continued to perhaps 200 or 300 ft of ice, fractures aided by melt waters penetrated in favorable places to the bottom of the glacier. In them the moulin kames, eskers, and crevasse fills began to grow. However, at that time the thicker ice back from the junction was continuing to move forward even though the terminal zone was stagnate. The shear planes and flow layers that brought debris up from the base presumably angled obliquely downward and away from the actual surface junction of the two lobes to the general location of the main moraines on both sides of the inner washed area. At the locus of the moraines, basal ice and debris were interstratified by flow of ice while the basal ice closer to the junction was stagnated and remained relatively free of debris. Thus the two main moraines, one for each lobe, are in a sense end moraines even though they do not mark the terminal position of the ice nor were they deposited at the outer edge of the ice. They represent the outer edge of the active ice for each lobe and were separated by a zone of stagnate ice shaped like a very broad, low wedge with its apex upward, at least during the waning of the glaciation. It seems relatively clear that stagnation took place over much of the area because so many small ice-contact, washed-drift features are superposed on all other forms.
Many details of the reconstruction of the events that led to the surface features in the Northern Kettle Interlobate Moraine are imperfectly known. New topographic maps and aerial photographs unavailable to Alden (1918) now permit an analysis of surface forms to be made in far more detail than was possible for him in his reconnaissance study. Surface analysis, however, is only part of the story. Serious mistakes have been made in the past in the interpretation of glacial forms by morphology alone. Subsurface exploration must be carried on concurrently before a firm foundation can be laid that would permit us to change significantly the gross picture of the Kettle Interlobate Moraine as commonly accepted. Such detailed study has had little economic incentive, but should be under taken before gravel pit operations remove or modify evidence that might be the key to part of the story. A beautiful story can be constructed on evidence available, but an even larger part of the story is still unsupported in fact. The prospects in future study are especially intriguing.
Thus, in brief, the heavy use of the area for recreation and consequent loss of land for cottages and commercial development require our immediate action to preserve many glacial forms, like kames, eskers, and stagnate-ice features. Demands for gravel are increasing and many glacial forms are being removed in toto. We must protect not only the many striking forms but also the "normal" forms now before they are exploited. Many shown in the mapped area (Fig. 17) are outside of the recommended area. It is hoped that some of the better ones ultimately will find their place in the Reserve. If not, the gravelly deposits will disappear as have the moulin kames and crevasse fills immediately east of Kewaskum, on the north side of Highway 28.
The Northern Kettle Interlobate Moraine differs considerably in detail from the Southern Kettle Interlobate Moraine, but their gross chronology and origin have been similar (Alden 1918). The latter would also make a very desirable addition to the Reserve.
Last Updated: 1-Apr-2005