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Systematic Ice Retreat 

in New England

By CARL KOTEFF and FRED PESSL, JR.

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1179

Prepared in cooperation with the New Hampshire 

Department of Resources and Economic Development, 

Connecticut Geological and Natural History Survey, 

Department of Environmental Protection, and 

Commonwealth of Massachusetts Department of Public Works

A discussion of more than 100 years 

of debate on the nature of retreat 

of the late Wisconsinan ice sheet 

from the region

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1981
UNITED STATES DEPARTMENT OF THE INTERIOR 

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY 

Doyle G. Frederick, Acting Director

Library of Congress Cataloging in Publication Data

Koteff, Carl.

Systematic ice retreat in New England.

(Geological Survey professional paper ; 1179) 

Bibliography: p. 

Supt. of Docs, no.: I 19.16:1179

1. Glacial epoch—New England. I. Pessl, Fred, joint author. II. New Hampshire. Dept. of Resources and Economic Development. III. Title. IV. Series: United States. Geological Survey. Professional paper ; 1179. 

QE697.K678 551.7'92'0974 80-607063

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402
CONTENTS

Abstract ________________________________________________ 1

Introduction ______________________________________________ 1

Previous work ______________________________________________ 2

Morphosequence concept ________________________________________ 5

Types of sequences _________________________________________ 6

Physical characteristics of sequences _______________________________ 6

Topographic control of sequences _________________________________ 6

Stagnation-zone retreat _______________________________________ 9

Evidence for a stagnant margin ________________________________ 9

Evidence for the presence of live ice _______________________________ 10

Definition of end moraine __________________________________ 10

Localities of live-ice features _________________________________ 10

Mode of ice retreat _________________________________________ 11

The dirt machine _____________________________________________ 12

Summary _________________________________________________ 15

References cited _____________________________________________ 19

ILLUSTRATIONS

IX*

FIGCKK 1. Diagrammatic profiles of morphosequences _________________________________________________ 7

2. Profiles of four fluvial ice-contact morphosequences in the Pepperell quadrangle, Massachusetts and New Hampshire _____ 8

3. Map of part of the Springfield South quadrangle, Massachusetts and Connecticut, showing downvalley lobation of two retreatal positions of ice ____________________________________________________________ 8

4. Photographs of fault structures in two areas of collapsed glacial-lake sediments, Merrimack, N.H. ________________ 9

5. Photograph of slump features in sediments of glacial Lake Merrimack, Manchester, N.H. ____________________ 10

6. Map showing distribution of Wisconsinan moraines and ice-readvance localities in New England _________________ 11

7. Photograph of till overlying sheared and rotated glacial-lake bottom sediments, Manchester, N.H. ________________ 12

8. Profiles of four successively younger lacustrine ice-contact sequences (kame deltas) in the Clinton quadrangle, Massachusetts- 13

9. Photographs of modern Alaskan glaciers showing debris-rich terminal zones and clean ice upglacier to the firn line _______ 13

10. Photograph showing scree on the Casement Glacier, Glacier Bay National Monument, Alaska __________________ 14

11. Photograph of detached ice block, Casement Glacier ___________________________________________ 14

12. Diagrammatic profile of margin of retreating ice _____________________________________________ 14

13. Photographs showing shear planes containing debris, Casement Glacier ________________________________ 16

14. Photographs showing debris on Casement Glacier derived from shear planes near the area shown in figure 13 __________ 18

15. Photographs of the Casement Glacier showing a thin surface accumulation of morainal debris near the center of the glacier and

debris at the edge of the glacier which is interpreted to be derived chiefly from the "dirt machine" ______________ 18

SYSTEMATIC ICE RETREAT IN NEW ENGLAND

By CARL KOTEFF and FRED PESSL, JR.

ABSTRACT

The mode of ice retreat after the maximum advance of the Wisconsinan glacier that last covered New England has been a subject of 

controversy for more than 100 years. Two major opposing views during most of this period focused on whether recession was characterized 

by systematic retreat of active glacier ice or by regional stagnation. 

Difficulty in correlating with the well-established ice-recessional 

history in the Middle West hampered the discussion in New England. 

In the last few decades, detailed mapping on large-scale topographic 

maps has formed the basis for a third model of deglaciation, the morphosequence concept, which contains parts of both previous views. 

Careful outlining of the distribution and age relationship of melt-water 

deposits shows that the ice sheet receded by a process of stagnationzone retreat and that the region was deglaciated systematically. End 

moraines and readvance localities that demonstrate the presence of 

live ice during retreat in New England are relatively scarce; however, 

the distribution of such localities indicates that live ice was only a few 

kilometers from the margin throughout recession.

The position, volumes, and especially the altitudes of melt-water 

deposits suggest that their source material was debris at or near the 

ice surface. The debris was carried upward from englacial positions to 

the ice surface along shear planes that resulted from live ice moving 

over the obstructing stagnant ice at the glacier margin. Analogous 

shear planes carrying debris have been found in modern valley 

glaciers.

INTRODUCTION

The mode of deglaciation following maximum advance 

of the last ice sheet to cover New England has been a 

matter of controversy for more than 100 years. Opposing views regarding the configuration of the waning ice 

sheet; the condition of the ice, whether active or stagnant; and the rhythm of deglaciation, whether 

systematic and orderly or random and chaotic, have 

repeatedly been argued in the literature. In recent 

years, additional attention has been given to the problem of the sediment source for glacial deposits. Did stagnant ice, cut off from the main active ice mass, contain 

sufficient debris to account for the large volumes of 

glacial sediment present in many parts of New England, 

or do such volumes require a sediment source at the 

margin of the active ice, where it is continually 

replenished by debris from the moving ice mass?

Since the 1940's, U.S. Geological Survey field studies 

have emphasized the detailed delineation of glacial meltwater deposits that establish relative chronologies

within single drainage systems; these studies support 

the concept of systematic northward retreat of an active 

ice sheet fringed by a marginal zone of stagnant ice 

(stagnation-zone retreat). Recently, however, some 

workers have suggested otherwise: that inland from the 

coastal area, where the presence of recessional 

moraines is well established, evidence of ice-margin 

postitions is lacking (Flint and Gebert, 1976); they suggested that large inland areas were characterized by 

regional stagnation during which glacial sediments were 

derived locally from isolated, dead-ice masses (Black and 

Frankel, 1976; Black, 1977). In this paper, we review the 

history of this controversy and attempt to show that the 

nature and distribution of glacial deposits throughout 

most of New England support the concept of systematic 

northward retreat of an active ice sheet and that 

discrete ice-margin positions can be identified.

The conceptual framework now being used by most 

U.S. Geological Survey geologists to study and map 

water-laid glacial deposits in New England is a consequence of changing ideas on the manner in which the 

last continental ice sheet disappeared from New 

England. Early emphasis on "normal retreat," the 

gradual melting back or calving of a well-defined and 

steeply sloping face of live ice, resulted from the natural 

inclination of geologists to interpret New England 

glacial history in light of the midwestern glacial 

stratigraphy, which was based on detailed mapping of 

recessional moraines in the Great Lakes region. As mapping progressed in New England and recessionalmoraine deposits were not readily identified, the inappropriateness of the analogy with the Midwest gradually 

became apparent.

Widespread distribution of ice-contact stratified drift 

throughout much of New England and the apparent 

absence of significant recessional moraines inland from 

the coast led to the concept of regional stagnation, 

where deglaciation resulted in the dissipation of the ice 

as a stagnant mass while at or near its maximum 

southward extension. In this view, downwasting 

thinned the ice sheet to the extent that topographic barriers in areas of high to moderate relief were sufficient 

to induce widespread stagnation.

l
SYSTEMATIC ICE RETREAT IN NEW ENGLAND

These two hypotheses, "normal retreat" and "regional 

stagnation," presented rather opposing views of the 

process of deglaciation, and as often happens, a third 

view evolved somewhere between the two extremes. 

The distribution of ice-contact deposits at the heads of 

graded melt-water deposits, which appeared to be progressively younger northward, suggested that the 

border of the last ice sheet may have retreated as a narrow stagnant zone. This hypothesis of stagnation-zone 

retreat is based on detailed mapping of water-laid 

glacial deposits and brings together the conflicting 

views on the process of deglaciation.

PREVIOUS WORK

During the latter part of the 19th century, mapping of 

glacial deposits in New England had progressed so that 

a prevailing view of the mode of ice retreat could be 

detected in the literature. As a result of his study of 

melt-water deposits in New Hampshire, Upham (1878, 

p. 175) visualized a gradual retreat of the last ice sheet 

at varying rates. Emerson's (1898) map of the glacial 

deposits in old Hampshire County, Mass., shows positions of the ice front, called "ice barriers," and indicates 

that they are progressively younger to the northwest. 

Emerson (1898, p. 563), in his history of the Champlain 

Period, referred to positions of an ice front that in its 

northwestward retreat locally uncovered progressively 

lower spillways and thereby controlled the altitudes of 

extensive proglacial drainages. Similarly, Stone (1899) 

published an isochrone map of Maine showing approximate positions of the ice front based on a tentative correlation of features considered diagnostic of a lobate ice 

front during retreat. Woodworth's (1898, p. Ill) 

research in southern New England indicated that the 

main part of the last ice sheet remained active during 

retreat.

Crosby's (1899, p. 292, 312) study of the late-glacial 

history in the Nashua Valley, Mass., also invoked the 

concept of systematic northward retreat of a distinct ice 

front to explain the history of glacial Lake Nashua and 

its deltaic deposits. However, in a more detailed consideration of the Clinton stage of the glacial lake, he 

(1899, p. 322) noted the scarcity of recessional moraines 

and suggested that stagnation had apparently been 

widespread, perhaps because of strong topographic gradients in the area. Dana (1873, p. 203, 210), in his discussion on the Glacial and Champlain Eras, attributed the 

absence of distinct terminal moraines in New England 

to widespread melting of the glacier surface, instead of 

concentrated melting at the glacier margin. Thus, by the 

end of the 19th century, the majority view seemed to 

favor systematic retreat of an active ice front, but there 

were important dissenting opinions, particularly

regarding the existence, distribution, and significance of 

ice-marginal deposits.

In the early 1900's, many papers appeared in which 

the authors argued in favor of normal retreat in areas of 

eastern and central Massachusetts (Goldthwait, 1905; 

Alden, 1924), New Hampshire (Goldthwait, 1925), and 

central New England (Antevs, 1922). Goldthwait's 

(1905) important early study in the Sudbury Valley, 

Mass., was firmly based on the interpretation of normal 

retreat and systematic uncovering of successively lower 

drainage divides. He concluded that the area had contained a series of proglacial lakes at successively lower 

levels. In a later paper, Goldthwait (1925, p. 33) described the wasting ice sheet in lowland coastal areas of 

eastern New Hampshire and compared the deposition of 

massive ice-marginal ridges there with the great terminal moraine and outwash apron of Long Island, N.Y. 

He (1925, p. 29) described wasting of the ice sheet farther inland, in areas of higher topographic relief, as consisting of "(a) a melting back of its edge at rates usually 

between 200 and 600 feet a year; and (b) a thinning out 

of the sheet by slow downward melting to its surface so 

as to expose the mountain tops and hillsides and leave irregular tongues of ice in the valleys."

Antevs' work in central New England, where he applied De Geer's technique for correlating varved-clay 

layers from one locality to another, was also based on 

the interpretation of systematic northward retreat of an 

active ice front. Antevs' (1922) study, however, involving painstaking measurements of many stratigraphic 

sections in clay pits and natural exposures primarily 

along the Connecticut River, introduced a new approach 

that seemed to identify precise rates of glacier recession, to reconstruct ice-margin positions during each 

year of recession, and to identify stillstands of the ice 

border, even where no recessional moraines were present. J. W. Goldthwait was particulary supportive of 

Antevs' work and noted (in Antevs, 1922, p. ix) that "He 

[Antevs] has worked out successive positions of the 

receding ice border in a region where two generations of 

American geologists, baffled by the absence of definite 

moraines, have realized little or no success."

Although many of the features in central 

Massachusetts that Alden (1924) described as moraines 

are today interpreted as ice-contact heads of outwash 

(Schafer and Hartshorn, 1965, p. 120), his interpretations regarding deglaciation remain of interest. Alden 

(1924, p. 93) stated that the glacier margin melted slowly back from south to north and argued that " * * * the 

ice did not disintegrate throughout the area as a wholly 

stagnant mass, but * * * the retreat of the glacial front 

was effected by a series of stages, with intermittent 

halts and slight marginal accumulations of drift."

However, the early 1900's also had advocates of
PREVIOUS WORK

widespread stagnation: Salisbury and others (1902) in 

New Jersey; Clapp (1904) and Fuller (1904) in 

Massachusetts; and Fuller (1914) and Cook (1924) in 

New York. Clapp (1904, p. 198) concluded from his study 

of glacial Lake Charles, Massachusetts, that the ice 

stagnated many miles back from the ice margin and that 

the dead ice was covered by widespread deposits of sand 

and gravel.

Fuller (1904, p. 181) concluded in his report on studies 

of glacial Lake Neponset in eastern Massachusetts that 

the ice in that region had become completely stagnant 

before the lake formed. He (1904, p. 192) cited the lack 

of moraines and the lack of structures within the 

deposits indicative of forward motion of the ice (that is, 

the absence of folding and faulting) as evidence favoring 

stagnation. Later, Fuller (1914, p. 212) reported that he 

had also found evidence of widespread stagnation in 

Long Island, N.Y., and attributed cessation of glacier 

movement to an ameliorating climate.

Perhaps the most outspoken advocate of widespread 

stagnation at this time was Cook, who reported (1924, p. 

158-159) on the disappearance of the last ice sheet from 

eastern New York:

"As the field work progressed it became evident that 

the region could not be interpreted in accordance with 

the generally accepted theory of the 'retreat' of the 

last continental ice sheet, namely: the gradual melting

back ******* of a fairly definite face of live ice.

"As the inquiry was pushed into various critical 

regions the ice front became more and more fictitious 

and the evidence of wide areas of stagnant ice more 

and more convincing."

Cook also found that recessional ice-marginal features 

were generally absent and that evidence for thick 

masses of stagnant ice was commonly present 

downstream from any inferred position of a retreating 

ice front. He (1924, p. 163) anticipated some of the current work in New England with his remark: "Lacking 

the direct evidence of recessional moraines, some indirect evidence ought to be furnished by an application 

of the ice-front hypothesis to interference with the normal land drainage; there should be found: the records of 

ponded waters with lowering outlets at predictable 

points over cols or across land salients as the assumed 

ice front withdrew."

In 1927, R. F. Flint began his study of the glacial 

geology of Connecticut; later, he published his reports 

summarizing the results of the field studies and setting 

forth the most complete and influential arguments in 

favor of regional stagnation. These papers (Flint, 1929, 

1930), and a subsequent paper (Flint, 1932) in which 

some of the interpretations regarding stagnation were 

revised, had a profound effect on those concerned with

glacial geology in the northeastern United States. 

Flint's eloquent and forceful advocacy of regional 

stagnation dominated the thinking of glacial geologists 

for several decades. In his earlier papers (1929, 1930), 

Flint confronted the longstanding controversy head on, 

albeit from a study area limited primarily to Connecticut. He stated (1930, p. 56): "All of the evidence within 

Connecticut points clearly to the conclusion that when 

the glacier had reached its maximum southward extent, 

it lost its forward thrust and lay stagnant, slowly rotting 

away in place until at length it disappeared. This manner of melting stands in sharp contrast with the slow 

northward retreat of an ice front through Connecticut 

which has hitherto been assigned to the last ice sheet."

Flint (1930, p. 58-59) listed the following objections to 

the concept of normal retreat: 1) the lack of recessional 

moraines; 2) the lack of outwash plains sloping 

southward from the ice front that have ice-contact heads 

sloping to the north; 3) the lack of evidence of active-ice 

deformation in deposits of till or outwash; and 4) the 

presence of untrimmed ice-contact slopes flanking the 

valleys, indicating little or no erosion of older deposits to 

the south by melt water from melting ice to the north. 

Furthermore, he argued (1930, p. 63-64) that field 

evidence was, without exception, consistent with the 

concept of regional stagnation; he noted especially flatlying terraces that had ice-contact slopes facing in all 

directions, indicating that the ice did not recede 

systematically in any one direction but rather shrank 

radially from valley walls.

Taylor (1931), on the other hand, castigated "certain 

geologists" for advocating regional stagnation because 

moraines and other features comparable with those in 

the Great Lakes region were not recognized in New 

York and New England. He wrote (1931, p. 334), 

"Moraines and border drainage features were found in 

abundance, but they are very different from those in the 

West. Nearly all are short fragments, largely terminal 

deposits of narrow ice tongues, with many kames and 

sometimes with banked moraine deposits on the hillside, 

and also with associated marks of border drainage. It is 

difficult in some parts to make out continuous positions 

of alignment of the ice front, but the features show 

oscillating retreat as clearly as they do in the West."

Much of Flint's argument had been stated previously 

by other workers, although the emphasis on a detailed 

field study of terraces and ice-contact deposits was new. 

However, these new elements of the argument were 

challenged most vigorously by some critics and were 

subsequently modified by Flint (1932). Principal among 

these modifications were the identification of southdipping gradients on outwash surfaces that he had 

thought earlier to lie flat and the recognition of erosional 

slopes and scarps where earlier interpretation had
SYSTEMATIC ICE RETREAT IN NEW ENGLAND

indicated primary ice-contact slopes. The 

post-depositional erosional effects of melt water derived 

from ice still existing within a glacial drainage system 

complicated the concept of large-scale regional stagnation, and Flint (1932, p. 156) responded,"* * * a third 

hypothesis * * * that during the deglaciation of 

Connecticut, the ice margin wasted northward, but that 

through an unknown distance inward from the 

periphery, the ice was chiefly stagnant." Unfortunately, 

Flint's modifications of his earlier interpretations and, 

particularly, his sense of a third hypothesis seem to have 

been forgotten. The third hypothesis clearly anticipates 

the idea of stagnation-zone retreat, which at present 

seems best to explain the process of deglaciation in New 

England. However, after publication of Flint's reports 

on the glacial geology of Connecticut, both opponents 

and proponents focused on his earlier interpretations, 

and the controversy continued.

One of the most profound effects of Flint's ideas is 

seen in the reaction of J. W. Goldthwait. Previously, 

Goldthwait (1905, 1925) had worked extensively in New 

England describing proglacial-lake systems, end 

moraines, and readvance localities and, in general, 

documenting evidence for the gradual northward 

retreat of the ice margin. Goldthwait was stimulated by 

Flint's work to reevaluate his interpretation of lateglacial events in New Hampshire. Supplied with more 

detailed topographic base maps, he substantially 

changed his earlier interpretations and completely revised his theory of the way the last ice sheet disappeared. He (1938, p. 371) described, for example, the 

random orientation of ice-contact features and noted 

that"* * * we are not dealing with one continuous ice 

edge that receded in orderly fashion across country, but 

rather with a maze of downwasting, thinning ice which 

lay stagnant or nearly so when these gravels and sands 

finally accumulated, occupying areas so utterly ragged 

in outline and so unstable in pattern that one can hardly 

reconstruct successive stages of ice removal on the 

maps."

In contrast to Goldthwait's ardent support of Flint's 

ideas, Antevs (1939) took strong exception to them. He 

(1939, p. 506-507) envisioned a distinct, gently to steeply sloping ice margin characterized by wastage at the ice 

border due primarily to melting and evaporation, and he 

thought that interior ablation (evaporation and 

outflowage) had resulted in a lowered ice surface. 

Antevs (1939) acknowledged the existence of a marginal 

belt of stagnant ice but noted that it probably occupied 

only a part of the zone of melting; he (1939, p. 507) further emphasized that "The fact that a belt of dead-ice 

topography may be 25 or more miles wide does not imply 

that there was so broad a belt of stagnant ice at any one 

time."

Reporting on his studies in the Housatonic Valley, 

western Massachusetts, Logan (1938, p. 55) also argued 

in favor of an active ice sheet during recession but noted 

that ice-margin deposits such as kames and heads of outwash were discontinuous in areas of high topographic 

relief and that correlation of these deposits was difficult. 

He envisioned a very irregular ice margin consisting of 

long narrow lobes extending downvalley.

In 1934, Flint's study of the Quinnipiac-Farmington 

lowland in Connecticut was published; in it, the author 

described ice-contact deposits, varved clay, and 

postglacial terrace deposits in the context of widespread 

stagnation. Lougee in 1938 reported on his study of the 

same area and offered an alternative interpretation of 

late-glacial events in which systematic northward 

retreat of the ice controlled the formation of a series of 

proglacial lakes and the sequence of deposition of fluvial 

gravels. In 1940, Lougee published "Deglaciation of 

New England" in which he contradicted many of the 

reinterpretations of features in New Hampshire offered 

by J. W. Goldthwait (1938) in support of stagnation and 

downwasting. Lougee (1940, p. 191-192) defended 

Antevs' varve chronology, particularly in northern New 

England, and cited Antevs' (1922) study as 

demonstrating progressive northward retreat of the ice 

sheet. Lougee acknowledged that recessional moraines 

as evidence of active ice were notably scarce in New 

England and suggested that the rugged topography and 

rapid rates of retreat were possible reasons. However, 

he was unwilling to discount several reported moraines 

that Goldthwait, in his reinterpretation (1938, p. 

348-352), had discredited. Lougee (1940, p. 193-194) 

acknowledged that some earlier interpretations of 

localities attributed to active ice deformation and 

deposition merited revision, for example, the AmherstNorthampton evidence in Massachusetts and the Claremont "readvance" in New Hampshire. However, Lougee 

(1940, p. 195) maintained that other localities such as the 

Littleton-Bethlehem, N.H., moraine system and 

associated exposures showing till sheets separated by 

stratified deposits remained firm testimony to the 

presence of active ice during retreat. In addition, 

Lougee interpreted ice-contact stratified sediments 

alined northwest in the coastal region of New Hampshire as deposits of glacial melt water issuing from the 

ice margin and flowing at right angles to the retreating 

ice front. Goldthwait considered these deposits as 

resulting chiefly from deposition in irregular pools and 

broad channels produced by the uneven downwasting of 

the glacier surface. Other deposits such as pitted coastal 

clays, interior-valley outwash, and the widespread icecontact sediments in the White Mountains also were interpreted differently by Lougee and Goldthwait 

(Lougee, 1940, p. 199-213).
MORPHOSEQUENCE CONCEPT

Douglas Johnson (1941) attempted to clarify a problem that he considered to result largely from semantic 

difficulties related to the longstanding controversy. He 

emphasized that "retreat" refers only to the position of 

the ice margin and that "downwasting" refers only to 

the ice mass, never to the position of the margin. 

Johnson (1941, p. 85-90) also pointed out (1) that the 

presence or absence of recessional moraines depends on 

the interaction of several variables: topographic relief, 

rate of glacier flow, rate of ice wastage, and sediment 

source; and (2) that the absence of recessional moraines 

does not mean that the ice margin was not retreating, 

but rather that retreat was too continuous for moraines 

to form.

Unfortunately, Johnson's arguments depended to 

some extent on an oversimplified comparison of conditions on an alpine glacier with those on a continental ice 

sheet. He also tended to discount the distinctive nature 

of ice-contact deposits (Woodworth, 1899; Thwaites, 

1926; Flint, 1928) and their importance as indicators of 

stagnant-ice conditions, thus rejecting an important 

field criterion for identifying distribution and nature of 

the local ice regimen. Johnson acknowledged that the 

debris-laden margin of a wasting continental glacier is 

likely to produce isolated masses of stagnant ice, but he 

(1941, p. 94) considered defining the former extent of 

such masses in New England an unreasonable prospect. 

Johnson (1941) recalled an argument by Antevs (1939, p. 

507) that "A zone of stagnant ice one hundred miles 

broad, and a zone of stagnant ice a mile broad receding 

with the ice margin over a belt one hundred miles broad, 

may leave fluvio-glacial phenomena of like character." 

Johnson concluded (1941, p. 94), "Whether the two 

histories can be discriminated from examination of the 

residual deposits and forms must remain in doubt until 

highly critical studies have been made."

In recent decades, detailed mapping on large-scale 

topographic bases (most at 1:24,000 scale and most having 10-ft (3-m) contour intervals) has been completed for 

extensive areas in Massachusetts, Rhode Island, Connecticut, and New Hampshire. In addition, several 

notable discussion papers have been published in which 

the authors presented new ideas on the question of 

deglaciation in New England (Jahns, 1941, 1953; 

Currier, 1941; Rich, 1943; White, 1947; Schafer, 1961; 

Schafer and Hartshorn, 1965; Koteff, 1974). It now 

seems reasonable to suggest that since the early 1940's, 

just such "highly critical studies," as envisioned by 

Johnson (1941, p. 94), have been made in southern and 

central New England, that the cumulative results of this 

work do permit definition of a stagnant zone that 

migrated northward during deglaciation, and that a 

plausible model of deglaciation, incorporating elements

of both normal retreat and downwasting accompanied 

by stagnation, has evolved.

This model, now called the morphosequence concept, 

was first advanced by R. H. Jahns (1941, 1953), on the 

basis of field studies in north-central Massachusetts. His 

work was plotted on newly introduced, accurate, 

7V2-min topographic maps at a scale of 1:31,680, having 

a 10-ft (3-m) contour interval. These maps allowed Jahns 

to make a very detailed analysis of the morphology, texture, and distribution of melt-water deposits. The importance of the introduction of these new maps in the early 

1940's cannot be overemphasized because they provided 

a source of data previously unavailable to protagonists 

of either normal retreat or regional stagnation. The enthusiasm of glacial geologists regarding the 

l:31,680-scale maps matched that of J. W. Goldthwait in 

1905 regarding the then-new 15-min topographic maps 

for the Concord, Mass., area, where he thought orderly 

retreat of the ice sheet was well demonstrated. Ironically, when he later began to favor regional stagnation, he 

(1938, p. 346) mentioned, " * * * complete contour mapping of New Hampshire * * * " on a 15-min base had 

"afforded better opportunity to judge the relative importance of downward and backward melting of the ice."

MORPHOSEQUENCE CONCEPT

Since Jahns introduced the sequence concept in 1941, 

some confusion has existed about what sequences are 

because the word "sequence" has a connotation of time 

that was not originally intended. In the concept, a single 

sequence specifically refers to a continuum of landforms 

composed of melt-water deposits, from more collapsed 

forms due to melting of ice blocks at the head or 

upstream parts of outwash, to progressively less collapsed forms downstream. A sequence can thus be 

viewed as a body of stratified drift laid down, layer upon 

layer, by melt water at and beyond the margin of a 

glacier, while deposition was controlled by a specific 

base level. The complexity of the morphologic features 

depends on the relative number, size, and distribution of 

detached ice blocks around and over which the sequence 

was deposited. For example, at the head of outwash 

near or at the ice margin, a sequence may be composed 

of typical ice-contact features, such as ice-channel fillings and kames, which show a considerable amount of 

collapse; downstream, the less collapsed forms may be 

kame terraces or kame plains, and beyond any area of 

residual ice blocks, the form may be an outwash plain. 

All the forms in this continuum are regarded as part of 

one time unit and, thus, the word sequence in this sense 

does not refer to a span of time but to a progression of 

more collapsed to less collapsed contemporaneous 

forms. One individual sequence has a time significance
SYSTEMATIC ICE RETREAT IN NEW ENGLAND

only in relation to other sequences. Although another 

word originally may have been more desirable to avoid 

confusion, the term "sequence(s)" has been established 

too long in the literature on New England glacial 

deposits to be abandoned completely.

In an effort to clear up some of the confusion and still 

retain the term "sequence," Koteff (1974) introduced the 

term "morphologic sequence." Since then, W. C. 

Mahaney (1976) has suggested a term that we think is 

even more suitable. Mahaney (1976, p. vi) referred to J. 

H. Hartshorn's description1 of New England melt-water 

deposits as " * * * morphosequences of time-equivalent 

groups of landforms." Mahaney's objection (written 

communication, 1979) that the term "morphologic sequence" is too closely related to terminology used by 

pedologists to indicate changes in soil configuration with 

time, appears to us to be well taken. Thus, we hereby endorse the term "morphosequence" to describe the concept originally introduced by Jahns in 1941. In this 

paper, morphosequence and sequence are used interchangeably.

TYPES OF SEQUENCES

The first application of the sequence concept to meltwater deposits by Jahns (1941) dealt primarily with 

fluvial sediments, but the model now includes lacustrine 

and marine deposits as well, and eight major types of 

morphosequences are presently identified (Koteff, 1974). 

Types of sequences are distinguished (fig. 1) on the basis 

of whether they were deposited in a fluvial, lacustrine, 

or marine environment, of whether they were in contact 

with the stagnant-ice margin, and of whether they had 

an associated end moraine.

PHYSICAL CHARACTERISTICS OF SEQUENCES

Textural distribution.—Each morphosequence is 

much like any water-laid unit, in that the texture at the 

surface of the deposits is coarser near the head of outwash or source and becomes finer grained downstream. 

The textural boundaries are not always sharp or easily 

distinguished; locally, within any given morphosequence, gravel can be found in an area of finer textures, or sand can be found in an area of gravel. Also, 

very short sequences show little textural change from 

one end to the other; some have only gravel at the surface and some have only sand, depending on the nature 

of the source material and, perhaps more importantly, 

on the depositional gradient. However, textural gradation downstream from the headward source area is 

generally persistent for the entire length of most 

sequences.

1 J. H. Hartshorn, address to the Conference on Quaternary Stratigraphy of North America 

at York University, Downsview, Ontario, Canada, 1975.

Base-level controls.—The determination of a base-level 

control for deposition is as important in distinguishing 

one morphosequence from another as is locating the 

origin or head of outwash of sequences. Base-level controls include spillways underlain by bedrock or till, 

previously deposited masses of sand and gravel (mostly 

older sequences), standing-water bodies such as glacial 

lakes (which in turn were controlled by a separate 

spillway) or even the sea, and stagnant-ice masses. Live 

ice has not been identified as having acted as a base-level 

control in New England. Spillways underlain by bedrock 

clearly were the most durable, whereas those underlain 

by glacial drift were more subject to varying degrees of 

erosion. However, some spillways underlain by sand and 

gravel appear to have lasted for a significant time; for 

example, the one that presumably was the outlet for a 

glacial lake in Cape Cod Bay (Oldale, 1974) was used 

during the time several consecutive sequences were constructed. Factors that may have contributed to such 

durable spillways in sand and gravel are the possible 

presence of ice-cored drift and a very shallow 

downstream gradient that may have retarded headward 

erosion of the spillway.

Profiles.—Topographic profiles drawn in a general 

downstream direction can aid in distinguishing one morphosequence from another. Figure 2 shows profiles of 

four successively younger fluvial ice-contact sequences 

near Dunstable, Mass. (Pepperell quadrangle, 

Mass.-N.H.) The profiles were constructed by projecting 

at right angles to an approximated longitudinal 

centerline maximum altitudes of deposits within approximately 600 m on either side of the centerline. This 

method produces a reasonable representation of the 

precollapse surface by smoothing out the irregularities 

in deposits where adjacent or buried ice blocks melted 

out, as well as irregularities caused by postdepositional 

erosion. The idealized gradients shown in figure 2 are 

straight-line segments, which appear to be most common for sequences mapped in New England, although 

upward curving of the profile near the heads of outwash 

is found in many deposits where collapse has not been 

too extensive. Profiles are very helpful in indicating the 

relative ages between sequences within a single 

drainage system, especially when used with textural 

data that show the relative downstream gradation of 

coarse to fine clast sizes.

TOPOGRAPHIC CONTROL OF SEQUENCES

The distribution, position, and shape of morphosequences were closely controlled during their deposition by the topography of New England, an important 

factor in unravelling the chronology of ice retreat in the 

region. Local relief appears to have had a close relationship with ice thickness, as reflected in the amount of
MORPHOSEQUENCE CONCEPT

AREA OF DEBRIS 

ACCUMULATION

DETACHED ICE BLOCKS BASE-LEVEL 

CONTROL

TILL'; QR:: BEDROCK.::

D AREA OF DEBRIS 

ACCUMULATION

AREA OF DEBRIS 

ACCUMULATION

AREA OF DEBRIS 

ACCUMULATION

SPILLWAY 

LAKE LEVEL |

AREA OF DEBRIS 

ACCUMULATION

DETACHED 

ICE BLOCK

AREA OF DEBRIS 

ACCUMULATION

LAKE SPILLWAY-FLUVIAL 

BASE-LEVEL CONTROL

B'OTTO'MSETf 'iEDS

FIGURE 1. Diagrammatic profiles of morphosequences (Koteff, 1974, p. 128-129). Detached 

ice blocks and stagnant ice masses are sites of future collapsed ice-contact slopes. A, Fluvial 

ice-contact sequence. B, Fluvial non-ice-contact sequence. C, Lacustrine ice-contact sequence. D, Fluvial-lacustrine ice-contact sequence. E, Fluvial-lacustrine non-ice-contact sequence. F, Lacustrine-fluvial ice-contact sequence. Not shown are sequences representing a 

marine environment and sequences associated with an end moraine.
SYSTEMATIC ICE RETREAT IN NEW ENGLAND

Vertical exaggeration x 20

2 MILES

3 KILOMETERS

FIGURE 2.—Profiles of four fluvial ice-contact morphosequences in the Pepperell quadrangle, Massachusetts and New Hampshire. Sequence 1 

is the oldest. Solid-line tangents indicate an idealized gradient for the sequences; base-level controls are south and east of the area. Dashed 

lines represent successive positions of the stagnant ice front; numbers refer to related sequences. Modified from Koteff and Volckmann 

(1973).

lobation at the ice margin, particularly in the larger 

valleys. For example, stagnant-zone deposits and a later 

morphosequence near Springfield, Mass. (fig. 3), outline 

two positions of a lobe that extended about 8 km 

downvalley. The Connecticut Valley in this area has a 

relief of about 275 m, a width of about 24 km, and a 

regional slope of less than 1 m/km. Langer (1977) has 

demonstrated that ice recession farther south in the 

Connecticut Valley near Glastonbury, Conn., was 

simultaneous both upvalley and away from the valley 

walls. As the retreating stagnant-ice margin uncovered 

lower and lower outlets along the eastern valley border, 

correspondingly lower morphosequences were 

deposited; these deposits parallel the major structural 

and topographic northeast trend of the valley wall. 

Other valleys in New England of lesser relief and width 

show correspondingly less lobation of the ice margin. 

During retreat of the ice in the southern Merrimack 

Valley in New Hampshire, for example, the ice margin 

was lobate downvalley for about 2.5 km; the valley in 

this area is about 8 km wide and has a regional slope of 

less than 1 m/km.

Topographic control of the distribution and position of 

morphosequences cannot be demonstrated for all areas 

in New England because many upland areas contain no 

melt-water deposits at all. However, wherever morphosequences are found throughout New England, even 

slight topographic irregularities have influenced their 

shape, position, and distribution by providing temporary 

basins and outlets or base-level controls for melt water. 

There are some notable examples in which melt-water 

deposits themselves dammed valleys; for example, the 

drift dam for glacial Lake Hitchcock at Rocky Hill, 

Conn. (Flint, 1933, p. 977-978; Jahns and Willard, 1942, 

p. 281). The dams created depositional basins and 

outlets for later sedimentation, but the positions of 

these drift dams were controlled by the local 

topography.

42°05'-

42°00'

72°35' 72°30'

Stagnant-ice 

margin 1

Stagnant-ice 

margin 2

2 MILES

\

3 KILOMETERS

EXPLANATION

Sz Stagnant zone

melt-water deposits 

Row lines of fluvial

lacustrine deposits

FIGURE 3.—Part of the Springfield South quadrangle, Massachusetts 

and Connecticut, showing downvalley lobation of two retreatal positions of ice. Stagnant-zone deposits were laid down entirely within 

the stagnant margin during the earlier and more southerly retreatal 

ice position. Modified from Hartshorn and Koteff (1967).
STAGNATION-ZONE RETREAT

STAGNATION-ZONE RETREAT 

EVIDENCE FOR A STAGNANT MARGIN

The most conspicuous features that mark retreatal ice 

positions in New England are the heads of outwash of 

fluvial or lacustrine ice-contact melt-water deposits. 

Most of the deformation structures exposed in nearly all 

the ice-contact heads in scores of mapped morphosequences resulted essentially from collapse due to 

melting of adjacent or buried motionless ice. The only 

ice-contact heads of outwash that indicate the presence 

of live ice are those associated with end moraines, which 

are very scarce except in the coastal areas of New 

England. The collapse structures include normal faults, 

high-angle reverse faults, slumps, and debris flows. In 

some graben structures, the upper parts of the fault 

planes curve over the downdropped blocks and become 

reverse faults (fig. 4). In some exposures, only the upper 

curved parts of such faults are exposed, giving an appearance of overthrusting that possibly could be confused with ice shove. However, the collapse origin of 

these types of structures becomes clear for the most 

part at depth. McDonald and Shilts (1975) described 

many such normal and reverse faults resulting from collapse due to melting ice in glaciofluvial sediments. Stone 

(1976) described extraordinarily complex slump features 

(fig. 5) caused by melting of ice in glacial-lake sediments. 

These are just a few examples of faults and slumps that 

demonstrate the prevailing style of deformation 

throughout the region: this style of deformation strongly indicates that the ice margin was stagnant where it 

was in contact with morphosequences in a variety of 

depositional environments.

FIGURE 4.—Fault structures in two areas of collapsed glacial-lake sediments, Merrimack, N. H.; the collapse resulted from melting of 

buried ice. A, Curve of faults becomes less toward the center of collapse to the left. B, Downdropped sediments are to the right of the 

curving fault.

The heads of outwash of sequences laid down beyond 

the ice margin contain either few or no collapse 

features, depending on the relative abundance of stray, 

detached, ice blocks. No evidence of ice-shove or live-ice 

structures has been found either in the upstream areas 

of such sequences or at the presumed ice margin from 

which these deposits originated.

Although most morphosequences were laid down at 

and beyond the edge of the stagnant margin of the 

glacier, water-laid bodies deposited completely within 

the stagnant-ice zone are present in many places. The 

stagnation-zone deposits near Springfield, Mass. (fig.3), 

for example, contain sand, gravel, and flowtill that show 

only collapse structures. These and other similar 

deposits appear to represent sedimentation entirely 

within, and having a base level controlled by, stagnant 

ice. In contrast, most morphosequences have headward 

parts that were laid down within the stagnant zone, but 

had base levels beyond the ice edge, suggesting that

*v

~»«us^vJJjJi/'-»?»fe

ffs^^IP^^-*^*"

-3U*f!a. . _***£ l«rf8S
10

FIGURE 5.—Slump features in sediments of glacial Lake Merrimack, 

Manchester, N. H. Folding and shearing probably were caused by 

melting of buried ice to the left of the section. Note later undisturbed 

sediments over slumped features. Photograph by Byron D. Stone.

most melt-water drainage within the stagnant zone was 

integrated with that of the ice-free proglacial areas.

EVIDENCE FOR THE PRESENCE OF LIVE ICE

DEFINITION OF END MORAINE

The terms "moraine" and "end moraine" often have 

been used ambiguously to describe various features in 

New England that were constructed at the edge of an 

ice sheet. This ambiguity has hampered discussions on 

the regimen of the ice sheet during recession. For example, the term "kame moraine" has been applied to 

deposits in southeastern Massachusetts that no doubt 

were laid down entirely within the stagnant zone. As 

mentioned above, Alden (1924) used the word "moraine" 

to describe what are now viewed as ice-contact meltwater deposits. Large bodies of melt-water deposits in 

the St. Lawrence Valley in Canada and in the Finger 

Lakes region in New York are referred to as moraines. 

Although these are very striking features, large parts of 

them appear to be parts of one or another type of morphosequence.

On the other hand, the word "moraine" has been more 

properly used in describing features associated with or 

built at the edge of live ice in many places. Therefore, 

within the conceptual framework of the morphosequence model and stagnation-zone retreat, it seems 

more appropriate that the terms "moraine" and "end 

moraine" be applied only to features that were constructed, at least in part, by live ice, so as to distinguish 

them from morphosequences and stagnant-zone meltwater deposits. Such a distinction is important because 

knowledge of the distribution of live ice relative to the 

stagnant margin during ice retreat helps us to understand the glacier regimen.

SYSTEMATIC ICE RETREAT IN NEW ENGLAND

LOCALITIES OF LIVE-ICE FEATURES

Although the physical characteristics and positions of 

most melt-water deposits in New England suggest that 

a predominantly stagnant marginal zone was part of the 

receding ice sheet, a few localities inland from the 

coastal areas indicate that live ice either constructed 

end moraines or readvanced over melt-water deposits at 

various times during general ice recession. The bulk of 

the well-known morainal system that stretches from 

Long Island, N.Y., to Cape Cod, Mass. (fig. 6), appears 

to have been formed near the maximum extent of the 

glacier, which roughly coincides with the coastal areas 

of southern New England. Even on this large scale, 

topographic control of ice lobation and related deposits 

is very evident; the pronounced eastward lobation of the 

morainal belt was due to the successively deeper 

topographic basins in that direction. Well-defined 

moraines also have been identified parallel to and along 

the coast of Maine (Borns, 1968). Inland from the coast, 

the few known end moraines (fig. 6) include the Fresh 

Pond moraine (Chute, 1959) near Boston, a small end 

moraine near Hardwick, Mass., and a very short, segment of a probable end moraine near South Coventry, 

Conn. The South Coventry feature has been interpreted 

as a melt-water deposit laid down in a system of 

regionally stagnating ice (Black and Frankel, 1976; 

Black, 1977), but the presence of till and the morphology 

of the ridge there suggest that it is rather a moraine constructed at least in part by live ice. Thompson (1976) 

described some hitherto unknown moraines inland from 

coastal Maine in Kennebec County.

Readvance localities (fig. 6) not associated with end 

moraines include the Middletown readvance in the Connecticut River valley (Flint, 1953), a readvance near Mt. 

Tom, Mass. (Larsen, 1972), and a minor readvance near 

Manchester, N.H. (Stone and Koteff, 1979). The Manchester locality shows till overlying sheared and deformed lake-bottom sediments (fig. 7) and is interpreted 

as a minor local pulse of the ice sheet over deposits of 

glacial Lake Merrimack, which occupied south-central 

New Hampshire during the general retreat of the last 

glacier. Lougee (1935) described a readvance farther 

north, near East Barnet, Vt., over varved clays 

deposited in glacial Lake Hitchcock. Connally (1970) 

demonstrated that to the west, ice readvanced near 

Bridport,Vt. Bloom (1960) reported a readvance over 

marine sediments along the southwest coast of Maine.

These localities are most of the known, welldocumented examples of end moraines and ice readvances. Other possible readvance localities in New 

Hampshire were recorded by Upham (1878) and Crosby 

(1934), but were later dismissed by Goldthwait (1938). 

Whether these localities are actual readvance sites,
STAGNATION-ZONE RETREAT 11

FIGURE 6.—Distribution of Wisconsinan moraines and ice-readvance localities in New England, B, Bridport readvance; BBM, Buzzards Bay 

moraine; CM, Charlestown moraine; C-MM, Cherryfield to Machias moraines; EB, East Barnet readvance; EM, Ellisville moraine; FPM, 

Fresh Pond moraine; GQM, Great Quittacas Pond moraine; HHM, Harbor Hill moraine; HM, Hardwick moraine; KM, Kennebec moraines; 

KK, Kennebunk readvance; LM, Ledyard moraine; MA, Manchester readvance; MI, Middletown readvance; MT, Mount Tom readvance; NM, 

Nantucket moraine; PJM, Point Judith moraine; RM, Ronkonkoma moraine; SCM, South Coventry moraine; SM, Sandwich moraine. 

Moraines on Long Island and along southern New England coast modified from Schafer and Hartshorn (1965).
12 SYSTEMATIC ICE RETREAT IN NEW ENGLAND

FIGURE 7.—Till overlying sheared and rotated glacial-lake bottom 

sediments, Manchester, N.H. Relative movement from right to left. 

Photograph by Grahame J. Larson.

therefore, remains in doubt. Although, almost assuredly, other places in New England show evidence of an active edge to the retreating Laurentide ice sheet, the 

relative scarcity of such localities is apparent 

throughout New England. All the well documented inland recessional moraines and readvance localities are 

interpreted as strictly local features. That is, the 

distance covered by any single readvance, although not 

precisely known, is probably not more than a few 

kilometers (Larsen, 1972; Stone and Koteff, 1979). In a 

regionally stagnating system, however, a very large 

area of ice (of regional proportions) would have to be 

reactivated for each readvance; each readvance would 

be followed by an interlude of stagnation. The 

widespread distribution of the known localities, scarce 

as they are, and the apparent short distances involved in 

the ice readvances indicate that live ice was never far 

from the stagnant margin during deglaciation.

MODE OF ICE RETREAT

Morphosequences have been recognized and mapped 

in many parts of southern, central, and northern New 

England, in large and small depositional basins, as well 

as in many upland areas. Because of the relative scarcity 

of live-ice features such as end moraines and readvance 

localities away from the coast, the only indicators of 

retreatal ice-margin positions in most of the region are 

the outwash heads of the sequences themselves. The 

abundance of morphosequences and the scarcity of 

localities that demonstrate a live-ice edge suggest that a 

zone of stagnant ice bordered the live ice of the continental glacier and acted as a buffer between the active 

ice and melt-water deposits. This model is called 

"stagnation-zone retreat" (Currier, 1941).

The width of the stagnant zone is not well known, but 

can be estimated from the length of eskers or icechannel fillings that served as feeders to melt-water 

deposits within a single sequence. In New England, all 

ice-channel fillings, some of which are as much as 2.5 km 

long (Koteff, 1974), show collapse structures indicative 

of contact with stagnant ice. However wide the stagnant 

zone was, it appears to have been a persistent feature of 

the receding ice sheet in the region.

The careful study of hundreds of morphosequences in 

scores of inland quadrangles within southern New 

England demonstrates a systematic and chronologic 

relationship among sequences; this relationship, in turn, 

indicates that the northward retreat of the last ice sheet 

was systematic and was interrupted by only a few 

pauses or small readvances at scattered localities 

throughout the region. This systematic relationship is illustrated by the shingled profiles of sequences in 

drainage areas such as those shown in figure 2; it is 

perhaps even better illustrated by the shingled profiles 

of deltas in glacial lakes, particularly of deltas deposited 

in glacial lakes that were maintained at the same level 

for a considerable time. For example, figure 8 outlines 

profiles of several successive deltas laid down during the 

Clinton stage of glacial Lake Nashua in north-central 

Massachusetts. This lake was held at the same level by a 

bedrock spillway for the amount of time it took for the 

ice margin to recede north more than 13 km. The topset 

fluvial part of each of these deltas shows a general textural gradation of relatively coarser clast sizes at the icemarginal head to finer downstream. The combination of 

a persistent lake with several deltas of melt-water 

deposits that are graded to a constant water level, that 

show en echelon or shingled profiles, and that have 

coarse clasts upstream and smaller particles 

downstream can best be explained by systematic ice 

retreat.

THE DIRT MACHINE

In previous discussions on whether deglaciation in 

New England was accomplished by regional stagnation 

or systematic ice retreat, little attention was given to 

the source of debris washed out of glacier ice by meltwater streams. However, ideas on the source of this 

sediment, whether from stagnant ice or from actively 

flowing ice, are closely related to ideas concerning the 

mode of ice retreat. The morphosequence concept has 

led to a view of debris origin that favors systematic ice 

retreat rather than regional stagnation.

Regional stagnation requires that the motionless ice, 

covering vast areas, contained enough material to supply the large amounts of sediment deposited by meltwater streams during general ice wastage. Much of the
THE DIRT MACHINE 13

METERS

125 —i Foreshortened 

about 1.5 km

100-

75-

2 MILES 

J

3 KILOMETERS

FIGURE 8.—Profiles of four successively younger lacustrine ice-contact sequences (kame deltas) in the Clinton quadrangle, Mass. Sequence 1 is 

the oldest. Solid triangle represents bedrock spillway. Dashed lines indicate approximate edges of stagnant ice. Modified from Koteff (1966).

FiGi'KK 9.—Debris-rich terminal zones and clean ice upglacier to the firn line in modern glaciers. A, Tebenkof Glacier near Whittier, Alaska. B, 

From left to right, Scott Glacier, Sheridan Glacier, and Sherman Glacier near Cordova, Alaska. Wide area of debris covering on Sherman 

Glacier snout resulted from landslide during earthquake of March 27, 1964 (Shreve, 1966). Photographs taken August 1975.

material would have had to be distributed in englacial or 

superglacial positions to account for the present positions and altitudes of melt-water deposits. Most studies 

of debris transport by glaciers, however, indicate that 

the bulk of material is carried at the base or in the lower 

few meters of ice sheets (Goldthwait, 1971; Boulton, 

Dent, and Morris, 1974; Boulton, 1975). Present valley 

glaciers (for example, in Alaska) also seem to be extremely dirty or debris laden only at their snouts (fig. 9). 

If any of these valley glaciers, and, by analogy, continental glaciers, were suddenly to stagnate and dissipate, the 

major debris source would be in the basal parts and at 

the snout or edge, but not in any other part of the 

glacier. The altitude, position, and volume of morphosequences in New England suggest that regional 

stagnation is unlikely to have supplied the debris 

necessary to account for their systematic and 

widespread distribution. Many thick morphosequences 

are found all across the area and not just at the 

hypothetical edge of a regionally stagnating ice sheet.

Superglacial debris such as scree or other material 

derived by mass movement from adjacent valley walls is 

found locally on the surface of most present-day alpine 

glaciers (fig. 10), and debris produced by similar processes can be considered as a possible source for outwash 

deposits from a regionally stagnating glacier. In many 

areas of New England, however, the altitude of morphosequences and the large sediment volume within 

them are not consistent with this concept. For example, 

most of the preglacial landscape of southeastern 

Massachusetts and of many parts of Rhode Island is 

completely overwhelmed by water-laid deposits whose 

lithologic composition strongly reflects the local 

bedrock. These deposits are at altitudes much greater 

than those of the highest local bedrock; thus, there was 

no high source area from which rock debris could move 

down onto the surface of the ice and subsequently be 

washed out by streams. Furthermore, the volumes of 

water-laid drift in New England appear to be much 

larger than volumes that could have come from such
14 SYSTEMATIC ICE RETREAT IN NEW ENGLAND

FIGURE 10.—Scree on the Casement Glacier, Glacier Bay National 

Monument, Alaska. Figure in center of picture indicates scale. 

Photograph taken July 1975.

surface debris, even where it may have accumulated 

locally. Scree on the surface of some existing valley 

glaciers has an imposing appearance, but is only a very 

thin surface layer where present (fig. 11) and, therefore, 

seems a very unlikely source of large amounts of debris. 

A process that appears to account for the large 

volumes of material that compose morphosequences and 

that is compatible with the systematic distribution of sequences is one in which the live ice continuously moves 

forward and is sheared up against the motionless 

marginal belt of the stagnant zone (fig. 12). Thinning of 

the ice sheet at the edge accompanying general recession results either in marginal ice no longer thick 

enough to support forward motion or in a significantly 

reduced rate of motion in this zone. The marginal ice 

then becomes an obstruction to the faster moving ice

Area of active debris 

accumulation (see 

figures 13 and 14)

FIGURE 11.—Detached ice block, Casement Glacier, showing only thin 

surface covering of debris. Sides of the block have been partly 

covered by mud flowing from the ice surface during melting. 

Photograph taken July 1975.

behind it, forcing the upward shearing of the live ice, 

and tending to further promote stagnation of the slower 

moving ice. Abraded material transported at the base of 

the ice is carried upward toward the surface along these 

shear planes.

During continuous retreat, the zone of active shearing 

migrates up ice, leaving behind debris-laden relict shear 

planes in the stagnant zone. As the ice melts, the debris 

in the relict shear planes is concentrated at the stagnant 

margin. Melt-water streams, principally from the surface of the live ice, pass through the concentration of 

debris, picking up material and depositing it in, and 

mostly beyond, the stagnant zone as morphosequences. 

Pebble lithologies indicate that most outwash clasts in 

New England were transported no more than a few 

kilometers from the bedrock source. Thus, the zone of

Stagnant ice (stagnant zone)

Bedrock or older drift

FIGURE 12.—Diagrammatic profile of margin of retreating ice. Solid lines (arrows) indicate shear planes along the live-ice/stagnant-ice interface; 

dashed lines in the stagnant zone indicate relict shear planes of former live-ice/stagnant-ice interfaces.
SUMMARY 15

maximum ice abrasion probably was not very far from 

the margin of the glacier throughout deglaciation. 

Whatever debris that was not reworked and carried out 

beyond the stagnant zone by fluvial action probably 

ended up mostly as ablation till, let down as the motionless ice melted away. Very qualitative observations 

indicate that most of the surface till in New England 

was transported no more than about 1.5 km from its 

bedrock source. This small transport distance also suggests that the zone of maximum abrasion was near the 

edge of the live ice.

The extreme angularity of scree, such as that found on 

the Casement Glacier (fig. 10), also appears to preclude 

scree as a significant source of material. Although scattered local postglacial talus accumulations have very 

angluar clasts, very few of the boulders and stones of 

the till landscape of New England, including all areas of 

superglacial till, approach the degree of angularity 

found in modern analogs such as the Casement Glacier.

Features interpreted to be shear planes were found 

near the distal parts of the Casement Glacier in 1975, 

slightly up ice from the stagnant margin (figs. 13 and 

14). The shear planes contain boulder-size to silt-size 

clasts. The roundness of the clasts in these shear planes, 

which may have resulted from abrasive transport at the 

base of the glacier, is much greater than that of clasts in 

the scree shown in figure 10, which is merely riding 

along on the glacier surface. No quantitative data are 

available on the amounts of material that could have 

been brought up along such shear planes; however, we 

do see that only the distal part of the Casement Glacier 

(fig. 15) contains appreciable debris.

The idea that debris is carried upward along shear 

planes at the live-ice/stagnant-ice interface of a glacier 

is certainly not new, and we think it readily explains 

present altitudes and thicknesses of morphosequences 

found in New England where no higher source now exists. The continuous process of forward-moving ice supplying debris for redistribution by melt-water streams 

also appears to explain the enormous volumes of sand, 

gravel, silt, and clay now found in sequences throughout 

New England. The live ice acting as a conveyor belt, 

constantly delivering material to the stagnant zone, has 

been referred to as the "dirt machine" (Koteff, 1974).

SUMMARY

The long-standing controversy over the nature of 

recession of the last ice sheet to overrun New England, 

whether by regional stagnation or "normal" retreat, 

became more sharply focused by the work of R. H. Jahns 

in the early 1940's. This work, on newly introduced, 

detailed topographic base maps, and later studies, chiefly by members of the U.S. Geological Survey, began to 

shift the weight of the argument toward the view of normal retreat, at the same time incorporating some 

aspects of regional stagnation such as the presence of a 

stagnant zone at the margin of a systematically receding 

ice sheet. The model, now called the morphosequence 

concept, demonstrates the presence of numerous 

retreatal ice-margin positions. The importance of 

topographic control of the distribution of melt-water 

sediments is emphasized, rather than the effects of 

climatically controlled stillstands of the continental 

glacier. Furthermore, the distribution, altitude, and 

volume of melt-water deposits strongly suggest that live 

ice delivered abraded material from below, up along 

shear planes at the live-ice/stagnant-ice interface, as a 

continuous process during retreat. Direct melting out of 

rock debris from stagnant ice masses contributed only 

minor amounts of sediment to the glacial melt-water 

deposits.

The relatively narrow width of the stagnant zone is 

defined according to maximum length of elongate icecontact forms such as eskers and ice-channel fillings at 

the heads of individual sequences. The proximity of active glacier ice to the stagnant zone during deglaciation 

is suggested by the relatively few, but widely scattered, 

localities at which end moraines or evidence of minor 

glacier readvances are present.

Detailed surficial mapping of 7V2-min quadrangles 

over all major parts of southern and central New 

England has shown the widespread distribution of morphosequences and their relation to ice margins during 

deglaciation, and has demonstrated that the Laurentide 

ice sheet retreated systematically northward by the 

process of stagnation-zone retreat.
16 SYSTEMATIC ICE RETREAT IN NEW ENGLAND

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FIGURE 13.—Shear planes containing debris, Casement Glacier. A, Axe at intersection of 

shear plane with ice surface. Iron-rich debris, derived from a local source, traveled up 

shear plane dipping to left. B, Extension of shear-plane intersection with the ice surface. 

Iron-rich debris contrasts with gray scree carried along the ice surface.
SUMMARY 17

* c

I,

4

^

D

I

•* +•

FIGURE 13.—Continued. C and D, Shear planes containing locally derived iron-rich debris 

in an area of the Casement Glacier where scree is absent. Shear zone appears to pinch out 

in foreground of C. Moraine in distance has a core of ice. Shear planes in C and D dip to 

the right. Photographs taken July 1975.
18 SYSTEMATIC ICE RETREAT IN NEW ENGLAND

FIGURE 14.—Debris on Casement Glacier derived from shear planes FIGURE 14.—Continued. B, Shear plane in ice dipping to the left. Note 

near the area shown in figure 13. A, Axe on intersection of glacier that the large clasts along the shear plane are much rounder than the 

surface and shear plane that dips sharply up ice to the right. Debris clasts in the scree shown in figure 10. Photographs taken July 1975. 

is concentrated left of the axe, and the surface debris zone can be 

traced toward the viewer.

FIGURE 15.—Casement Glacier. A, Looking southeast. Photograph by Austin Post, August 1964. B, Looking northeast. Photograph taken 1975. 

Morainal debris near center of the glacier is a thin surface accumulation. Debris covering the area at the edge of the glacier is interpreted as 

having been derived chiefly from the dirt machine, as explained in the text.
REFERENCES CITED 19

FIGURE 15.—Continued.

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20 SYSTEMATIC ICE RETREAT IN NEW ENGLAND

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