C-Change Working Paper:

Coastal and deposition in the Cap laRonde-Goulet sector of Isle Madame, Breton , Nova Scotia

by

Eric R. Force Geoscience Department University of Arizona, Tucson AZ 85719 US ([email protected])

C-Change Working Paper May 2012

Published by the C-Change Secretariat (Canada) Telfer School of Management, University of Ottawa C-Change ICURA Working Paper Series No. 40

This document is prepared as a public discussion document among C-Change communities as part of the C-Change ICURA Project 2009-2015 (www.coastalchange.ca) and with the permission of the C-Change Secretariat (Canada). This paper has not been subjected to peer review or other review processes and does not necessarily represent the position of individual C-Change Community Partners or researchers. This work is presented to encourage debate and enhance awareness of environmental change among coastal communities in Canada and the Caribbean. © C-Change

Correspondence on this paper should be directed to the C-Change Secretariat, c/o C-Change Administrator, Telfer School of Management, University of Ottawa, 55 Laurier Avenue East, Ottawa, Ontario CANADA K1N 6N5 email: [email protected] Telephone: +1 (613) 562-5800 x2933

C-Change Secretariat (Canada) www.coastalchange.ca C-Change Secretariat (Caribbean) Telfer School of Management, c/o Sir Arthur Lewis Institute of University of Ottawa Social & Economic Studies (SALISES) 55 Laurier Avenue East University of the West Indies, St. Augustine, Ottawa ON K1N 6N5 Canada Trinidad and Tobago, West Indies Tel: (613) 562-5800 Post 2933 Telephone: (868) 662-6965 Email: [email protected] E-mail : [email protected]

C-Change Working Paper #40 Force

Abstract

The study area, a 6-km stretch of along the southern entrance to St. Peters , invites study because of its strategic position and its documentation through about 238 years of its history. Cap laRonde and adjacent capes are eroding drumlins, and Goulet Beach/Island has been at various times a gravelly or a large . Erosion of Cap laRonde and other capes, by wave undercutting (“Roman-nose profile”) and by slump of -cliffs (“boxer’s-nose profile”), has occurred throughout this history, but at Cap laRonde erosion accelerated about 1970 from 0.8 m /yr or less, to 1.3 m/ yr or more. Concurrently, the that extends to Cap laRonde has narrowed from 120 m to 60 m by beach retreat. Acceleration of erosion is due to some combination of sea-level rise, mining of gravel and from several , and retreat of the Cap laRonde from a bedrock platform, all of which are consistent with the observed timing of acceleration. The study area is especially sensitive to sea-level rise because the surface separating bedrock from glacial deposits is near present sea level and its slope is very low. Mining has been of sufficient magnitude to systematically deprive two important coastal compartments of a supply of gravel and sand since about 1970, suggesting great importance of this factor in governing local erosion rate. The evolution of Goulet Beach is out of step with the erosional chronology, and has changed little since the 1970’s, but extended, translated, and reshaped itself markedly in previous periods. It is likely that evolution of this beach was internally controlled in part by erosion and reworking of a nearby glacial feature that has been eroded. Extrapolation of erosion rates with adjustment for changing geometries and processes suggest that Cap laRonde will vanish as a glacial geomorphic feature by 2040, and subaerial parts of the tombolo soon thereafter. Accelerated alterations in adjacent areas may follow.

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Coastal erosion and deposition in the Cap laRonde-Goulet Beach sector of Isle Madame, Cape Breton Island, Nova Scotia

1. Introduction

Context of the area and this study

Rapid modification of drumlin-dominated shorelines is common on the of Atlantic Canada and New England, and poses problems not only to coastal navigation, wetland protection, etc., but to increasingly valuable land holdings there. This paper presents a time- series study of such modifications along a 6-km stretch of coast on Isle Madame, Nova Scotia (fig. 1) based on personal observation, air photos, and maps as old as 1770; the changes are related where possible to observed modern processes. The “drumlin coasts” of Nova Scotia were the subjects of early attention by Goldthwait (1924) and Johnson (1925), and Nova Scotia has remained a center for such studies (Wang and Piper, 1982; Boyd et al., 1987; Carter et al., 1990; Manson, 2002). However, between Framboise, 46 km to the NE of the study area (Wang and Piper, 1982) and Chezzetcook and Musquodoboit , over 200 km to the SW (Boyd et al., 1987; Carter et al., 1990), there are no detailed descriptions of coastal change. The stretch chosen for study centers on Cap laRonde and Goulet Beach/Island at the northeast corner of Isle Madame (fig. 1), at a point of transition from conditions facing SE toward the open sea, and those to the NW sheltered by the Lennox Passage between Isle Madame and Cape Breton Island. To the NE stretches St. Peters Bay, which in turn gives access to the Bras D’Or “Lake” system, via a narrow (now a canal) that was already strategically important for Indian trade and French colonial and military interests in 1650 (and much later for ships seeking to avoid German submarines). Throughout this area, Cap laRonde is a navigational landmark. It is its position re navigation into this approach that resulted in the study area being described and mapped so early (fig. 2). The area is also blessed with unusually early air photo coverage and high-quality landscape photos, and is thus well suited for time- series analysis. Cap laRonde and adjacent capes seemed likely to function as a linked system with intervening beaches, including those extending as far as Goulet Beach/Island (fig. 3). However, seemingly simple questions of sediment budgets, etc. prove to be complicated by several factors, among which are sediment inherited from now-vanished glacial features, changes in rates of retreat, and mining of gravel and sand from the beaches. Accordingly this study has focused on those factors.

Physical setting

The topography of the study area is low-lying and dominated by drumlins, many of which have become partially submerged, intersecting sea level to form an anastomosing (fig. 3). The area is entirely under 30 m elevation, and sparsely populated, with most land forested. Bedrock consists of north-dipping clastic rocks of Carboniferous age (Force and Barr, 2006; Giles et al., 2010). Rock exposure is entirely along the shore; no inland exposures have been found despite extensive development of valleys at 5 m elevation or less. Thus the general slope on the bedrock surface must be exceedingly low, probably averaging 1 in 150 or less. This

MAY 2012 Page | 3 C-Change Working Paper #40 Force surface of course shows reversals in the direction of surface slope where exposed in whaleback outcrops along the shore. The bedrock surface where exposed shows striations indicating glacial movement in several directions, with those to the ESE predominating (Stea et al., 1992; Grant, 1994). Drumlin elongation in the study area is consistent with these directions (fig. 3) and glacial till there predominantly represents the older stages of Wisconsinian glaciation. Drumlins in the study area are typically as much as 300 m long, 100 m wide, and 25 m high. Glacial till is exposed where these drumlins are eroding as cliffed , and is a semi- indurated reddish aggregate of boulders to , grit to sand, and reddish silt to clay in roughly equal proportions. Most clasts are derived from sedimentary rocks, some local. Cap laRonde is the most prominent coastal headland, flanked by two others called Gull Cape and another I will informally call “Mine Bluff” (labeled 620 on fig. 3; it was not a cape until adjacent beach mining made it so). Farther to the south at Cap Petit Nez (fig. 1) are several more sea cliffs formed from drumlins. Drumlin headlands of the study area, especially Cap laRonde and “Mine Bluff”, are perhaps unusual among those described in the literature in their steep slopes; overall angles of 70 degrees or more are characteristic, and overhanging turf at the top and large wave-cut notches at the base are common. Such headlands are those eroding fastest; headlands with lesser angles, such as about 45 degrees for Gull Cape, are vegetated and fairly stable, although subject to slumping and rill erosion. Of these cliffed headlands, only Cap laRonde shows indications of being a drumlin that was formerly cored by rock. Its bedrock is now exposed only offshore at low tide in the direction of former drumlin elongation, as part of a large of residual boulders. The present cliff face, however, consists entirely of eroding till. Cap laRonde is topographically isolated from neighboring headlands, and is tied to the shore by a tombolo about 600 m long (fig. 3). This tombolo consists of gritty to cobbly shingle; the shore facing south is the more active as shown by its washover fans. Some of this material has been mined as described below. Similar steep shingle beaches link all the eroding-drumlin headlands of the study area. Locally and seasonally they may be sandy or gritty as surface veneers, but they are underlain by coarse-grained material and backed by similarly coarse beach crests and washover fans. The beaches are occasionally breached to form inlets, generally short-lived. The beaches typically enclose ponds or (“barrachois”), which may include small tidal deltas and active or drowned salt marshes. Goulet Beach (or Island, also known as Long Beach or Island; henceforth the Goulet) is the only large spit in the study area (fig. 3). Like the other beaches, it is composed largely of gravel, though sand accumulates seasonally along both and along the interiors of its recurved portion. Since 2006, a spit and washover fan of eastern Goulet has extended to Potato Island, so that Goulet is no longer an independent island. Mining of gravel and sand from the SW end of the Cap laRonde tombolo has continued to the time of writing (2010). Mining in this area began about 1970, and proceeded under a succession of landowners. Though material could legally be removed only above and behind the high-tide mark, there are photos of some mining on the beach face. Gravel and sand were also mined in the 1940’s toward the NW end of Goulet Beach/Island. The marine environment of the study area is also quite pertinent to this paper. Very little sediment is contributed to this environment by fluvial processes. The area is mesotidal, with 1-2 m tides, but tidal currents and tidal seem of minor importance in the distribution of coarse sediment. Wave-driven processes are much greater, but vary greatly within the area with both time and place because of variable wind direction and variably protected shores. In adjacent

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open , winter waves are generally 1.5-2.5 m, but most years provide some waves of greater than 8.5 m height (Wang and Piper, 1982; Shaw et al., 1993). Tropical storms and coast- following circulatory storms can be accompanied by storm surges as much as 1.5 m (Shaw et al., 1993). The rate of sea-level rise is about 5.6 mm/yr at present along this shore, consisting of a eustatic component currently about 3.1 mm/yr (IPCC, 2007), and a glacial forebulge-collapse component (after Quinlan and Beaumont, 1981) of 2.5 mm/yr (subtracting the pre-1993 eustatic component of 1.8 mm/yr from measured tide-gauge measurements prior to 1993 of 4.3 mm/yr at nearby Point Tupper, from Shaw et al., 1993).

2. Methods

The author lived in the study area, allowing frequent inspection and thus a study of the distributions of responses to recent seasonal and meteorological events. For example, distribution of erosion for individual events was established in part by freshly slumped (commonly overturned) green turf at the bases of seacliffs, prior to removal by the next event. Conversely, aggradation could be established after an event by deposition of fresh sediment on still-green vegetation. My measurements of erosion rates are from clifftops to pre-existing permanent structures, most notably the foundations of successive navigational aids at Cap laRonde, measured from 2002 to 2007. The distribution of erosion along these cliffs was monitored with rows of distinctive pebbles a measured distance back of the clifftop as well as the width of displaced turf. Shoreline positions prior to 2002 were established using air photos from 1936, 1953, 1969, 1975, 1983, and 1998. The superposed positions I show have not been rectified; the air photos were scale-corrected xerographically to within 1 percent, registered using the nearest stable in the drumlin archipelago, and superposed using only the central portions of the photos. Successive cliff positions shown are based on cliff tops. Published dates of certain transitions, such as successive lighthouses falling into the sea, the opening and closing of inlets, and the history of beach mining, have been supplemented by my own post-1975 records and the air photos. Prior to 1936, my information on shoreline position is from maps by Bayfield circa 1850, and by J.F.B. DesBarres and Samuel Holland about 1770. These obviously lack the precision of air photos, but I find that they can be registered with the more recent photo information—a testament to the dedication of the mappers. Land-survey plat-maps from 1847 and 1877 are also useful in certain ways—widths of land-holding strips were apparently measured but other dimensions may not have been. I am fortunate to have profiles of landscape features of the area from about 1770 drawn by J.F.B. DesBarres (fig. 2) and from about 1932 photographed by Wallace MacAskill. Various other observations and datable ground-based photos were provided by local residents, notably Patrick Dawson.

Modern processes on cliffs and beaches

The preservation of glacial striations several meters seaward of their eroded till mantle, and their preservation as whalebacks much farther seaward, shows that the rate of erosion of bedrock is negligible compared to that of till (I am aware that softer bedrock assemblages are retreating by seacliff erosion much more rapidly elsewhere in Cape Breton Island; Johnson 1925).

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Erosion of sea-cliffs consisting of glacial till is rather rapid on the two that are steeper than 70 degrees, Cap laRonde and “Mine Bluff”. Gull Cape, with vegetated slopes of about 45 degrees, retreats much more slowly, failing by slump and rill erosion. I have observed this pattern elsewhere near the study area, and it is commonly reported in the literature (e.g. Wang and Piper, 1982; Manson, 2002; Himmelstoss, 2006; Greenwood and Orford, 2007). The profiles of the steep sea cliffs show two end-member morphologies, which I characterize as Roman-nose vs. boxer’s nose profiles (fig. 4). The Roman-nose profile is produced by undercutting of relatively undisturbed till by wave erosion at the base of the cliff, to form a notch cut deepest at high-tide level. The upper cliff has a convex profile controlled by the fall of individual clasts. The turf or root layer at the top projects out as a sort of “brow,” forming an overhang. The boxer’s nose profile, concave toward the top and irregular below, is produced by slumping and subsequent rill erosion that outpace wave erosion. Gentler slopes within these profiles generally mark the tops of slumps. Many profiles juxtapose the two end members in various ways, and one may pass laterally into the other. These two end-member profiles are similar to those described near Boston by Himmelstoss et al. (2006) for gentler slopes. Seasonal and yearly variations in process can produce one profile from another; Roman- nose profiles are common immediately after a storm, and severe winters can promote slumps when the clifftops thaw. Slumps are initiated at the tops of cliffs as tears in the ground surface, commonly about a meter back from the cliff face. The surface along which slumping occurs may remain open to a toe partway down the cliff, but more commonly the toe is near sealevel. The base of eroding seacliffs may be protected by talus ramparts that form a boulder framework extending across the normal tide range. The tops of such ramparts are at grade laterally with the crests of adjacent shingle beaches. I note that the protection afforded by some such ramparts is transitory, especially where they are a veneer on till exposed on the same surface, analogous to a pediment. The coarsest angular clasts of such ramparts are eroded from till of the cliff face, and move only to positions of stability. Such residua form boulder retreat as the cliff erodes back (cf. Wang and Piper, 1982; Carter et al., 1990). Where mudflows have reached the cliff base, sieve deposits analogous to those at the heads of alluvial fans (Bull, 1972) form, the fine fractions having disappeared into the rampart to form its matrix, the coarse fraction left behind as sinuous piles on the rampart marking a locus of flow arrival, eventually to become incorporated in the rampart itself. The part of the coarse-grained debris eroded from till cliffs that can be removed by waves is transported mostly along shore (cf. Boyd et al., 1987) due to oblique wave runup. Coarse clasts in the nearshore are commonly thrown back into the tidal zone by storms, as shown by remnant kelp holdfasts and bryozoan coatings. Longshore transport produces gradients in the size of coarse clasts (cf. Boyd et al., 1987), most notably on the southern arm of the Cap laRonde tombolo when in storm-beach mode. Coarse material transported along shore is largely confined by headlands to form coastal compartments (cf. Boyd et al., 1987), but bypass must also occur in extreme events. Shore protection in winter by ice floes and shorefast ice can be an important process on northern Canadian coasts (Forbes and Taylor, 1994) but was not observed in the study area. Protection by kelp mats occurs from time to time. Plumes of fine-grained red sediment can be seen extending offshore (also visible in air photos, as noted by Grant 1994, fig. 69). This sediment can contribute to the Holocene deposits of adjacent bays (Robert Taylor, pers. commun., 2005; cf. Boyd et al., 1987). The plumes may linger after the storm that initiated them, until all the rounded boulders of till rolling in the surf have worn down. My observations of processes forming the beaches of the study area are sketchy. The

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beaches vary in profile from season to season, due to temporary aggradational ridges, temporary protective kelp mats, short-lived storm breaches and associated washover fans, etc. Because most of the beaches are tied to headlands that are eroding, those beaches are retreating. Indeed, lagoonal peat overlies wood in growth position (balsam fir; C. Laroque, pers. commun., 2005), exposed in the face of the beach that ties Cap laRonde to Gull Cape. Similar wood underlies Spartina peat in the marsh in back of this beach. Apparently a forest drowned by rising sealevel became colonized by marsh forms, and was then exposed when the beach retreated. Gravel and sand mining forms pits behind the crest of the western end of the southern arm of the tombolo at Cap laRonde (fig. 3). After stormy periods, washover fans and Gilbert- style deltas of freshly deposited coarse material are found in these pits, no doubt to the delight of the miners, but showing that beach retreat in this sector occurs partly by mining-related depletion of available material on the beach face. Washover fans are supplied via short-lived inlets that open into a pit, at the expense of the beach. The same process has undoubtedly occurred at currently-inactive beach mining operations elsewhere in the study area (fig. 3) and the region. The evolution of Goulet Beach/Island is apparent from accretionary ridges in its recurved spit portion that are visible in air photos; these show retreat of the beach front but extension to the NW. This is consistent with current depositional patterns I have observed; little accretionary ridges wrapping around the entire end of the spit have resulted from several events during the period of observation. Longer-term evolution of this feature will be discussed below.

Rates of shoreline change

Erosion of till in seacliffs is common throughout the region of the study area, mostly occurring during storms. The most severe events that took place in my 2002-2007 monitoring period include tropical storm Gustav of early September 2002, the severe winter (and following thaw) of 2002-2003, and an unnamed storm of February 1, 2006 accompanied by strong NE winds and storm surge. The last was most severe in Rocky Bay but formed new washover fans behind shingle beaches throughout the area, opening a temporary into Mauger Pond but closing one between Goulet and Potato Islands. Figures 1 and 3 show the distribution of erosion associated with the Gustav storm, which produced a storm surge and strong SE, then NE winds in St. Peters Bay, and washed over or breached several shingle beaches in the area. Its erosional pattern was complex—minor on some exposed till headlands, severe on some protected ones in Lennox Passage, but worst on “Mine Bluff”. The rate of erosion of Cap laRonde is nearly constant over the seven years of measurement (and more so than the weather). The average loss is 1.38 m per year; in detail the loss is stepwise (as shown in figure 5 in dashes) due to inhomogeneous retreat of the clifftop and to storm events, but departures from linearity are relatively minor (added note—the winter of 2007-2008 produced a retreat of almost 2 m). Rates of retreat this great are not uncommon in analogous drumlin headlands of Nova Scotia (Wang and Piper, 1982; Boyd et al., 1987; Carter et al., 1990; Shaw et al., 1993; Manson, 2002) but are startling to residents and neophytes alike. “Mine Bluff” has been retreating somewhat more slowly, averaging about 0.6 m per year over the period of the study, but I have measured the position of its clifftop too sporadically to present a graph.

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3. Chronology of Shoreline Change

The availability of air photos for 1936, 1953, 1969, 1975, 1983, and 1998, the ground- based photos from the 1930’s through 1970’s, land-survey plat-maps from 1847 and 1877, the maps of Bayfield of about 1850 and of DesBarres and Holland of about 1770, together with the current morphology of the study area as described above, permitted compilation of longer-term shoreline change. Cap laRonde and adjacent beaches.—Figure 6 shows the changes in cliffs and beaches at Cap laRonde from air photos. Note that as recently as 1975 the tombolo was double; a pond between the shingle beaches leading to the cape was present. In previous air photos it was larger and some relict glacial landforms projected through it. The remainder of this pond is now covered by washover fans derived from the beach to the south. Figure 7 shows the change superposed on a photo by Wallace MacAskill, taken about 1932 from the beach to the SW (a position now out to sea). The foundation stones of the lighthouse slowly fell into the sea from 1970 until 1973; one of the barns to its west became a substitute lighthouse for a few years. In this period the headland was not only shortened but also narrowed, as shown by the truncation of the road on its southern flank. Subsequent to lighthouse abandonment, a series of unmanned navigational aids were installed; the foundations of two of them fell into the sea also (the winter of 2001-2 and the spring and summer of 2003) and can be seen amongst the rocks at the base of the cliff. Together with the abandoned foundation of the third one, they mark a path of cliff retreat oriented about S80E (the former trend of the top of the drumlin). Currently no navigational aid is present at Cap laRonde. Out of sight behind the cape in figure 7, timber cribwork was installed sometime in the early 1900’s to protect the base of the cliff from erosion along that flank. Remnants can still be seen, but by the 1940’s, it had ceased to be effective. The data from photos suggest approximate average rates of retreat of Cap laRonde of 0.76 m/year from 1936 to 1975, and 2.31 m/year from 1975 to 1998. The seacliff became steeper also between the 1960’s and the 1970’s (Fig. 7). The 1874 plat-map, which shows the lighthouse, can be used to calculate an erosion rate for the 1874-1970 interval (previous to the foundation beginning to fall over the cliff). That rate is 0.34 m/year. The DesBarres map shows sufficient detail to approximate the position of the cliff at the end of the drumlin in 1770. This suggests that as much as 80% of the drumlin remained; if so, an average for cliff retreat for the entire 237-year period would be a maximum of 0.7 m/year. Thus the time around 1970 appears to mark a significant change in the rate of geomorphic change at Cap laRonde, from relatively slow cliff retreat before that time, to a rate that is about double or more afterward. The shingle beaches that tie Cap laRonde to adjacent capes also underwent dramatic changes in the post-1847 period (Fig. 6). They evolved from two separate beaches enclosing a pond and relict glacial features, remarkably similar from 1847 to 1936 and recognizable as late as 1975, to a single narrow feature consisting basically of the washover fan of the south-facing beach. The narrowest width of the isthmus decreased from about 120 m in 1847, 1877, and 1936, to about 100 m in 1975 and 60 m at present. The difference is largely due to retreat of the south-facing beach. The beach face there consists largely of pea-gravel as described above; apparently the beach face is an “outcrop” of mine tailings and older washover fan material deposited when the beach was in its prior position to the south. “Mine Bluff”, which did not project into the ocean until after 1936, became a cape subsequently by retreat of adjacent beaches. The beach at its southeastern corner moved back about 50 m between 1969 and 1975.

Goulet Beach/Island.--The same sources of information were used to compile a history of

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the Goulet. Map information that predates the airphotos is of course difficult to register accurately, but the DesBarres map in particular appears to be of remarkably high quality. Figure 8 shows my approximation of shore positions. Clearly the Goulet has been a recurved spit at its NW end since at least the late 1800’s and this end has extended since that time. Note also that the NW end has translated or pivoted shoreward; this is supported by the truncation of the accretionary beach ridges within the recurved area (Fig. 9) by the present shore. The Goulet became an island, i.e. decoupled from Gull Cape, in 1996, by the formation of a pair of shallow inlets (fig. 3). However, the Goulet became linked with Potato Island in 2006 via greater recurvature of its eastern margin. The earliest map, by DesBarres, shows the area of the Goulet as a chain of three islands. The northernmost island on the DesBarres map is a feature that can be interpreted in different ways; this is the feature DesBarres labelled Fish Isle (Fig. 8). It could be simply a temporarily detached segment in a chain of barrier islands, and if so the evolution of the island chain has been uniformly that of extending and pivoting except for opening and closing of inlets. I think the state of Fish Isle in 1770 was more complex; it is not shaped or patterned like the barrier islands on DesBarres’ map and is out of line with the island chain (Fig. 8). Probably it reflected some stage of re-equilibration after or during erosion of a drumlin there. Post-1770 evolution then records progressive erasure of the traces of the drumlin by closure of the inlet to its SE, and smoothing of the beach by longshore transport. Erosion of this drumlin is consistent also with the subsequent shoreward pivoting of the beach. The gravelly accretionary beach ridges preserved within the Goulet (Fig. 9) are a clue to its evolution. The preserved ridges are now below high tide, but each one rises to the north (where each is truncated by the modern shingle beach) and plunges under younger intertidal to the south. In this transition, sediment of each ridge loses from 10-15 cm on the north end to 5-9 cm on the south. This suggests derivation from a source to the north within the Goulet system, probably as a series of bars, partly subaerial. Their shape and location are like that of the western arm of Fish Isle as shown by DesBarres (Fig. 8), and their low elevation may reflect the lower sea-level of that time (since DesBarres first studied the area, sea level must have risen almost a meter.) The in situ frost-shattering of gravelly clasts in the ridges suggest considerable age. Progradational features progressively submerged by rising sea-level are commonly observed on Cape Breton Island (Grant, 1994). A shoal oriented ENE is present on the eastern margin of the former Fish Isle (Fig. 8). It projects into St. Peters Bay for 500 m and consists of anomalously coarse angular material. The 1936 and 1953 air photos show a possibly of bedrock at its NE end. Several origins seem possible. It could be a retreat shoal in part, formed from the boulders shed off the eroding Fish Isle drumlin and accumulated along its side, as is common elsewhere in the region (Taylor and Shaw 2002). Or it could be a central remnant of another drumlin possibly cored by rock, the shoal representing the fraction of till too coarse to be transported by waves. Figure 8 shows that the change in the Goulet between 1975 and 1998 is the least of any period in its history for which I have records. In this respect it is out of step with the erosion of Cap laRonde and adjacent capes. The faster change in the Goulet in earlier periods may reflect equilibration in the aftermath of erosion of the now-vanished drumlin north of Fish Isle. In any case, the tempting conclusion that the Goulet grows as a result of erosion of Cap laRonde can only be part of the explanation.

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4. Factors Accelerating Shoreline Erosion

Rapidly eroding drumlin coasts are common in Atlantic Canada. The acceleration of erosion suggested in the study area may or may not have implications elsewhere, depending on which mechanisms are unique and which are widespread. Three main interconnected factors seem to be involved in the rapid and accelerating erosion of Cap laRonde and adjacent capes. The first is rising sea level, which applies to all of Nova Scotia. Its effect in triggering has been documented there by several authors, e.g. Shaw et al, (1993). Komar and Shih (1993) have been able to isolate the effect of rising sea level on coastal erosion along the Oregon coast; the segments that are eroding rapidly are those in which relative sea level is rising. A more pertinent analogy can be constructed by comparing the Nova Scotia studies including the present one, with an otherwise analogous one by Greenwood and Orford (2007) in Ireland where sea level is relatively stable--and sea-cliff erosion rates significantly less. Along glaciated coasts, the immediate effect of rising sea level is sensitive to the elevation of bedrock surfaces surmounted by till, and in the longer term to the slope of that bedrock surface. Bluffs that are not retreating sit on bedrock surfaces just high enough to provide protection from wave erosion, or are protected by headlands that are. If this state can be considered one of stable equilibrium, configurations deprived of this degree of bedrock protection are unstable, and as sea level rises all the bluffs fit this description. The degree of instability and much of the kinetics of erosion depend on the slope of the bedrock surface. In this context, even the small annual increments of sea-level rise are of importance. For example, in the study area where the general slope of the bedrock surface is less than 1 in 150, the annual sea-level rise of 0.56 mm implies at least 0.8 m of shore thrown into instability. Shorelines in the study area that are retreating more slowly than this are lagging due mostly to slower kinetic development and other factors. As we have seen, the kinetics of erosion are indeed locally impressive in the study area, but broadly understandable, even inevitable, seen from this perspective, and an increase in the rate of sea-level rise should generally correspond to an accelerated rate of erosion. The second factor is closely related and deals with local variations in bedrock slope. Where drumlins rest on glaciated whaleback outcrops or other local bedrock highs, the rate of wave erosion will vary with position of the shoreline relative to the bedrock surface. Cap laRonde was apparently a rock-cored drumlin, resting on bedrock now exposed offshore at low tide. During most of the erosional history of this drumlin, part of its till sat atop rock at or above the lower sea-levels of those times. Much wave energy was dissipated on this rock, which eroded very slowly. Once erosion had eaten away the till sitting on emerged rock, which probably occurred in the 1960’s (Fig.7), the rate of erosion must have accelerated because wave energy was focused on till and boulders resting on till. The efficacy of this effect is demonstrated by an outcrop of till at the west end of the study reach (labeled 20 in Figure 3), which was similarly perched on rock until the last few decades. This bluff is now retreating rapidly (about a meter per year average) after a century of relative stability, despite being in a relatively protected site in the Lennox Passage. The third factor, also local, is the mining of back-beach gravel and sand. Since mining 3 began about 1970, the volume of mined gravel and sand is on the order of 100,000 m . The magnitude of beach retreat on the south arm of the Cap laRonde tombolo virtually mimics the width of mined gravel, i.e. the modern beach position follows the back end of the mine in the 1983 air photos. The retreat of this beach due to mining has of course increased the exposure of

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adjacent headlands to wave erosion; the tendency of beaches to be tangential to headlands can be maintained only by headland erosion if beaches retreat. Note that all three factors are consistent with the observed increase in erosion rate around 1970, indeed two of the factors actually pivot there. This makes it impossible to attribute a single cause to accelerated headland erosion. Since all the factors are known to have some local importance, and all show the same timing and direction, one should not be trying to find a single cause; the three factors are all components of the change. However, an analysis of material flux in beaches adjacent to Cap laRonde provides evidence that mining is the most important factor there.

5. Fluxes

The current rate of retreat of Cap laRonde, translated into volume loss, is about 2000 3 m /year (1.38 m retreat x 15 m average bluff height x 100 m bluff length). The average till 3 composition implies that this comprises about 650 m each of gravel, grit/sand, and fines. The fines are lost to offshore deposits, but coarser material transported alongshore is divided into material transported westward north and south of the cape. The relative sizes of 3 washover fans suggest that about 1000 m /year is transported along the south-facing beach, and 3 the remainder, about 300 m /year, to the north. These rates of supply were probably greater as far back as about 1970, because a greater cliff perimeter was eroding at similar rates. Before that time, greater perimeter eroding at lesser rates supplied material at unknown rates, possibly similar to that of the present. Since 1770, when 80% of the drumlin was still present, 3 approximately 300,000 m have been removed (200 m of drumlin length eroded with average 3 height of 15 m), consisting as at present of about 200,000 m of gravel and sand. Erosion of the other two capes of the study area also supply material, probably at roughly similar rates to Cap laRonde because their slower retreat rates are balanced by their greater perimeters. The 1770 profiles of these capes (fig. 2) suggest that their erosion histories are similar to that of Cap laRonde, though the eroding perimeter of “Mine Bluff” was relatively small before 1936. Material eroded from all the capes contributes to adjacent beaches, and to more distant beaches at times when by-passing is possible. Roundness and grainsize gradients suggest that transport is generally away from Cap laRonde along both arms of the tombolo. The northern fraction of Cap laRonde material plus that from Gull Cape may have yearly contributed a thousand or more cubic meters of gravel and sand to the Goulet when continuous longshore transport was possible, i.e. probably most of the time from 1850 to 1996. Retreat of the beach between Cap laRonde and Gull Cape, and the 1996 opening of shallow inlets between Gull Cape and the Goulet, must have decreased this flux; the impressive roundness of material flooring these inlets suggests little bypassing there at present. Beach mining of gravel and sand is a significant term in flux equations of the area. For 3 example, the approximately 80,000 m apparently mined from the south arm of the Cap laRonde 3 tombolo is roughly double the amount of new material (1000m of sand and gravel/year for 40 years) supplied by erosion of the cape and transported along this arm during the period of mining. The resulting retreat of the beach and emergence of “Mine Bluff” as a prominent headland has turned this beach into an isolated compartment that makes sediment by-pass 3 difficult. The northern arm of the tombolo, where both mining (about 15,000 m ) and sediment

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3 supply (about 300 m /year) are less vigorous, has retreated also and bypass around Gull Cape made difficult. Despite rising sea-level, beach aggradation is common in Nova Scotia where sediment supply is sufficient (e.g. Shaw et al., 1993). The tombolo would seem a candidate for such aggradation were it not for mining, because of the increased rate of supply in a system formerly at equilibrium. However, aggradation has not occurred, providing an indication of the result of mining. Beach mining must be the most important cause of acceleration of shoreline retreat at the beach, and in an integrated shore system this conclusion has implications for the rate of headland retreat; accelerated headland erosion is due in considerable part to mining of adjacent beaches. The period of greatest elongation of the Goulet predates 1975, a period when both internal adjustments to the destruction of glacial landforms and longshore supply from headland erosion could contribute. After 1996, when inlets opened and the between Potato Island and the Goulet become a sink for sand deposition, supply by headland erosion would have become more limited. We have seen that the evolution of the Goulet is out of step with that of erosion of the capes--from the 1970’s on, the Goulet changed more slowly (fig. 8). The simplest explanation is that mining of beach gravels, known to have occurred on this northern margin of the tombolo also, quantitatively intercepted the supply of the gravel fraction.

6. Predictions

Given the material fluxes and rates of change described above, it should be possible to project forward in time, i.e. to predict the evolution of some features of the study area. This cannot be done with any confidence for more than a few decades, as factor interactions and new variables may complicate the analysis. For factors with anthropogenic components, alternative outcomes must be considered. The simplest prediction seems to be that for Cap laRonde. Even if the beach-mining operation were to cease immediately, the disappearance of the Cap as a relict glacial feature seems assured (as noted by Cameron, 1998, p. 52-3). Current rates of erosion, if extrapolated linearly, would predict complete erosion by 2074. Since the Cap is being eroded on three sides in a positive-feedback context, perhaps a more realistic estimate is 2040. It seems unlikely that any shutdown of mining activity would translate into erosional stability that quickly. Indeed, the other factors in accelerated erosion would be unaffected. Coastal drumlins commonly vanish along Nova Scotia’s shores, eroding to become boulder retreat shoals. Two rather prominent examples in Nova Scotia are Misener’s Island east of Halifax (Carter et al., 1990) and Petitpas Island near Canso. The process may take up to 2000 years (Carter et al., 1990). The resulting shoal consists of the material too coarse to transport away, anchored to an outcrop if the drumlin was rock-cored. The shoal may be arranged as two “spurs” that represent the former sides of the drumlin (Taylor and Shaw, 2002). This shoal may be a long-lived feature (assuming constant sea level and wave energy). We can guess the initial shape of the shoal derived from Cap laRonde--a narrow linear neck (the current tombolo’s isthmus), subaerial on the west, ending in a shoal (dangerous to navigation) shaped in plan like its precursor drumlin, consisting of loose blocks (including navigational aid foundations, etc.) and rock outcrop exposed only at low tide. Note the similarity to a shoal that already exists in the study area, the ENE-oriented spur of Goulet Island that has existed since 1770. The Cap laRonde shoal, being subject to higher wave energy and faster sea- level rise, will probably not last as long.

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Later on, the neck will only be a projection at low tide from the Isle Madame shore. At this point, the new bluffs south of Cap laRonde and Gull Cape will lose any protection they now enjoy from Cap laRonde and will retreat more rapidly despite their size. Other drumlins to the south (figs. 1, 3) that currently impinge on the shore very little will become the foci of erosion, and form seacliffs. Without knowing how the eroded material will be distributed, and whether Petit Nez cape will have been eroded by this time, I cannot predict how other features will be affected. But this coastal compartment will have the character of seacliffs formed by eroding drumlins through the foreseeable future, as sea-level rises and shore erosion planes them off (cf. Wang and Piper, 1982; Carter et al., 1990). Goulet Beach/Island seems to have reached a quasi-equilibrium following extensive reshaping related to the former Fish Isle, and currently is receiving little coarse material flux from outside its own system. It is possible that little change other than minor northwestward extension, reshaping, and shoreward translation (due to rising sea level) will occur, though the process of segmentation into short segments separated by inlets may continue at the eastern end of the Goulet (in the manner described by Carter et al., 1990). When Cap laRonde is completely eroded, Gull Cape will be less protected, and greater longshore transport to the west of material eroded from it may close the intervening inlets. If so, the Goulet may again lengthen or even prograde.

7. Conclusions

The chronology of shoreline change and the process rates described here point toward a picture of shifting patterns of distribution and dispersal of sediments as seacliffs on individual drumlins are eroded, isolated bedrock highs find themselves at sea, and inlets open and close, all accompanied by sea-level rise. The exact patterns are unique to the study area, but similar to those observed elsewhere in the region. Two elements among these patterns, however, are anthropogenic, and they appear to be of great importance in the accelerated evolution of the patterns since about 1970. These are accelerated sea-level rise due to global climate change, and sediment transport by motorized vehicles, i.e. beach mining, depriving coastal compartments of their natural endowments.

Acknowledgement

The advice and reviews of Robert B. Taylor greatly improved the content and presentation of this paper. Local residents especially Patrick Dawson contributed many observations.

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8. References

Boyd, R., Bowen, A. J., and Hall, R. K., 1987, An evolutionary model for transgressive sedimentation on the eastern shore of Nova Scotia, in Fitzgerald, D. M., and Rosen, P. S., eds., Glaciated Coasts. Academic, San Diego, p. 87-114.

Bull, W. B., 1972, Recognition of alluvial fan deposits in the stratigraphic record, in Recognition of ancient sedimentary environments: Society of Economic Sedimentologists and Mineralogists Special Publication 16.

Cameron, S. D., 1998, The living beach: Macmillan, Toronto.

Carter, R. W. G., Orford, J. D., Forbes, D. L., & Taylor, R. B., 1990, Morphosedimentary development of drumlin-flank barriers with rapidly rising sea level, Story Head, Nova Scotia. Sedimentary Geology v. 69, p. 117-138.

Forbes, D. L., and Taylor, R. B., 1994, Ice in the shore zone and the geomorphology of cold coasts: Progress in , v. 18, p. 59-89.

Force, E. R., and Barr, S. M., 2006. A Lower Carboniferous two-stage extensional basin along the Avalon-Meguma terrane boundary: evidence from southeastern Isle Madame, Nova Scotia. Atlantic Geology v. 42, p. 53-68.

Giles, P.S., Naylor, R. D., Teniere, P. J., White, C. E., Barr, S. M., & DeMont, G. J., and Force, E. R., 2010, Bedrock geology map of the Port Hawkesbury area (NTS 11F/06, 07, 10, 11, and 15; scale 1:50,000). Nova Scotia Department of Natural Resources, Mineral Resources Branch, Open File Map ME 2010-006

Goldthwait, J. W., 1924, Physiography of Nova Scotia. Geological Survey of Canada Memoir 140, 179 p.

Grant, D. R., 1994, Quaternary geology, Cape Breton Island, Nova Scotia. Geological Survey of Canada Bulletin 482, 159 p.

Greenwood, R. O. and Orford, J. D., 2007, Factors controlling the retreat of drumlin coast cliffs in a low energy marine environment—Strangford Lough, Northern Ireland: Journal of Coastal Research v. 23, p. 285-297.

Himmelstoss, E. A., Fitzgerald, D. M., Rosen, P. S., and Allen, J. R., 2006, Bluff erosion along coastal drumlins: Boston Harbor islands, Massachusetts. Journal of Coastal Research v. 22, p. 1230-1240.

IPCC (Intergovernmental Panel on Climate Change), 2007, Climate Change 2007 (report AR4).

Johnson, D. W., 1925, The New England-Acadian Shoreline. Hafner, New York.

Komar, P. D., and Shih, S.-M., 1993, Cliff erosion along the Oregon coast: a tectonic sea-level imprint plus local controls by beach processes. Journal of Coastal Research v. 9, p. 747-

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765.

Manson, G. K., 2002, Subannual erosion and retreat of cohesive till bluffs, McNab’s Island, Nova Scotia: Journal of Coastal Research v. 18, p. 421-432.

Quinlan, G., and Beaumont, C., 1981, A comparison of observed and theoretical post-glacial sea- levels in Atlantic Canada. Canadian Journal of Earth Science v. 18, p. 1146-1163.

Shaw, J., Taylor, R. B., and Forbes, D. L., 1993, Impact of the Holocene transgression on the Atlantic coastline of Nova Scotia: Geographie physique et Quaternaire, v. 47, p. 221-238.

Stea, R. R., Conley, H., and Brown, Y. (compilers), 1992, Surficial geology of the province of Nova Scotia: Nova Scotia Department of Natural Resources, Map 92-3, scale 1:500,000

Taylor, R. B., and Shaw, J., 2002, Coastal character and coastal barrier evolution in the Bras D’Or “Lakes”, Nova Scotia: Proceedings of the Nova Scotia Institute of Science, v. 42, p. 149-181.

Wang, Y., and Piper, D. J. W., 1982, Dynamic geomorphology of the drumlin coast of southeastern Cape Breton Island. Atlantic Geology, v. 18, p. 1-27.

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1. Location of the study reach on Isle Madame, Nova Scotia. Also shown is the approximate volume (in cubic meters) of glacial material mobilized by tropical storm Gustav (Sept 2002) at nearby coastal locations outside the immediate study reach. Scale in km. Inset shows location and some features of regional bedrock geology from Force and Barr (2006).

2. Profile of Cap laRonde and adjacent features, included by J. F. B. DesBarres in his 1770 map of the area as an aid to navigation into St. Peters Bay. “Mine Bluff” is on the left, Gull Cape on the right.

3. Map of geologic features in the Cap laRonde-Goulet Beach/Island area. Qt=Quaternary till; H=Holocene coastal deposits; x=bedrock outcrops. Also shown are mine locations, changes in the status of Goulet Island that post-date the 1975 base, and the volume of glacial material mobilized by Gustav (as in Fig. 1) in the study reach.

4. Diagrams of sea-cliff profiles showing two end-member states of rapidly eroding glacial material.

5. Graph showing progressive erosion of Cap laRonde from 2002 to 2007. The solid-line segments are time intervals of closer observation. Also shown is the incidence of two storms described in text.

6. Progression of clifftop and shoreline positions at Cap laRonde from 1936-1998 based on air photos, showing shoal (reef) including bedrock outcrop left by retreat of the drumlin cliff. The pond shown, separating north and south beaches, was once larger but existed as late as 1975.

7. Photo (from SW) of Cap laRonde published by Wallace MacAskill in 1932, with profiles and locations of its seacliff in subsequent years, derived from old photos. Note progressive steepening of profile. To right of cape is the reef left by retreat of drumlin’s seacliff. Photographer’s position is currently at sea.

8. Progression of shorelines, Goulet Beach/Island 1770-1998, plotted relative to 1975 airphoto base. Positions in 1770 and 1850 approximated from old maps; others post-1900 from air photos. Also shown are “Fish Isle” and the approximate alignment of shoal as shown by DesBarres in 1770.

9. Air photo of the NE end of Goulet Beach/Island in 1936, showing internal structure of complex recurved spit prior to mining.

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