SHAILER S. PHILBRICK Department of Geological Sciences, Cornell University, Ithaca, New York 14850
What Future for Niagara Falls?
ABSTRACT Horseshoes and may be so slow in recession proposed increased diversion of water from as to be a quasi-stationary falls, without the falls for production of hydroelectric The recession of Niagara Falls up the immediate change in the level of Lake Erie. power on both the American and Canadian thalweg of Niagara River will be marked by sides of the river required a series of five major events. Event No. 1: The INTRODUCTION engineering studies of the falls, the Niagara Horseshoe Falls will first lower the level of The concept of retreat of Niagara Falls River, and the water yield of the Upper the Chippawa-Grass Island Pool below the from somewhere near the old landing in the Great Lakes. The latter confirmed one of the bottom of the American Channel and Niagara River at the foot of the Niagara fundamental facts of the Niagara River: its unwater the American Falls. The level of Escarpment near Queenston, Ontario, to flow is nearly uniform because of the great Lake Erie may be lowered a few feet at this about its present location was held by some headwater storage capacity of the upper time. The falls will split into two Horseshoes people 186 yr ago. Capt. Enys (1886, p. lakes. Detailed surveys, hydraulic-model at Navy Island, and the Lockport Gorge, the ccxxxii), a Canadian of the 29th Regiment, studies, plans for the preservation and extension of the Upper Great Gorge in wrote, under the date of July 19, 1787, enhancement of Niagara Falls, and interna- the Lockport Dolomite, will fork into two "Among those who favor this opinion is a tional agreement on the quantities of water gorges; the right hand one in the Tona- Mr. Hamilton, a merchant at Niagara and a that might be diverted for power production wanda Channel carrying 70 percent of the man of very good understanding..." Are we resulted from these studies. These were flow of the river and the left one in the better prepared today to interpret the implemented by construction of regulatory Chippawa Channel carrying 30 percent. The recession of Niagara Falls than was Lyell and diversionary structures and rate of erosion of the Lockport Gorge will who in 1830 wrote from England that the modifications to the crest of the Horseshoe vary with the configuration of the Horse- probable rate of retreat was about 50 yds in Falls. Much additional data bearing on the shoe, faster during notch shape and slower 40 yr and that the falls would eventually purpose of this paper resulted from during arch shape, with shallow and deep reach Lake Erie in —30,000 yr? Feather- extensive geologic and subsurface investiga- plunge pools, respectively, as the Upper stonehaugh (1831, p. 21) made a classic tions for gas, oil, salt, groundwater, and Great Gorge has eroded. Event No. 2: The statement on this subject a year later. "If I highway and river transportation in the Horseshoe in the Tonawanda Channel will have not misconceived the operation of this Niagara peninsula. These data are the split into two waterfalls at the upper end of river (Niagara), it will now be seen that the foundation for Figures 1 and 2. The sources Navy Island and for a short period there will elements of this problem are too compli- of these data are listed in Appendix 1. be three Horseshoe waterfalls until the left cated and vague to offer any hopes of a one in the Chippawa Channel, due to its satisfactory solution." Although the infor- NIAGARA FALLS—PAST faster erosion in the softer rocks of the Salina mation developed in the succeeding 142 yr To project the action of Niagara Falls into Group, intercepts the flow on the right side has weakened that statement, its general the future, we must know how and at what of Navy Island. This event will leave the import has not been erased. We have a better relative rates the falls eroded its present right Horseshoe as a dry falls. Event No. 3: basis for interpreting the mechanics of canyon in the Lockport Dolomite, the Upper The Chippawa Horseshoe will decline in erosion of the falls and their recession, but Great Gorge with its Maid-of-the-Mist Pool. height as the Lockport Dolomite dips we cannot estimate the time required for the We must examine the rate of erosion and the upstream to the south until, at a retreat of the Horseshoe Falls to somewhere mechanics of erosion simultaneously, be- height of ~50 ft, it will no longer have the near the head of the Niagara River much cause the mechanics of erosion affect the capability of recession and will remain as a more accurately than could Lyell. rate of erosion. Then we shall consider the quasi-stationary waterfall. Event No. 4: The This discussion of the future of Niagara general rate of recession from the head of the Salina Group will erode to a broad, gentler Falls is a speculation controlled by several Whirlpool Rapids upstream through the sloped gorge in the bottom of which the factors: (1) our knowledge of the action of Upper Great Gorge to the Horseshoe Falls. steep-sided Lockport Gorge will be eroded the Horseshoe and American Falls in the as far upstream as the quasi-stationary Upper Great Gorge during the past 4,000 or Mechanics and Rates of Erosion waterfalls. The rapid erosion to form 5,000 yr; (2) our knowledge of the geology The most stimulating information on the stepped rapids in the Salina Gorge will lead of the Niagara region, particularly the recent past of Niagara Falls is the it upstream to intercept the water in the underlying bedrock; (3) our knowledge of river-bottom map of the Maid-of-the-Mist Tonawanada Channel and divert it into the the hydraulics of the Niagara River; and (4) Pool (1969, produced by Ontario Hydro for Chippawa Channel. Event No. 5: This will our understanding of man's necessities. the Inland Waters Branch of the Department result in the unwatering of the Tonawanda The investigations of the Niagara River of Energy, Mines and Resources of Canada). Channel and the creation of another dry from Lake Ontario upstream to the falls A profile of the thalweg constructed from falls. Near the head of the river beneath the continued through the nineteenth century this map is shown on the right side of Figure Salina Group, the more resistant Bertie and into the early part of this century. They 2. The river bottom is extremely irregular Dolomite and its underlying Onondaga were capped by the magnificent exploratory with numerous deeps and alternating highs. Limestone will be encountered into which and analytical work of Spencer (1907). Each deep represents the location of an the Bertie-Onondaga Gorge will be cut with Gilbert also published his own study of the ancient plunge pool that formed when the a much slower rate of recession by a new rate of recession of Niagara Falls in 1907. Horseshoe Falls stood slightly upstream Horseshoe, the Final Falls. The Final Falls; Six years later, Kindle and Taylor's (1913) from that deep. The extraordinary fact will be much lower than the preceding Niagara Folio was published. By 1950, the about the bottom of the Niagara River and
Geological Society of America Bulletin, v. 85, p. 91-98, 2 figs., January 1974
91
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MAP RECESSION OF NIAGARA FALLS EXPLANATION — Thalweg • Lockport gorge —» Solrno gorge — Ber lie-Onondaga gorge Buried channel • 6- Depth of woter, feet — Crest of present waterfall Salina GORGE Members of Solino Gtoup (See Fi»2J jSA MAJOR EVENTS Horseshoe Foils lowers Chippawa- Orass Island Prol ond unwuters Americon Foils Criippowo Horseshoe Foils captures E• Snorter S Phi lb nek February 1973 Figure I Figure 1. Mtp of recession of Niagara Falls. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 O 0) Q. o O o> < LL. D ^ a> CP Woter Surface 100% I 60 7, aooJ 30QJ 2QQ1 112. iQQj Sea LeveL Points on International Boundary g a a .a q a J.. 1 10 9 T I Future Thalweg 10" Fee* D=Diversion Plunge pools in Lockport and Bertie-Ononda g o Gorges Stepped rapids in Salina Gorge Figure 2. Geologic section along thalweg, Chippawa Channel, Niagara River; Lake Erie to Horseshoe Falls. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 94 S. S. PHILBRICK the Upper Great Gorge is that it is so and 4) reproduced this sketch in juxtaposi- were caused by violent "rock bursts" of non-uniform. It seems that if the Horseshoe tion to a photograph from 1895. The first small pieces of rock that spalled explosively retreated at a uniform rate with its nearly instrumental survey of the crest by Blackwell off the surface of the lock face of the falls to uniform flow and its continuous bedrock in 1842 under the direction of J. Hall (1843) pierce the sheet of falling water like materials, the bottom of the river should defined an arch showing that the notch had projectiles, carrying with them slender, have a relatively uniform slope and generally been erased by continued erosion of the conical capes of water. 1 have observed no in a downstream direction. But here we find flanks. But by 1857 another notch had such jets or comets on my several visits to the a very irregular river bottom in which the developed, and was painted then by F. E. falls during the past 47 yr but this was a plunge pools deepen as we go upstream, Church in his magnificently detailed period of arch configuration, which may be which shows that the falls has receded Niagara Falls, now in the Corcoran Gallery causal or only coincidental. I think it is intermittently at a progressively slower rate. in Washington, D.C. Thus notches can be causal because Barlow's explanation (1877) The high points in the Niagara River bed, considered as normal phases in the head- would be applicable regardless of between these deep plunge pools, are ward erosion of the Lockport Dolomite of configuration, depending on energy to send explainable under historic conditions if the the Upper Grer.t Gorge. the comets or jets skyward upon the relative rate of erosion varied with the The rapid rate of retreat of the falls, when compression of air beneath the falling water. configuration of the crest of the Horseshoe. the crest was notched, was recognized by Laflamme (1906) discounted this explana- My previous argument (1970, p. Gilbert (1907, p. 16) and some who tion and pointed to the open ends of the 3727—3729) is illustrated as follows. Com- followed him. He attributed it to greater curtain of trie cataract as being vents for the parison of the surveys of the arch-shaped frequency of jointing, which means smaller allegedly trapped air. B. Hall (1829, p. crest of 1875 with that of 1886 shows that joint-bounded blocks and hence easier 202—204) found an increase of only 0.04 to during those 11 yr a notch in the right corner erosion of the crest. We don't have to 0.06 inches in barometric pressure behind of the arch retreated almost 200 ft postulate such variation if we consider the the curtain with several hundredths of an upstream.1 A photograph from about 1886 increase in stress around the apex of a notch inch vibration in the readings at a location (Gilbert, 1907, PI. 1) displays the notch. such as that shown in 1819 as compared 10 ft lower than outside of the curtain. During the next 18 yr, most of the remainder with the intensity of stress around an arch Laflamme (1906) recognized clearly that of the 1886 crest was eroded to the present such as the 1966 crest. Hubbard (in "the mighty spouts... ("upwards a hundred arch form which has persisted since then. Philbrick, 1970) demonstrated photoelasti- feet above the crest of the Horseshoe") . . . During the 29 yr between 1875 and 1904, an cally, by the closer spacing of the black are an evidence of extreme mechanical arch crest sharpened into a notch and then fringes around the 1819 notch, that the action, a powerful process of erosion taking broadened into an arch with a recession stress in the 1819 notch was three times as place at the apex of the 'V' . . .," which he ranging from 100 ft on the left of the river to high as around the 1966 arch crest. attributed to a "hydraulic ram effect." I will 200 ft on the right of the river. During the Dow (1921) cited statements by B. Hall in consider them as rock bursts attributable to following 60 yr, 1904-1964, the arch 1827 (1829, p. 202), Lieber (1834, p. 349), extraordinary stress :n the notch resulting retreated a maximum of —150 ft at the and Barlow (1577) about comets and jets of from the rapid relief of the stress, which has center of the Horseshoe and ~50 ft at the water that rose suddenly out of the cloud of been encountered ir. many of the deep site of the old notch. The rate of erosion of mist (especially downstream of the Horse- excavations in rock in the Niagara Falls area the last notch may be as fast as 19 ft per yr shoe) at varying intervals with only a few and which was observed in the unwatered and that of the present arch may reach a minutes between appearances. Hall (1829, American Falls Channel in 1969. Because of maximum of ~2.5 ft per yr. It is reasonable p. 200-202) estimated that they achieved the generally east-west orientation of this to assume that rapid recession is matched by heights of 110 to 120 ft above the stress observed by Bird (in Sbar and Sykes, shallow plunge pools and that slow Maid-of-the-Mist Pool, which is equivalent 1973), those reaches of the river trending recession is matched by deep plunge pools. to —30 ft below the crest of the falls, based generally north will be subjected to greater There is reliable historical evidence for on plotting with a camera lucida. Barlow stress and more rapid erosion of the falls two other notches in the nineteenth century, (1877) stated that the characteristic form of than those reaches trending west, parallel to although neither was recorded by instru- the comets and jets was pointed at the top, the orientation of the stress. mental surveys. One is sketched as a V-notch widening downward; that they reached in 1819 in the survey of the boundary elevations of 1 0 to 30 ft above the crest of Present Slope Stability between Canada and the United States. F. the falls; and that they were accompanied The geologic section at the Horseshoe, by Hall (1818) stated that the Horseshoe "has with a jarring movement of open windows projection from the American Falls (Phil- become an acute angle." Paintings of the and doors in the Clifton House (a hotel) on brick, 1970, Fig. 2), is shown here in Figure falls in the early nineteenth century, and the Canadian side, somewhat over half a 2. The crest is formed by the Lockport reproduced by Dow (1921), generally mile from the Horseshoe. At first reading, Dolomite beneath which lie a series of substantiate this. In particular, Thomas these remarks nade little sense and still are thinner and less durable strata commencing Chambers' Niagara Falls (although uncer- not readily explainable for the American with the Rochester Shale and bottoming in tainly dated "c. 1820-1840" below the Falls but are understandable at the Horse- the Queenston Shale, the plunge-pool rock. reproduction in a Buffalo Academy of Fine shoe when the dates come into perspective. The strata dip upstream but so gently that Arts catalogue, 1964), depicts a striking The early nineteenth-century notch, of 1827 the beds appear horizontal on the walls of V-notch similar to the one in the Boundary and 1834, progressed through a narrow the gorge. Bedding planes and joints Survey of 1819 and startlingly different arch to become a broad arch shown in the separate the rocks into blocks and slabs of from the appearance of the Horseshoe now. 1842 survey. 1877 follows the 1875 survey many sizes, and the stresses in the walls of B. Hall (1830, Etchings, No. 11) recorded by in which a snia'l notch was found in the right the gorge and in the Horseshoe have camera lucida a Horseshoe that was a deep, side of the crest and which by 1886 had produced a series of vertical fractures narrow arch in 1827. Gilbert (1907, Pis. 3 developed into a huge re-entrant, the third parallel to the gorge. The geologic factors nineteenth-century notch. All three dates affecting the rate of recession are those that represent periods during notch or narrow- relate to the stability of a rock slope arch configurations when high stresses composed of this succession of strata, which 1 were present in the face of the rocks In river terminology, left and right refer to a view in a are subjected to a hydrostatic head at the downstream direction. of the Horseshoe. I think these comets or jets foot of the slope at the Maid-of-the-Mist Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 WHAT FUTURE FOR NIAGARA FALLS? 95 Pool of ~ 180 ft, including the surcharge of the thick sheet of falling water at the focus of FUTURE OF NIAGARA FALLS 20 ft of water flowing over the crest. the falls. The debris is ground so fine, even Other forces affecting the stability of by the 25 to 50 percent remainder of the Site of the Recession slope are: common weathering in this cold total flow of the river after diversion, that The future of Niagara Falls will be within country, ice plucking, abrasion by wind the debris is carried off in suspension or the limits of the map (Fig. 1), which extends driven spray, and cavitation. In the special solution by the slow-moving waters of the upstream south from the Rainbow Bridge up case of the Horseshoe Falls, the normally Maid-of-the-Mist Pool. But at the flanks, the the Upper Great Gorge past the American readily weathering, frost- and moisture- big blocks on the shelves may outlast the and Horseshoe Falls to the head of the river susceptible Rochester Shale is somewhat retreating Horseshoe, as can be seen in Lake Erie. The river up which the falls will protected from the effects of variations in immediately downstream of Terrapin Point. recede flows northward in a channel that is temperature and moisture by the constant In 1969, when the American Falls was forced to branch by three islands, important presence of the thick sheet of water falling unwatered, its talus had been barely to this paper. The downstream island is over the cliff. The shale, which weathers to a rounded by its thin sheet of water unless the Goat, above which is Navy Island, and slope of 45° or flatter under atmospheric fragments were under 3 ft in diameter. Thus, farther upstream is Grand Island. Goat conditions, has been seen beneath the at the very slowly retreating American Falls, Island is the smallest and is bordered on the unwatered American Falls on a vertical the blocks from the erosion of the face north or right side by a shallow, narrow slope on sheeting joints parallel to the center accumulate as rising talus and serve to channel. Above Goat Island is a depth of line of the gorge. In airphotos taken in 1966, defend the American Falls from causes of water line of 6 ft, which is about the depth of the focus of the Horseshoe Falls appears to recession. We can conclude that a crest water in the narrow channel. The thalwegs be on a nearly vertical slope; thus it is depth of 5 ft of water falling 110 ft is of the river, and the Chippawa Channel on believed that the classic undercut profile of insufficient to destroy the talus composed of the west or left sides of Navy and Grand the Horseshoe Falls may be in reality a Lockport Dolomite and Rochester Shale Islands and the Tonawanda Channel on the condition that develops along the flanks and produced by the American Falls. We should east or right side of Grand Island, are defined may not occur in the active focus. It is bear this in mind as we predict the behavior by a solid dark line, as is the thalweg on the apparent that the fastest rate of recession of the Horseshoe Falls as it retreats toward east or right side of Navy Island. The main occurs during the notched configuration Lake Erie. channel on the left or south side of Goat when rock bursts result from high stresses in Island is a series of cascades flowing down the rock, as they did several times during the Rate of Retreat in the Past the Lockport Dolomite bedrock side slope nineteenth century. Conversely, the slowest The average rate of retreat through the of an old south-flowing buried valley rate of erosion is during the stable arch 11,000-ft-long reach of the Upper Great (Spencer, 1907, p. 80). The upstream ledge configuration such as has prevailed during Gorge during the present stage of discharge at the head of the rapids is the natural weir the first three quarters of the twentieth of the four upper Great Lakes in the Niagara that establishes the Chippawa-Grass Island century. River may be estimated at 2 to 3 ft per yr if Pool along the lower end of Grand Island. we accept the 4,000- to 5,000-yr estimate of Diversion of water for power production Side-Channel Effects age of the Upper Great Gorge by V. K. Prest has necessitated construction of control The bottom survey by Ontario Hydro of (1972, written commun.). This average rate works to maintain the level of this pool. A the Upper Great Gorge shows in 1969 a is the mean of many rates operating for navigation channel has been excavated from sequence of upstream progressively deepen- unknown periods of time and is hinted at Squaw Island at Buffalo, New York, down ing plunge pools in a single line; but on only by the peculiar profile of the river the Tonawanda Channel beneath the North approaching the American Falls, the bottom bottom. From this bottom it is clear that the Grand Island Bridge on highway 1-190 to the survey shows considerable confusion in the recession of the falls becomes slower with city of Niagara Falls, New York. The river contours, as if there were several plunge time as the plunge pools become deeper with flows in a chute from Lake Erie and pools for each stand of the Horseshoe and as a downward slope of 0.0066 percent in an navigation is passed around the chute if the main current of the river were diverted upstream direction until suddenly, as just through Black Rock Canal and Lock. from the centerline of the valley. It appears downstream of the American Falls, the that where a side-channel stream strikes the bottom rises 80 ft. There a new cycle of Geological Conditions main stream obliquely and pours over the declining rate of recession begins, but this The bed rocks of the site area are shown in flank of the Horseshoe, as occurred when recession seems to be slowing down more the river channels on Figure 1 as if they were the Horseshoe moved upstream past Goat quickly than did the earlier cycle because the exposed at the elevation of the bedrock Island, confusion occurs in the river, and the 0.018 upstream downward slope of the surface, which at some places is deep rate of erosion is affected by the cross flow of thalweg, projected through the bottom of beneath glacial fill in buried valleys and at the side stream. The depth of erosion into the plunge pools, is steeper. other places is reported to be at the thalwegs. the stream bed is shallower than when a The rates of recession published in the The sources from which the map and the single line of plunge pools is eroded; this report of the International Joint Commis- geologic section (Fig. 2) have been compiled need not indicate a faster rate of retreat sion (1953, p. 14) are as follows: are listed in Appendix 1, but the interpreta- because the water may be distributed over a Period Rate (ft per yr) tions shown in these two figures are my broader channel, and the resulting thinner 1842 to 1905-1906 4.2 responsibility. sheet of falling water may be insufficient in 1905-1906 to 1927 3.2 The geological conditions are shown in mass to erode a deep plunge pool in a given 1927 to 1950 2.2 section in Figure 2 from the Horseshoe Falls time interval. Eventually, opposite the The Commission related the slower reces- near the right side to the upstream end of upstream end of Goat Island, the effect of sion to diversion of water for power Niagara River at the north shore of Lake the side stream diminished and a single line production with resulting decrease in head Erie at the left. Note the following: of plunge pools now seems to be present, on the crest of the Horseshoe. I think the 1. The flow of Niagara River is from left leading toward the focus of the Horseshoe. stable arch configuration of the twentieth to right and the recession would be from century had a much greater effect and that right to left (as shown in Fig. 2). Erosion of Talus the higher rate in the initial period was the 2. The depth of the river varies tremen- The forces of erosion produce rock debris result of the last two notch configurations of dously as the result of the type of rock that that falls from the face and is destroyed by the nineteenth century. forms the surface of rock along the channel Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 96 S. S. PHILBRICK and the ancient buried channels that cross upstream. But generally, the water will pour recession of the waterfalls in the same rocks. the Chippawa Channel. The shallowest down the rapids on a stepped slope created Recession will follow :he thalweg, hence the water is between the Horseshoe Falls and by abrasion anc. solution of the soft rocks of importance of the depth of water in Navy Island. the Salina Group and the floating off and predicting the course of the retreating 3. The strata dip uniformly upstream but destruction of its weak constituent slabs. waterfalls. show variable apparent dips in this section, As the top cf the Lockport dips beneath Diversion of approximately 50 percent of which follows the thalweg of the crooked the surface of rock and the Salina appears, the natural flow of the Niagara River for course of the river. the upper part of the valley will cease to be a power purposes since the early 1960s has The strongest, most resistant formation is dolomite cliff and will become a much flatter not caused talus to t uild up in the plunge the Lockport Dolomite. It forms the face and sloped outcrop of the less resistant Salina pool at the focus of t!ie Horseshoe Falls, at crest of the Horseshoe Falls and continues to rocks. As the falls recede upstream, the least as far as aerial photography permits underlie and be the surface of rock in the continued upstream dip of the strata will observation. Thus the present Horseshoe, river, all the way up to the upstream end of lower the base of the Salina and increase the operating at 50 percent of natural flow, is a Navy Island and the midpoint of the north height of the Salina exposure to produce a recessive waterfall. Further reduction as it side of Grand Island. distinctly broader, flatter, cross-sloped occurs during nontourist hours, to approx- Upstream from the upper contact of the gorge quite different in appearance from the imately 25 percent of the natural flow of the Lockport Dolomite, above Navy Island, the underlying Lockport Gorge. This newer Niagara River, seems to be adequate, rocks of the Salina Group form the surface portion of the valley may be called the because again there is no accumulation of rock up to Fort Erie, near the head of the "Salina Gorge" and is outlined on Figure 1 talus at the focus of the Horseshoe Falls. river about half a mile above the Interna- by diagonally striped lines paralleling and Therefore, a combination of 50 percent tional Railway Bridge. There, the river is extending upstream beyond the cross- flow during daylight hours, or tourist flowing practically on the overlying resistant striped lines defining the Lockport Gorge. hours, and 25 percent during nontourist Bertie Dolomite and then on the Onondaga hours has maintained a functioning Limestone, which forms the natural sub- Hydraulics of the Niagara River Horseshoe Falls capable of recession. Its merged weir controlling the level of Lake The recession of the falls will also be rate of recession may be less now than Erie. The Salina Group is divided into the governed by t-.e hydraulics of the Niagara when a full 92 percent was moving over Vernon Formation below and the Syracuse River. Among the important hydraulic the Horseshoe, but it is still an efficient Formation above. The Salina Group is the factors are the quantity of natural and waterfall with 25 percent flow or —50,000 great geologic unknown in speculating on diverted flow, the number of channels, and cfs. Presently, the natural flow in each the retreat of the falls. Most of the the depth of water of the river. The quantity channel upstream of the control structure knowledge of the Salina has been gained of flow in each reach of the river and appears to be at least 30 percent of the total from subsurface studies because the Salina is channel, along which the geo.ogic section is flow of the river or —60,000 cfs. Thus a characterized by lack of outcrop. In the drawn, is shown on Figure 2 as numerals recessive waterfall could function simul- subsurface, the Salina has been subdivided immediately above the water surface. These taneously in the Lockport Dolomite, the into six units, four composed of shale and numerals express the quantity in terms of most resistant rock in the river, in each of the two containing interbedded dolomite and percentage of water entering the river from three channels bordering Navy and Grand shale. All six of these units carry one or more Lake Erie, neglecting such water as may be Islands. But there is not, and apparently soluble evaporites — anhydrite, gypsum, diverted for navigation, water supply, and never has been, sufficient water flowing over and salt. The result is that the Salina is a sanitary usage. Diversion becomes a major the American Falls to make it barely more weak, easily eroded series of rocks except in factor in the behavior of the falls because than a quasi-stationary waterfall, certainly the uppermost unit, the Camillus Shale. nearly 50 percent of the water during not recessive in the sense of the behavior of Certainly the lower five units are not capable daylight and (or) tourist hours and 75 the Horseshoe Falls. I define a quasi- of forming steep slopes because of the percent during nontourist hours is diverted stationary waterfall as one that may recede weakness of anhydrite, gypsum, and salt, to the power entities for the pollution-free slightly but is essentially stationary, an which would probably shear under the production of electric energy. The major almost permanent vertical riser in the weight of the rock in the Horseshoe Falls or diversion for both countries occurs in the thalweg. in the walls of the Upper Great Gorge. Chippawa—Grass Island Pool below Navy The Horseshoe Falls will exist only in the Island. Because the American Falls passes Recession of the Falls Lockport Dolomite. Thus the gorge that will about 8 percent and the Horseshoe Falls Let us examine where the Horseshoe will develop as an extension of the Upper Great passes about 92 percent of the undiverted be at various points in its recession, Gorge, as the falls recede, will be limited to flow and the separation of the channels by configuration, and depth of plunge pools, the Lockport Dolomite. It might well be Goat Island is about at the control structure, and the effect of the position of the called the "Lockport Gorge" and is outlined the section shews 92 percent—D below the Horseshoe on the rest of the river. on Figure 1 by cross-striped lines that extend control structure, which should be read as Event No. 1 (see Fig. 1) occurs when the part way up the Chippawa and Tonawanda 92 percent of total flow minus the quantity Horseshoe reaches the 6-ft water-depth line. Channels. The height of the falls will diverted. At and above Navy Island, the Then the water in the Chippawa-Grass decrease upstream with the decline in figures are percentages of total flow. It is Island Pool will be lowered in elevation to elevation of the top of the Lockport. This net assumed that Navy Island splits the such a point that the American Falls, then at loss in height of the Horseshoe will be met by 60 percent quantity of the Chippawa the cross-striped line a short distance east of development of upstream regressing rapids Channel into two equal flows because of the the present location, will be almost dry. that will extend from the progressively nearly equal size of the two resulting There may be a small quantity of water lowering crest of the receding Horseshoe channels. More satisfactorily measured drifting through the channel at the head of upstream to the top of bedrock beneath the estimates show that Grand Island splits the Goat Island, bur the Horseshoe Falls will river. The slope of the rapids may be affected total river flow into 40 percent to the have captured most of the water that was by the slopes of the valley walls of buried Tonawanda Channel to the east and 60 moving down the American Channel and valleys, which appear to cross beneath the percent to the Chippawa Channel to the over the American Falls. The American falls will have ceased to recede and will become Chippawa Channel; one valley just above west. These differing quantities of flowing dry; the American Falls will be a memory. Navy Island and the other —2 mi farther water will result in differing rates of Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 WHAT FUTURE FOR NIAGARA FALLS? 97 This isn't going to happen immediately. Navy Island, two sources of water approach and become quasi-stationary waterfalls. Assuming that the true twentieth century this Horseshoe, one from the Tonawanda This will occur first in the Chippawa rate of retreat of the Horseshoe (—2 ft per yr) side on the north side of Navy Island, Channel and is noted as Event No. 3 on will continue, then the American Falls have a carrying 70 percent of the flow; 40 percent Figure 1. life of 2,000 yr under natural conditions, but from the Tonawanda Channel; and 30 Event No. 4 is located farther upstream on with the nineteenth century rate, with percent from the right channel around Navy Figure 1 where the Chippawa Channel at notches (4 ft per yr) the life would be about Island. Coming in from the south, on the left the head of Grand Island has intercepted the 1,000 yr. Because of the diversion of water side of Navy Island, is a 30 percent flow of full flow of the Niagara River, 40 percent of for power generation, the life of the the river. There is a potential double-falls which ran down the Tonawanda Channel. Horseshoe will be extended. situation. The major part of the Horseshoe With the interception and the capture of the As the Horseshoe reaches the point of will retreat around Navy Island and head up full flow by the Chippawa Channel, the Navy Island in the deep water, it will have, the Tonawanda Channel. A minor waterfall Tonawanda Horseshoe and the Salina lowered the water surface in the will move back up the left side of Navy Gorge above it will be marooned and will Chippawa-Grass Island Pool by ~8 ft from Island, up the Chippawa Channel. Both stay in the vicinity of Tonawanda as a dry its present elevation. Although the hy- waterfalls will be working in the Lockport gorge taking only whatever local drainage draulics of this action are not clear, it might Dolomite. However, the right one coming in comes in. So there will then be two dry result in lowering the elevation of Lake Erie with 70 percent of the flow will have moved gorges with dry waterfalls, one on the right if that elevation is now dependent as farther upstream and will then be opposite side of Navy Island and one near Tona- headwater of the chute upon the elevation of the mouth of the right channel on the right wanda. The surviving Horseshoe will the Chippawa-Grass Island Pool as tailwa- side of Navy Island. Another double carry the full flow of the Niagara River and ter of the chute at the head of the Niagara waterfall will develop here, with 40 percent will proceed upstream slowly over the Bertie River. This might occur sometime after the of the water coming in from the right (the Dolomite and Onondaga Limestone because unwatering of the American Falls, probaoly Tonawanda Channel) and 30 percent the head on these durable rocks will not be within the next 7,000 yr. coming in from the left, which is the right nearly as great as it is on the present As the Horseshoe Falls retreats up the side of the Chippawa Channel. The Horseshoe and will become, I am sure, very Niagara River, it will climb the Cascades to waterfall splits — one goes up the Tona- similar to a quasi-stationary waterfall. It will gain ~60 ft in height at the summit of the wanda carrying 40 percent of the natural move a little bit, but extremely slowly and Cascades, close to the control structure. All flow, and the other comes up the right side of for all practical purposes this will be the end of this bedrock is Lockport Dolomi;:e. Navy Island carrying 30 percent of the flow. of the recession of the Horseshoe Falls, Beneath the level of the Maid-of-the-Mist There will then be three waterfalls: one on which at last becomes Event No. 5, the Final Pool, the present section of strata will the left and one on the right of Navy Island, Falls. They may move back and lower the continue with only a slight upstream dip and one in the Tonawanda Channel level of Lake Erie but most probably the then because this reach is subparallel to the strike. upstream from Navy Island. The waterfall in lake level will stand for thousands of years. Thus the plunge-pool strata will remain the left channel of Navy Island will have nearly constant while the face of falls will be been moving upstream with 30 percent of CONCLUSION higher and will carry a much greater the flow of the river, but because of its When considering the behavior of the thickness of dolomite than at the present shorter distance of travel will arrive at the Horseshoe Falls in the near or the far future, location. Modern conditions will be accen- head of Navy Island before the one on the it should be remembered that the Niagara tuated by the greater load on the face, and right side of Navy Island arrives there. Here River is controlled by the control structure we should look forward to the repetition of will begin the erosion of the broader and above Goat Island; that 50 percent of the notched configurations interspersed with flatter side-sloped Salina Gorge. Event No. 2 flow of the river is diverted for hydroelectric arched configurations of the Horseshoe. will then occur as the left waterfall captures power all the time; and that during Thus there will be a continuation of the the right channel and the waterfall on the nontourist hours, about 75 percent of the present irregular thalweg marked with highs right side of Navy Island is abandoned. The river is going into storage or through the and lows that decrease in elevation in an conquering Horseshoe will carry 60 percent turbines. The Niagara River is subject to upstream direction. Taking the slope of the of the river and will move smartly up the human control now. In the event of decrease in elevation of the future plunge Chippawa Channel beneath the increasing recession of the Horseshoe, there would pools as a continuation of the present thickness of the easily eroded, less resistant undoubtedly be a move to control the upstream downward slope of 0.018, the shale, anhydrite, salt, gypsum, and dolomite motion, either by actual modification of the greatest depth of plunge pool will be ~ 180 ft of the Vernon and Syracuse Formations of rate of erosion of the Horseshoe itself, which below the surface of the Maid-of-the-Mist the Salina Group. The Tonawanda Horse- is feasible, or by the distribution of water Pool extended upstream and will be located shoe will carry only 40 percent of the natural over the surface, or by the diversion of the at about the position of the control flow of the river and must erode the resistant water into uses that would reduce the structure. Upstream from there, beneath the Lockport Dolomite. The rate of retreat of quantity of water flowing over the Horse- maximum elevation of the dolomite, I have the Chippawa Horseshoe with its much shoe. Certainly a change in the water surface drawn the thalweg (Fig. 2) at about the same greater quantity of water will be faster for in the Chippawa-Grass Island Pool, and elevation on the assumption that 180 ft is so some distance on a rock or material basis as resulting change in water surface in Lake deep as to be near a maximum probable well. As the Chippawa Horseshoe moves Erie, would quickly call for a control depth because it is approximately the depth upstream, the height of the Lockport will structure in the upper end of the Niagara of the elevation 112 plunge pool carved by decrease with the upstream dip of the River. I look at the recession of the the great discharge of the early episode of the formations, and the height of the falls will Horseshoe Falls as something that will not four Upper Great Lakes. With the decrease decrease as well. Stepped rapids will be permitted, because of the great value of in elevation of the Horseshoe on the develop in the thalweg of the Salina Gorge the Niagara River in its present condition. upstream dip of the dolomite, the thalweg above the falls. Eventually Chippawa and The period that Lyell (1830, p. 181) will presumably rise to a depth of ~50 ft at Tonawanda Falls will approach the height considered (30,000 yr), for the retreat of the the quasi-stationary waterfalls as the energy of 50 ft which, I have assumed, will stand for Horseshoe to Lake Erie, or 50,000 yr if we of the lowering waterfall becomes less. a long period of time without retreating assume that this is more probable, is a period To return to the Horseshoe at the point of appreciably. They will cease to be recessive of time more than sufficient to permit a Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021 98 S. S. PHILBRICK radical change in climate in the area of the Ontario (see especially Fig. 44, Structure REFERENCES CITED Niagara River. Less than 12,000 yr ago, ice map on the base cf the Rochester Formation, Barlow, W. H., F.R.S., 1877, Upward jets of stood where the Horseshoe now stands. Are Niagara Peninsula and eastern Lake Erie, Niagara: Jour. Franklin Institute, v. 104, p. we to assume that ice will not return in less southwestern Ontario): Canada Geol. Sur- 275-277. than 30,000 or 50,000 yr? vey Paper 65-30. Chambers, Thomas, 1964, Niagara Falls, a Kreidler, W. 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Service MANUSCRIPT RECEIVED BY THE SOCIETY MARCH Silurian oil and gas fields of southwestern Bull. 404,210 p. 30,1973 Printed in U.S.A. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/1/91/3429339/i0016-7606-85-1-91.pdf by guest on 02 October 2021