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Home , Geography of Manitoba, Glaciofluvial deposits, History of Manitoba, Interlake, Interlake Region, Lake Manitoba

•••••••••••••••••••••••••••••••••••••••••• GEOLOGY AND OF

M. Timothy Corkery

The geological abundant). Each of these eons was the southwest ofthe province and in spans more than 3.5 billion years. hWldreds of millions of years long, the Lowlands, in the By studying the rocks of the prov­ so they are further di vided into northeast. ince, geologists can deduce what the eras: the is divided In south-central Manitoba, rocks landscape ofManitoba was like mil­ into the and Proterozoic, deposited in shallow seas during lions, or hundreds of millions, of and the Phanerozoic is divided into several periods of the are ears ago. At times seas covered the the Paleozoic (the time when early found; these periods are, from old­ whole province; at other times the forms of life existed in the seas and est to youngest, the Ordovician, province was covered by up to 1.5 then spread onto the land); the Silurian, Devonian, and Mississip­ km of . There were volcanic is­ Mesozoic (often called "the age of pian. For the Mesozoic era, we have lands in the area that is now Flin reptiles"); and the Cenozoic (the rocks deposited during the . Flon, and two continents collided in time when warm-blooded animals and periods, and in the Thompson area. Rocks can re­ - mammals - became dominant) some locations these are overlain by veal whether it was warm or cold (Table 2 .1). The Phanerozoi c eras Cenozoic rocks from the pe­ and indicate when our province was are further subdivided into periods. riod. Of most recent origin are gla­ close to the equator. Also, by study­ Manitoba's geological history is so cial sediments from the Quaternary ing fossils we can even deduce rich that much of the geological period that cover much of the prov-­ something about the animals that time scale is represented in our inee. lived here long before there were rocks. people. The rocks and that HISTORY IN Geologists partition the history formed at different times in the past THE RECORD of the earth in the same way that occur in different places throughout historians subdivide and name dif­ the province (Figure 2.1). The oldest Precambrian fe rent periods of human history, rocks in Manitoba were formed dur­ Rocks in the Precambrian Shield such as the Bronze Age and the ing the Precambrian eon, and are are predominantly igneous in origin Renaissance. In the earth's history, exposed in the Precambrian Shield but include areas of metamor­ the two major time divisions, that stretches from southeastern phosed volcanic and sedimentary termed eons, are the Precambrian Manitoba northwestward to Sas­ rocks called greenstone belts. Broad (the time when there was little liv­ katchewan and the Northwest Ter­ reas of igneous rocks were formed ing) and the Phanerozoic (the time ritories. Younger sedimentary rocks by the cooling and crystallization of when evidence suggests life was of the Phanerozoic eon are fo und in extremely hot melted rock material 12 THE call ed m agma. After the old rocks of Table 2.1 Geological Formations ofManiLoba the Precambrian Shield were formed, AGE' ERA PERIOD EPOCH FO~ MATlON n«'. 8ASIC lrTHOlOGY MEMBE R 'I they were buried deeply in the earth C QUATER· ..;fa}'T Tot> soil dun asand• E NARY and chang d by heat and pressure .J,r,g')t;(;F.IE N GLACL'.L DRIFT 140 , , gravel. 1J1der ~.a l to metamorphic rocks. However, 0 Z ~():£I,'( this expla nation is over implified; ~ 'lC .,.:. 0 t.1~·fl' TERl IAAY the rocks are able to tell us more 50 I t :.cFl,;,r C p'lf(Wj[ TURTl£ MTN . 120 Shale. clav and saM LI(tOile b. d. - localed onl In TUllia MDunla! about the distant past. They tell of OS continents olliding, volcanoes erupt­ BOISSEVAlN 30 Sanaand saMSIOns, glO

zoic and created a chain of moun­ W01LAl1TOM / IIEJAHILIHI tains. Again the rocks were melted il ! Tb .. I and metamorphosed during another SEAL Tl mountain-building event, called the .. / Trans-Hudson Orogeny, which closed / ; the Precambrian eon in Manitoba. Th e geological cycle of continen­ tal rifting and ocean floor spread­ CHIPEWYAH Tb ing, closure of th e ocean basin by of the oceanic plate, and continental collision concurrent with a mou ntain-building event has been repeated many times throughout tYNNlAK~ geologi cal history. It has now come to 1 Lynn· TV, lEAF RAPID S ' TO be known as the Wilson Cycle, after the famous geologist J . 1 -t,lIPEIUOR ~ 'TI (- -_ DillI. Tuzo Wilson, whose pioneering II. ISSEYNEW , 0..., Ta Thom~SDn PIKWITO NfL Y STU work led to the theory of plate tec­ • Sb . ~.:r tonics. ' # cf GODS Phanerozoic LAKE Sg By th e beginning of the Phanerozoic t eon, the area th a t is now Manitoba N had been eroded down to a rela­ MO l SO~ LAkE • Sb A tively flat to undulating peneplain ___~ =~'00 (almost a ) located in the cen ­ IS LAND km tre of the continent. Sediments de­ f LA KE Sg posited since then have not been dist urbed except by periods of ero­ sion when the land was above sea CE NOZOIC • Tertiary level, because Manitoba, unlike the BERENS III VEIl Cretaceous mountainous areas of and Sb D MESOZOIC , has not been dis­ { Jurassic turbed by a more recent orogeny. This h as resulted in the preserva­ .. Devonian tion of abundant fossils and sedi­ UCHI ",.oW'C Silurian ment a.ry features in the rocks of the Sg j Paleozoic era. Ordovician .. All the younger (Phanerozoic) PRE CAMBRIAN • Precambrian rocks in Man itoba are sedimentary. •T Trans· Hudson Orogen Th er e are two types of sedimentary S Supenor Provlnc:e rocks: clastic rocks and chemical Major su bdivIsions of the rocks. A cl astic rock is formed when .. Pre<:ambri an In Manlloba: an older rock is (1) broken into frag­ Batnolithic granrie ment.s, (2) transported by water or Sedimental)' gne.ss greenstone air, (3) deposited to form a sediment such as a beach sand, and then (4) Figure 2.1 Generalized Geology ofMa nitoba (Source: Modified from Geologi cal Highway • Map of Manitoba 1994, 2nd ed. /Winnipeg: Manitoba Minerals Division, 1994J) lithified (made into a solid rock), typically by cementation. Clastic velopment, and sedimentation b~­ bein g formed in the basin. DUling rocks are widespread in southwest­ gan agam . thjs time th e FUn Flon , , ern Manitoba. Th e famous Thompson Nickel and Th ompson ore deposits were A chemical rock forms by precipi­ Belt was fo rming along the west formed. tation of atoms or mol ecules from a coast of the Superior Continent. As in the Archean, pressures solution with in a n ocean or lake.

~ The sands ofth e day were sitting on built up and another old Archean This can occur wh en organisms the and of the continent to the northwest drifted such as coral or clams make their worn-down mountains from the towards the Supelior Cr at on. In the shell s; alternatively, if too much ofa Kenoran time about 600 million same way that ran into certain substan ce is dissolved in years before. Out in the seas to the and pushed up the Himalayas, the the solu tion, it precipitates to for m west, deposits of mu d and sand Hearne-Rae Craton squeezed the a rock. Chemical rocks a re abun­ were building up on the bottom, and sediments, volcan ics, and ore de­ dant in the Manitoba Lowlands of .. new chains of volcanic islan ds were posits formed during the P rotero­ south -central Manitoba and in the 14 THE GEOGRAPHY OF MANITOBA

T" ~I. ERA A Mo unl.ll n

Wlnnlpe~ Ri ver AI Red Allier

E c

1001)

Honzontal Scale o 50 .. km l raadM 1500 , A 1­ ~------+ -----

Figure 2.2 Geulogical Cross·section of (Source: Modified from Geological Highway Map of Manitoba 1994, 2nd ed. (Winnipeg: Manitoba Minerals Diu isin l1 , 19 47)

Hudson Bay Lowlands. earth's crust known as sedimentary stone for cement; ubsurface deposits Manitoba has rocks from most basins, two of which influenced of salt and potash are potential prod­ periods in the Phanerozoic eon (Fig­ sedimentation in Manitoba: the ucls (Chapter 16). In addition, some ure 2.2), but there are some gaps. Hudson Bay Basin centred in Hud­ of the rocks serve as reservoirs for F r instance, there are no rocks son Bay, and the Willi ton Basin, petroleum. from the Penn sylvanian, Permian, centred in northwestern North Da­ At this t ime Manitoba was at a or periods, nor are there kota. tropical latitude, c vered by warm, any from the Upper Jurassic. Dur­ The Williston Basin developed shallow seas that teemed wi th newly ing these imes all of Manitoba was fyo m the south as the seas advanced developing life. As a result, numer­ above as it is today, and as over the slowly subsiding Precam­ ous fo ssils such as corals, trilobites, now, the rocks that were deposited brian Shield. This advance of the and brachiopods are found in Pa­ during the previous periods were sea, termed a transgression, left de­ leozoic rocks. It was during this era eroded by river and wind a tivity. posits of sand t ne (dominated by that an explosion of li fe for ms oc­ Thus during these times, not only the quartz-rich andstone of the curred. However, this does not indi­ were no new sedimentary rocks de­ Winnipeg Formation) as it flooded cate that li ~ began in the early posited in our geological record but northward (Table 2.1). As the Pre­ Paleozoic, but rat.her that a wide ar­ we were actually losing pieces of the cambrian Shield continued to sub­ ray of animals evolved hard parts record. When a new sh Bow cratonic side, sediments accumulated on the that could be preserved as fo ssils. It sea again covered the central part of shallow bott.om of the ancient sea at is an unanswered questi n why the during t.he J urassic a rate that kept pace with the sink­ sudden explosion of these life forms period, the sedimentary record re­ ing of the crust below. These occ uned t this time. sumed, with he sediments being sediments formed the dolomites, P al ozoic rocks in Manitoba con­ deposited on the eroded surface of limestones, and interbedded shales tain representatives of all the major the older Paleozoic strata. This type of the Red River Formation. The phyla of the animal kingdom (Table of contact is called an unconformity rocks dip gently t wards the centre 2.2). A partial list of fossils from the (Figure 2.2 . ofthe basin in , where Stony Mountain Formation (Ordo­ subsidence was gre test (Figure vi cian) includes several kinds of Paleozoic 2.2). The Paleozoic rocks of the coral, snails, brachiopod , crinoids, Paleozoic sedimentary rocks cover Williston Basin contribute to Mani­ sponges, trilobites, nautiloid cepha­ the Precambrian Shield in the Hud­ toba's industry through lopods, and even some of the earli­ son Bay Lowlands and in south­ produ ts such as silica sand, dolo­ est armoured fishes. western Manitoba. These rocks ac­ mitic limestone fo r building stone, cumulated in depressed areas in the dolomite, and high-calcium lime­ Geology and .,> ofManitoba 15

Table 2.2 Major Phyl a of the Animal Ki ngdom

Phylum Animals Included

Porifera Sponges

oelenterata Corals, sea anemones

Mollusca Clams, snails, squid

Annelida Wor ms of all shapes and sizes

Arthropoda Trilobites (extinct), crustaceans (crabs, crayfish, shrimp, bamacles), insects, chelicerates (spiders, scorpions, ticks, mi tes) • Echinod ermata Starfish. sea cucumbers. sand dolJ arf! , sea urchins. crinoids Chordata Al most all ani mals with a backbone (fish, amphibians. dinosaurs. reptiles, birds, mammals)

Mesozoic been fou nd in the predominantl toises and alligators, which could At the conclusion of the Paleozoic marine strata .in Manitoba, the not survive extended periods of cold • era, t he marine sedimentary rocks rocks of equivalent age to the west weather, indicates a warm climate. were raised above sea level and have abundant dinosaur remains. Carnivores such as sabre-toothed eroded. This erosional surface was There is still a possibility of finding cats, bears, dogs, and small weasels characterized by the development fossil dinosaurs in Man itoba, in the found no lack of food on these of sinkholes and caves in limestone, eastern margins of the deltaic sys­ grassy . Even an unusual sa and by the development of and tems of rivers flowing from the bre-toothed deer found a niche in valleys. Later, downward move­ mountains to the west. the environment. ment of the earth's crust led to a re­ As the climate ch anged with ap­ turn of shallow seas and to the accu­ Cenozoic proach ofthe , so did the ani­ mulation of Mesozoic sediments on Only a small portion of Manitoba mal life. Woolly mammoth, bison, the erosional surface. The contact contains rocks of early Cenozoic and other cold-tolerant species took between the eroded Paleozoic rocks time, which began about 64 million the place of the savanna-dwelling and the base of the Mesozoic rocks years ago. strata of the populations. Possibly the latter is another example of an uncon­ Turtle Mountain Formation are were finally driven to extinction as formity. Mesozoic sediments, which lilnited to a relatively small isolated colder winters and dry conditions formed red siltstones, sandstones, area capping the topographic high reduced their range. shales, and gypsum, were deposited of 'furtle Mountain, in southwest­ in ancient seas that covered Mani­ ern Manitoba. These strata, con­ PREGLACIAL TOPOGRAPHY toba from about 64 to 225 million sisting primarily of fi ne sandy and AND DRAINAGE • years ago. Distant volcanic activity, silty shales, rest directly on Mes­ probably in western North America, ozoic rocks. The land was uplifted about 50 mil­ spread volcan ic ash, which was The past 55 million years has lion years ago, and the Mesozoic later altered to beds of bentonite, been a time of relative geological seas retreated from Manitoba; even across Manitoba. Gypsum, bento­ stability in central North America. Hudson Bay may have been el­ nite, brick cl ay, and shale are im­ The region was uplifted from the evated above sea level. This newly portant mineral products from the sea and became a fl at plain. There exposed, generally fi at former sea­ rock fo rmations of the Mesozoic era was little sedimentation, and ero­ floor was subjected to erosion by riv­ (Chapter 16). sional patterns began to develop on ers. Erosional patterns that persist With the return of the shallow the plains. Animal life became di­ today began to develop on the thick seas, most of the species that had verse and abundant; paleonto­ Cretaceous shales th at covered previously lived in the region re­ logical digs in 10-milljon-year-old most of southern Manitoba 55 mil­ turned, with some noteworthy ex­ sediments in the central plains of lion years ago. The land then, as ceptions; fo r example, trilobites and the indicate that doz­ now, sloped away to the east from graptolites, which would have done ens of hoofed species, similar to the Rocky Mountains, and rivers well in a similar environment, were those found in t he African plains of fl owed eastward across the Prai­ extinct by this time. However, fos­ today, were present. Gr azing ani­ ries, down this gentle slope towards sils of large marine vertebrates, mals such as horses, pronghorns, the (Figure 2.3). such as mosasaurs and plesiosaurs, and camels occupied the grass­ Some were diverted northward into • are foun d in Mesozoic strata. This lands, which they shared with vari­ the Mackenzie watershed, others was the age of reptiles, and al­ eties of elephant, rhinoceros, and south to the Mississippi watershed, • tho ugh fossils ofdinosaurs have not tapir. The presence of fossil tor­ and possibly some flowed across the 16 THE GEOGRAPHY OF MANITOBA Shield to drain to the al'ea where Hud on Bay is today, NORr~W [ ll m ilT 11[1 H is diffi cult Lo locate these an­ Preglacial cient river and stream valleys be­ Channel cause they have been deeply buried beneath glacial deposits, but they had 50 million years t erode the Mesozo ic sh les that may have x­ tended as far east a the On tario border.2 Before the onset of glad ­ bon , the shales were eroded back to the Manitoba , and the eastward-flowing streams carved deep valJ eys, producing the em­ b yments in the escarpment that ", are now occupied by the Assini­ boine, the River, and the Swan River.

The Manitoba E scarpment is, 6111i!ff then, a preglacial feature. It was ("OWMBlj not significantly eroded by glacia­ tion be ause of the ero 'ion-resist­ ant na ture of the overlying hard gray Odanah shale. This shale, with its high silica cont n t derived from and the remains of sili­ ceous microorganisms, formed a re­ MONU~i sistant caprock to the Manitoba Es­ FIgure 2 ..'3 Preglacial Drainage of the Prairies (Source: Modified from J .B. Bird, The carpmen and prevented it from be­ Natural Landscapes of CanHdl'! (Toronto: Wiley Publishers of , 1972j, 117) ing reduced to the level of centr a1 and east rn Manitoba. The escarp­ ditions are so cold that continental When he climate changes again ment generally forms the eastern­ expan d thousands of kilo­ and w rms enough so that the win­ most edge of Cretaceous rocks in metres from high latit udes, and al­ ter addition of ice is less than the the province. pine glaciers build up and flo w summer reduction, the slow­ down from the mountain. This ly stops advancing and the edges GLACIATION happens when the annual addition melt away faster than the i e can of winter snow is greater than the flow. Glacial P eriods melt ing or subli mation in the sum­ At this point the glacier is said to Period of glaciation are not re­ mer. Even small amounts of annual be receding; as the weight of the stricted to the time we call the lee addition of now, which t urns to ice, glacier is removed, t he lands rise Age. During the 4. 5-biIlion-year m build up over h usands of back to their equilibrium position history of the earth, global climatic years. The resulting ice, which in by a process called isostatic reo conditions h ave changed many our area is estim ted to have been bound. This rebound is fa st at first tim s; indeed, major fluctuations s much as 3 km thick over Hudson and then slows. It is not complete are the norm rather than the excep­ Bay and possibly 2 k.m thick over even today, and in the area of tion. While Manitoba was basking Winnipeg will try to fo rm a level Churchill the r ate of rise is still in the sunny conditions and warm surface just as water seeks the low­ about 70 em per century. seas of the Paleozoic era, other con­ st point as gravity pulls it d wn­ As the ice advances over the tinents, such as Africa and South ward, Thus, as the ice thickens by ground, it picks up loose gravel and America, experi enced repeated gla­ annual addition of snow, th e mar­ soil, which are then frozen into its cial periods. This reflects the global gins are pu hed from behind and base, prodUCing an effective abra­ position of tl continent as they th e ice advances as the glacier flows i e as the moving ice erodes and were moved by pi te dur­ to reach an equilibrium. reshapes the land below. Glacially ing these times. However, proxi mity As well as spreading out over the polished outcrops wi th straight to the earth's polar regions did no t land surface, the immense weight of grooves called striations or cres­ always mean ice nd cold; th re is ice de'presses the earth's crust; as cent-shaped "fr actures called chatter evidence of grea forests similar to the ensity of ice i about one-third marks are one result of th move­ those on the we i coast of Canada that of the rocks, it is estim ted ment of the debris-laden ice over near the Nort h Pole during Mes­ that 3 m of ice will depress the earth the rocks. ozoic times, indicating a global about 1 m. So in the regi n f Hud­ Eroded material that is picked warm spelL son Bay, the earth's crust may have up by the glacier is transpor ted and During a glacia ion, climatic con- been depres ed by as much as 1,000 m. 1ater deposited as , an unsorted, Geology and Landforms ofManitoba 17 unlayered mass of debris. Water ing and etching took the fo rm of marks the eastern end of the from the melting glacier also de­ striations and gouges on a small Brandon Hills. G But perhaps the posits sediments known as outwash scale, and the larger north-south best known is that at Bird deposits, and still other materials and northwest-southeast flutings in , 16 km northeast of Winnipeg. are deposited along the shores and the Westlake and regi ons. Here a rugh , narrow ridge of sand on the floors of glacially dammed Over the rest ofsouthern Manitoba, and gravel extends 6.51m1 east from . evidence of glacial erosion is largely Birds Hill and then merges into a During the last several million absent, or at least hidden by glacial delta-shaped plateau that extends years of the epoch , Eu­ . However, at one over a broad area underlying Birds rope, Asia, North America, and An t­ ice fl owing from the Hudson Bay re­ Hill Park. The esker is the main ardica have been in a relatively gion may have been blocked by the source of aggregate material for the cold period - often so cold that vast Mani toba Escarpment.3 As this ice of Winn ipeg. areas were covered by repeated ad­ was channelled to the southeast, it End are thought to vances of the continental ice sheets. may have scoured the edge of the have been deposited at the edge of Studies indicate that there have escarpmen t.. ice sheets when forward motion bal· been numerous periods of glacia­ anced wastage. No fewer than 17 tion, each lasting thousands of Glacial Deposition , have been mapped throughout the years, the most recent of which, Much of Manitoba is covered by gla­ province, although t.he best known termed the Wisconsinan, began cial, glaciofluvial, and glaciolacus­ are in southern Manitoba. Io The about 75,000 years ago and ended trine deposits, although especially Darl ingford extends from about 8,000 years ago. in the southeast, east, and parts of north of Brandon through the Ice sheets did not continuousl the north, bedrock is exposed at the Brandon Hills to the Tiger Hills and cover all of Canada during this time surface. Till and glaciofluvial depos­ east to Pembina Mountain. Further but fluctuated north to the Arctic its are widespread, as are many of north, moraine exLends and south into the United States as the landforms commonly associated south from near The Pas, then east­ the climate varied. Ice from the last with deposition by a major .. ward between and Lake glaciation receded about 7,000­ Hummocky stagnation moraine4 , and on to form Long 8,000 years ago, after a 15,000-ycar (ground moraine) covers large parts Point in (Figure 2.4). period of continually moving glacial of Turtle Mountain, Riding Moun­ Glaci ofluvial outwash sediments ice. The erosion and deposition from tain, Duck Mountain, and the Por­ deposited by glacial meltwater are these episodes of glaciation and the cupine Hills. In the area between also extensive. They give rise to flat significant sedimentary deposits Deloraine and in the terrain on which former outwash formed by meltwater as the glacier southwest, this ground moraine has stream courses can often be seen in continued their slow 3,500-year a distinctive circular ridge pattern, air photographs, such as in the area process of melting and retreat are whereas further east, particulary between Pil ot Mound and Crystal responsible for most of Manitoba's northwest of Killarney, low till City. present-day landscape. ridges 1.5-6 m high trend northeast to southwest. Glacial Lakes Results of Glaciation Classic "inverted-spoon-shaped" Some of the most distinctive scen­ The effects of the glaciation of are not common in south­ ry of Manitoba results from the Manitoba can be grouped under ern Manitoba, but rock-cored stream­ fact that glacial lakes existed in the fo ur headings: glacial erosion, gla­ line hills have been mapped in the area at the end of the Wisconsinan. cial deposition, creation of glacial Holland!'I\-ehernelNoire Dame de Evidence for the existence of these lakes and the alteration of the Lourdes area,5 and dr umlins and lakes takes fOUl' forms: st.randlines, drainage system, and the results of drumlinlike ridges have been map­ which mat'k former lakeshores; isostatic depression and rebound. ped in the area between spillways, which carried water from and Russel 1. 6 Similar features are one to another; deltas, Glacial Erosion widespread throughout northern where rivers entered the lakes and The preglacial topography of Mani­ Manitoba. deposited sediments; and lake bot­ toba was devoid of high mountains and complexes are tom sediments, deposited beyond and deep valleys; consequently, the also abundant in both the north and the immediate shores ofthe lakes. potential for alpine glaciation pro­ the south. Numerous small eskers , the largest of the ducing spectacular landforms such were mapped by Elson 7 in the area lakes, probably came into existence as in the mountains of Alberta and south and west of Baldur and in the about 13,000 B.P. as the result of the British Columbia did not exist. Nev­ area between Cartwright and Crystal merging of a number of smaller ertheless, glacial erosion played a City, and by Klassen8 east of the lakes (Figure 2 .5 ),11 It owed its ex­ role in the evolution of the land­ River southwest of istence to ice damming the north­ scape of Manitoba, part icularly of Birtle. The Arrow Hills, a promi­ ward-flowing, preglacial drainage. the north. Here the ice scraped off nent landform rising 50 m above With various advances and retreats the surface materials, leaving be­ the surrounding landscape north­ of the ice, the lake rose and fe ll so hind extensive exposures of bedrock west of Oak Lake, are probably an that a t different times it emptied once the ice melted. Glacial scour­ esker. A prominent esker also south into the Mississippi system, 18 THE GEOGRAPHY OF MANITOBA east in to the Gl'eat Lakes system, and northwest into the Mackenzie N 12 A system. Finally the pres nt out! t ~ I to the north a long the became availabl , leaving Lake Winnipeg, Winnipeg sis, and Mani­ toba as remnant s of the former gla­ ..", , HUDWIN ~ ~ ~~~~ cial lake (Figure 1.1.1 on page 6). Other named glacial lakes were Lake Sour is and Lake Hind in , southwestern Manitoba. Humm ockY Ground] When it was at its highest, Lake Moraine Agas iz extended far into the A.qsini­ _ End Morain e b in' embayment, and strandlines .L...L Escarpment were formed al ng the Manitoba Es­ carpment. Beaches of this stage, known as the Herman, are found along the east side of Pembina Mountain and Riding Mountain. At a lat r date the lake tood at the Up­ per Campbell level, during which time a prominent beach was formed . ' that extends from the United St Les ," border nor1.h we. t along the Mani­ '. \ toba Escarpment to the Saskatch­ ~ ewan border. Known as the Arden ~ Ridge in the area, it deter­ mines the southeast-northwe t di­ • " MILHER RIDGE· : rection of Highway 352 in thi . area, Winnipeg BEDFOR D HILLS , RED RIVER and is also followed by High ay 10 VAll£Y '.:' . • u,k,"f' further north . '<' S",nbac ~ The steep-sided, flat-floored spill­ ""':::. "It' \\ runb ways are a second piece of eviden e .tt. for the form er exi.stence of glacial lake . They are occupied by rivers that are mi fits, £lowing in valleys Figure 2.4 Major Glacial Depositional Features o!'SoutheTll Manito ba (Source: Modi fi ed far loo large for the present dis­ (rom Geol ogical Highway Map of Manitoba 1994, 2nd ed. (Winnipeg: Manitoba Mineral,; charge. The Assiniboine Valley west Divi8wn, 1994jJ ofBrandon is one example, as is the Qu'Appell e Valley, which joins the A s iniboine near St. Lazare. These km, and has a maximum width ited in summer, when the lake was valley provide a start ling contrast from north to south of 75 km. The open, and the fi ne-grained layers to the general flatness of the 'Ul'­ bulk of the sediments in the delta accumulating in quiet conditions rounding prairies. They were cre­ entered Lake Agassiz by way of the during the win t.er, when the lake ated, possibly in a very short period, Assiniboine/Qu'AppelJe system. IS was frozen. by glacial meltwater fl owing from The fi nal piece ofevidence for the one glacial lake to another.13 In the glacial lakes is the existence oflake­ Isostatic Depression and Rebound south, the Souris and Pembin a riv­ floor ediments, principally fin e The weight of the ice caused depres­ ers occupy spillways for mllch of a nd, silt, and clay, which cover sion of the earth's crust, which re­ heir length. parts of Manitoba and gi ve rise to bounded towards its former position Deltas were deposited into the fl at ten·ain. eposition into Lake once the ice melted. Depression and glacial lakes. Elson lists 33 deltas Agassiz produced the excessively subsequent rebound was greatest deposited into Lake Agassiz, the flat land around Winnipeg, north of where the ice was thickest. In north­ largest of which is the massive POI' age la Prairie, and around Dau­ ern Manitoba the Hudson Bay Low­ Assiniboine Delt a .14 A broad pre­ phin and Swan River. Much of the lands were depressed relative to sea glacial embayment in the M nitoba sedimentation is in the form of level, resulting in a transgression of Escarpment was invaded by glacial varved clays, sediments display'ng th sea (called the as LakeAga siz, and here a delta, with regular alternations ofthin lamina­ far inland as 200 km from the its apex near what is now Brandon, tions nd somewhat thicker layers. present shore of Hudson Bay. was deposited. The delta extends The alternations may represent Strandlines formed along the ea tward almost to Portage la PI' i­ sea onal deposiLion , with the shore and have ince been elevated rie, a distance of a pproximately 120 coarse-grained layers being depos­ to heights a much as 183 m above Geology and Landforms ofManitoba 19

they occupy. Meander development , and abandonment is rapid; the :/ ---. Hudsoll Assiniboine has created 26 cutoffS (,' r ,"­ in the area between the Shellmouth n-'" I -­ ,,",,: 1 ,-­ Dam and Portage 1a Prairie in the Bay hundred years since the first maps .j,",; ';L­ ofihe area were made. Another development has been the dissec\,ion of lhe Mani­ toba Escarpment by small creek ..l draining to the Manitoba Lowlands. +r In the Riding Mountain area, "the escarpment slope region is . .. char­ MANITOBA acterized by deeply incised inter­ mittent streams. Stream incision of between 30 m and 60 mare com­ / , mon."lh At the base of the escarp­ ment, deposition of eroded shale has produced a series of low-angle alluvial fans. Fans of similar origin

~. " occur where small streams flowing from Pembina Mountain reach the lowlands between Morden and Rathwall A prominent feature of the land- , cape of southern Manitoba are ----­ sand dunes developed on lake­ Lake Agassiz Basin '-' ,- . __I deposited sediments and on ouL­ Basin DAKOTA wash. Most marked are those on the Major Lake Agassiz Sedimentation Basin sands of the Assinihoine Delta, _ Tyrrell Sea Sediment "" ­-. - - - ­ - which, north oftheAssiniboine River, have been blown into dunes ofvarious ...... Outlet - - - ­ < '.:..! , (). 100 200 types. Some, southwest of Epinette 122 Elevation of th e Manne '1/ Limit ,"l melTBS) ; Creek, are long, seif-like dunes that ~ . trend northwest-southeast. These ... - - -­ are nOw stabilized by a discontinuous cover of vegetation, but in the Bald Figure 2.5 The Extent of Glacial La ke Agassiz (Source: E. Nielsen et 01 . Surfi cial Geological Head Hills is an area of active Map of Manitoba [Winnipeg: Prouincp of Manitoba , Department ofE nergy and Mines, 19877J dunes with arcuate plans, steep southeast faces, and gentle north­ sea level on the Manitoba- North­ Nelson River into Hudson Bay. Sev­ west slopes19 (Figure 4.1.2 on page west Territories border. 16 Further eral rivers of soulhern Manitoba 57). Although the area of active south, the Agassiz strandlines were have changed course during post­ dunes has decreased during th tilted up to the north; for example, glacial time. Perhaps the most re­ past 20 years, it has been calculated Herman beaches are found at eleva­ markable is the Souris, which once that the dunes are moving south­ tions of 389 m above sea level west flowed southeast in the direction eastward at a rate of 20 em a year. 20 of Morden but rise to 410 m above now followed by the Pembina, but Other, less well-known dune areas sea level west of NeepawaY Also, which now takes a sharp turn to the are the Laude)' Sand Hills on sand the upper Assiniboine Delta slopes northeast to join the Assiniboine deposited into Lake Hind, and an down to the south as a result of (Figure 2.6). The bend is explained area west of St. Lazare developed isostatic rebound, so that the mod­ as an elbow of capture, the former on glaciofluvial sands. ern Assiniboine fl ows along it Souris having been captured by a southern edge. tributary of the Assiniboine. Below PRESENT-DAY the elbow, the Souris flows in a se­ TOPOGRAPHY HOLOCENE ries of incised meanders best seen DEVELOPMENT at the village of Wawanesa (Figure Manitoba can be divided int.o four 2. 7). physiographic regions (Figure 2.8) With the northwar d retreat of the In addition, the misfit rivers of each of which shows the effects of ice front, the drainage pattern of southern Manitoba - the Assini­ Pleistocene glaciation. Manitoba gradually evolved to the boine, the Souris, and the Pembina present situation, in which the - have adopted a meandering form main flow is to the n orth via the on the floor of the spillways that The Hudson Bay Lowlands consist

.­ 20 THE GEOGRAPHY OF MANITOBA

N A G_~

ftl,t ( ~(I~ c,5 ~ Waw~ne$ a

/

•Mill oarei

_ End Moraine

- - 6811'11.6 01 G l iFI.~I.Q J -- Lako Spillway

Figure 2.6 The Souris Elbow o{Capture of an undulating plain oflow eleva­ tion. South of th Churchill River, limestone till covers Paleozoic strata, whereas in the north of the region it overlies the Precambrian. The whole area is overlain by ma­ rine cl ays. In this region oflittle re­ lief, the major el ements of relief are strandlines, fo rmer positions of the Figure 2.7 Inci::;ed Meander and an Abandoned Meander ofthe at Wawanesa Tyrrell Sea shore. Ad ditional relief (Photograph: National Air Photo Library [NAPL] A16404·15; features are the valleys of the Churchill and Nelson ri ers, both of which have cut through the till and in­ Precambrian Shield is hilly, with (Case Study LIon page 6). South of to b drock. Erosion by the contin ntal rock outcrops and numerous glacial Manitoba's , bedrock is ice sheet deranged the drainage, re­ landforms such as eskers and mo­ deeply buried beneath the silty sulting in a maze of swamps, lakes, raine ridges. The region is covered cl ays of Lake Agassiz that form one and st.reams. The region is still rising by the great expanse of boreal fo rest of the fl attest and most prosperous because of isostatic rebound. On 1 and thousands oflakes and rivers. farming areas in Canada. In the Jul 1757, Samuel Hearne, a Hud­ to the north, topog­ son's Bay Company explorer, carved Manitoba Lowlands raphy is more bedrock-controlled, his name and the year into quartz­ The Manitoba Lowlands are the with lim stone outcrops forming ites while si ting by a mooring ring fl attest part of the province, relief plateaus, rarely more t han 30 m on the shor of Hudson B y. Today being generally less than 8 m. The high, often covered by a t.hin layer of thi ring is s veral metres above the lowlands are located south west of glacial deposit, . Here the lowland is highest tide levels. the Precambrian Shield nd are fo rest d and has extensive areas of bounded on the west by the Mani­ muskeg and string bogs. Precambrian Shield toba Escar pment (Figure 2.9) . The Throughout most of th region, The Precambrian Shield is the larg­ region is developed primarily on there are sca"tered moraine as est phy iographic region, an area of gently dipping Paleozoic limestone well as beach ridges of former Lake uneven or hummocky terrain. The and dolomite strata, and has been Agassiz. The has central part of the Shield is occu­ modifi ed by glacial erosion and cut a channel through the sands of pied by the Nelson depression or mantled by glacial deposits. Ie is the Assiniboine Delta, and is one of trough, which slopes towards Hud­ drained by the , Red, many entrenched streams that dis­ son B y and is drained by the and lower Assiniboine rivers, which sect the region. The top of the Churchill, Nelson, nd Hayes riv­ cut across the structure of the un­ Assiniboine Delta has been wind­ ers. Local relief is created by lakes derlying strata_ blown t.o form extensive sand dunes and rivers that are generally en­ Of note in this region are Lakes that re part ially fixed by vegeta· trenched by 15 to 30 m. In north­ Winnipeg, Winnipegosis, and Mani­ tion (Case Study 4.1 on page 56) . In western Manitoba the surface ofthe toba, all remnants of Lake Agas iz the extreme southeast, towards Geology and Landforms of Manitoba 21

Southwest Uplands 1 A Precambrian Shield 3A Porcupine Hills r '\ 3B Swan River Plain 3C Duck Mounlain Manitoba Lowlands 3D Val ley River Plain \ 3E Ri ding Mountain 2A Interlake-Wesllake Plain 3F Minnedosa-Reslon I.~ 2B Red River Pla m 3G Upper Asslniboine Delta 2C Lower Assiniboine Delta 3H Souris Plain 20 Soulheast SeeMn 31 Tiger Hills 3J Pembina Mounioin 3K Boissevain Ti ll Plain 3L Turlle Mountain

~~ km

Hudson Say Lowlands __ Precambllan lA 1- Shield Man.toba Ltlw'ands Soulhwesl • Uplands Sel kirk ~ o_~ , oo 28 __

Figure 2.8 Physiographic R egions of Manitoba .W ' '' '~'' . "' . 20 j, ;; Siernbach I , sandy morainic ~ I deposits impart variable relief and '-­ ";1 ______-;,_( i drainage, and large areas are peat _~ 3K bogs and swamp. 3l ­ t

Southwest Uplands Figure 2. 9 Physiographic Regions 0/ Southern Manitoba (Source: After TR. Wei r, ed., The Southwest Uplands fo rm the Economic Atlas of Manitoba [Winnipeg: Province ofManitoba, Department of l nrlll.~ try and western edge of the Saskatchewan Commerce, 1960)) Plains and are underlain by gently westward-dipping Mesozoic strata. CONCLUSION that fo rm the bulk of t he Su­ The region is characterized by the perior Province. The cycle was re­ Porcupine Hills, Duck Mountain, The present physiography of Mani­ peated 1.7- 1.8 billion years ago, Riding Mountain, and Pembina toba h as been shaped by 3.5 billion fo rming the rocks of the Trans­ Mountain, whose western margin s years of geological history. Geologi­ Hudson Orogen in northwestern form the Manitoba E scarpment. Be­ cal activity continued fro m the Manitoba. There followed a long pe­ tween the "mountains" are broad early Precambrian and riod of general quiescence during valleys, fo rmed by the work of mountain-building events for a bil­ which the Precambrian Shield was preglacial rivers much larger than lion years to grind the Precambrian eroded down to a relatively fl a t the present misfi t streams. The sur­ Shield flat, so that the shallow seas plain that extends far to the west, face of these mountains, which at of the Paleozoic and Mesozoic could deep beneath the Rockies. t.heir highest rise 500 m above the lay down the limestones of the Throughout the Paleozoic and Manitoba Lowlands, is a relatively Manitoba Lowlands and the shales Mesozoic eras, continental drift flat plateau. Bedrock is exposed along of the Southwest Uplands. More re­ placed Manitoba near the equ ator. the escarpment face, but on the pla­ cently, glacial periods left a mant,]e At this time the Williston Basin teaus it is covered by great thick­ of deposits over much of the prov­ slowly subsided and was fill ed with nesses of glacial deposits, reaching ince and depressed the land to allow carbonate rocks, and newly evolv­ 250 m on Duck Mountain.21 the rivers to run across the Shield ing life forms fill ed the seas. DUTing In the south, Tur tle Mountain to Hudson Bay. the late Mississippian period the (7 57 m above sea level) is an ero­ Each event has left its finger­ sea receded, the waters became sional remnant, a topogr aphic fea­ print on the land. The P recambrian brackish and dissolved salts killed ture that remained after erosion produced early volcanism, left as off the animal life, and evaporites had reduced the surrounding area. greenstone belts that have provided and the last of the Paleozoic It is capped by rocks of Paleocene areas of mineral wealth. Then the dolomites were deposited. Then the age that are covered by thick (up to major Kenoran Orogeny about 2. 7 land emerged again from the wa­ 150 m) glacial drift.22 billion years ago produced the ex­ ters to be partially eroded away. tensive regions of granite and Later in the Mesozo ic t he seas 22 THE GEOGRAPHY OF MANITOBA returned, bringing more sedim nts mammal , occupied the land, and tinctive assemblage of landforms. and n w life forms in the waters, the stage was set for the Ice Age, The period since the Ice Age is and land animals appeared in areas during which the details of Manito­ ut an instant in geological tim . at the west rn edge of lh ~ province. ba's landscape were produced. Gla­ Neverthel S5, some details have By the end of the Cretaceous and cial el'osi n and deposition have been added to the physiographic earl. Tertiary, the land was once produced a variety of l an d~ rms. map, such as alterations in river again emerging from the seas. The Also, damming of the pregiaci I OlU'ses, D rm tion of sand dunes continent of North America slowly drainage by the ice resulted in a and uplift of glacially depressed drifted northward to its present 10­ number of glacial lake. , which in areas. The last, at least, continue . 'ation. Land animals, many ofthem turn have left behind their own dis-

NOTES Gl'(]ulid Water Re ources ofthe and L. Clayton , eds., Glacial Lake 1. When Rows are expell ed (ex­ Brandon Map-Area, Mafl itoba, Agassiz, Special Paper 26 (St. John's, truded) under \ ater, the outer surface Memoi r 300 (: Geological NF: Geological ssociation of Canada , f lhe lava cools qui<:kly, forming a Survey of Canada, 1960). 1 83), HI7-209. thin crust. Li quid parenL lava breaks 6 R. W, Klassen, Pleistocene Geology and 14. J.A. Elson, ~Geo l o gy of glacial Lake through the au t to form a series of of the R iding Moun· Agass i z,~ in W,J. Ma er- Oakes, ed., pillowli ke masses. Continua hon ofllie lain and Duck Muunlain Areas, Li{e, Land rind Water (Wi nnipeg: process produces a series of intercon­ Manitoba-Sashatchewan , Memoir 3913 niversity of Manitoba Press, ] 967), nected pIll ows. he signHicance of (Ottawa: Geological S urvey of Canada, 37- 95. pill ow If! at! is that they indicate 1979). 15. Klassen, Pleistocene Geology. underwater ormation. 7. Ison, "Sum inl geology." 16. Nielsen et aL, Surficial Geological 2. B.B. Banna t ne and J .T. Tell et·, 8. Klassen, Pleistocene Geology. Map of Manito ba. "~ o l ogy IJfManitoba before the Ice 9. J . WelRted and H . oung, "Geology 17. Ibid. Age," in NCtt urat Heritagp ofMani· and orib,;n of t he Bnmdon Hills, 18. RA McGinn, "A general de cription tuba: Legor'Y () f the Ice Age, ed . J.T. sou thwest Manitoba," Canadian of the eastern slopes ofR iding Teller (Winnipeg: Manitoba Museum J ournal ofEarth Sciences Mountain" (unpubli shed man cript, ofMan a nd Nalur', ] 984), 7- 21. 17(1980) 94 - 51. Brandon Uni versity, 1983). 3 E. Nielsen et aI., Surficio.l Gf'ologic.:ol 10. These are mapped a nd named in 19. W.J . Brown, "Geomorphology Field Map o{Maniloba, Map 1·1 (Winni­ I ielsen et aI., S urficial Geological Trip to Southw t Manitoba; ' in peg: Province of Manitoba, Depart­ Map of Manitoba. Department oj'Geography, University ment of Energy and Mines, 1981). 11 . Ibid. orManitoba Field Guide for the 4 When the ice sheets were no lo nger 12. l'.G. F isher and D. G. Smith, "North­ Canadian Association ofGeo oTaphers being replenished by sn wfall , the j 'C w st outlet of glacial Lake Agassiz: Annual Mee tinf{, ,Ju ne 1970 (Winni­ disappeared by stagnation and the Clearwater- Lake Athabaska peg: University of Manitoba, Depart­ dow wast.ing. Sedimen ts co nta ined I!p illway valleys," Abstract in Pro­ment of Geography, 1970), 43- 71. within the ice were deposited on the gramme with Abstracts, Third 20. M.H. War d, "Veget t ive Colonization land belnw, re ' ulting in an in:egu lar lnle rnatiulwl Geomorphology Co nfer­and Succes ion and th Impacts of lopography of hills nd depressions ence (Hamilton. ON: McMllilter 't'rampling in the Carberry Sand Hills, referred to as hum.mocky ground University, 1993), 139. Manitoba" (M.Sc. th sis, University of moraint: 01' hummQl'ky stagnation 13. A.E. Kehow a nd L. Clay ton, "Late ]\I[ nitoba , 1980 ). moraine. Wisconsinan fl oods and development 21. Nielsen et aI. , S urfici al Geological 5. J.A. Elson, "Surficial geology, Brandon of the Souris-Pembina spillway Map ufMan itoba. west ofprincip I meridian. Manitoba, ystem in Sru;katchewan, North 22. Ibid. Map ] 067A," in E .C. Haist 'ad, Dakota and Man itoba," in .J.T. Tell er Geology and Landforms ofManitoba 23

Case Study 2.1 local water table. In fact, the longest in Manitoba cave yet found in Manitoba, Laby­ Geraldine Sweet rinth Cave near , which measures over 180 m, is of this type. '" "Karst" is a term used to describe Often the tubes intersect, creating landscapes developed both on the small chambers at the intersections. surface and underground in regions The land surface in the Lake St. of soluble rock. Typical features Martin area resembles the classic Include pavements, depressions, cockpit karst of tropical regions, with caves, and springs. In Manitoba, many well-developed sinks coalesc­ throughout the southern Interlake ing, creating a densely pitted surface. region (the area between Lake The reason for the density of sinks ­ Winnipeg and Lakes Manitoba and an indicator of advanced develop­ Winnipegosis) and along the Hudson ment - is the extremely soluble Bay coast are extensive areas of nature of the rock. limestone, dolomitized limestone, (2) There is some surface expres­ and dolostone, all of which are sion of karst in the southern part of soluble to some degree in acid-rich, the Interlake, where the now-famous rr terrestrial water. These rocks occur at snake dens at Narcisse are examples --- ~ ~ ".'-: the surface or are covered by a of collapse sinks. Water below the S'If'lQO r. '~r", RI\#r variable layer of glacial debris. surface has dissolved the rock, Anhydrite (gypsum),l one of the creating cavities whose roofs have Figure 2 1.1 [,ocation of Karst Areas in most soluble of all rocks, is exposed subsequently collapsed. There are Mo.1!Itoba around Gypsumville. Although there much larger depressions of this are probably karst features wherever nature in places like Broad Valley, and Interlake (Figure 2.1. 2) . Here the these rocks occur (Figure 2.1.1), they farmers throughout the area tell tales bedrock is exposed over hundreds of are masked in the south and In the of pits and trenches they have filled square kilometres, with only a thin till far north by the glacial overburden. with rocks. cover in the lower areas. The result is There is evidence of large sinks in the At Inwood, Stony Mountain, and a region of well-developed karst bedrock below the city of Winnipeg, Garson, the limestone has been pavements, so named because the and large infilled cavities have been excavated for building material, surface resembles paving stones. In encountered in cores from the exposing extensive enlarged joint places, blocks have subsided or have Devonian rocks west of Lake Mani­ systems in the walls of the quarries, been dissolved to produce shallow toba. but the main area of cave develop­ bedrock sinks. In others, deep Surficial karst features are clearly ment is near Dallas, where a number trenches, or Lanjones, are the result defined, and cave passages reach the of explorable caves have been of joint enlargement by both chemi­ surface and can be explored in three discovered . Some are simply long cal and physical processes. regions in the province. trenches, widened by running water An escarpment marking the (1) Near Lake St. Martin (Figure just below ground level, probably boundary between the Silurian and 2.1.1), exposures of gypsum result in during the immediate postglacial Ordovician outcrops has a series of a well-developed landscape of period, when running water was springs along the base indicating the sinkholes, trenches,l and shallow more abundant. Some are easily underground drains of many of the caves. Because gypsum dissolves accessible through breaks in the roof. lakes on top of the escarpment. easily in water, this kind of karst is Others are more difficult to find; There are numerous collapse features usually quickly formed and relatively entrances are typically a small hole, similar to those at Narcisse, and short-lived. The present landscape is followed by a short drop into the many small, bell-shaped cavities. thought to be postglacial, the rock cave proper. St. George's Bat Cave is Caves were first discovered in the being so fragile that the ice would of this type: it opens out into a northern Interlake by hunters and probably have destroyed any surface sizable cavity about 5 m high and 165 trappers, but in the last 10 years a features. However, in some of the m long. It even has a side passage plan of exploration by Manitoba caves there is evidence of intense and some stalactites, formed by cavers has yielded many new cavities, folding of the bedrock that may have secondary .5 Altogether and more are being found each year. been glacially induced. eight smaJl caves have been found in Most are found within the top 20 m Because the rock is so malleable, this area, and exploration by the of the bedrock and range consider­ the caves vary considerably in form, Speleological Society of Manitoba is ably in shape and size, although they but the most common are long, continuing. are all small by world standards. narrow phreatiC tubes,3 which (3) The most extensive area of There seems to be a pattern to the formed below the piezometric both surface and underground development of the caves. In most surface (water table)4but which are features is between Grand Rapids cases the main excavation has oc­ now dry because of a lowering of the and William Lake, in the northern curred in the relatively soft and 24 THE GEOGRAPHY OF MAN ITOBA vuggy dolostone of the Atikameg uniV part of the Silurian, usually found 1- 3 m below the surface and overlain by thinly layered, fine­ grained rock. The Atikameg dolostone is easily dissolved and cavities have formed. later the roof collapsed, and in many cases the cave was enlarged along one or several fractures. In Dale's Cave, passages are phreatic, having formed below the piezometric surface. Most of the ..... DALE 'S CAV E ...... caves are still actively forming, as . " ••• I I there is often much water available '. , during spring melt when it is particu­ // -·::· t, ! ... larly aggressive, and therefore /~/ ,.. .~ / . / / ',,, / solution is rapid. In early spring /., ' . {{ l" , ... ' Moosearm Pit (Figure 2.1.3) has over / / " ~ , I ... I I /~/ II,;~ /1 I I • • a metre of meltwater sitting in it, ' / " / I J I • • ••• until ice in the floor melts and the I I . • I I I I I /A. .... *. I I I I I I MO OSEARM water disappears rapidly, suggesting •• ' , ','.,'• •• PIT well-developed drains in the bedrock .. . "', I I I.. below. Few of the caves have stalac­ II tites, probably because cave forma­ tion is stJII active, but there is some secondary precipitation in the form of the aptly named cave popcorn and dogtooth spar. Almost all the caves show evidence LAKE of physical - frost action - and the bedrock is generally shattered to a depth of at least 30 m. This is the result of postglacial pressure release and may account for ..I-L Escarpment the lack of an integrated cave system, ... Cave as water can move easily almost .. Small Sink anywhere in the rock. In the 1960s Spring decided to build a * Pavement dam on the at 0 10 , j Grand Rapids (Chapter 18). More km than a third of the cost was devoted to grouting the rock in the forebay, Figure 2.1.2 Karst Features of the Grand Rapids- William Lake Area to prevent water from escaping underground. Photographs taken at really caves, despite the names given than the air; in summer, colder. In the time show long, wide trenches in them by the Department of Natural many caves the roof is higher than the bedrock. Resources, but the collapse has the entrance, so "warm" air Is At , on the east side of occurred as a result of solutional trapped. The bats take advantage of , there are a whole widening of the natural joints of the this and hibernate rather than series of "sea" caves. Also, along the rock. migrate south. Some species of moth shore of Lake Winnipeg, lake water Although the caves in Manitoba do the same. Larger mammals, such has eroded the carbonate cliffs to are quite small, they are geologically, as porcupines and bears, sometimes create deep undercuts, cavities, hydrologically, and biologically use the caves as dens. arches, and stacks, a type of develop­ interesting. So far no evidence of Over a hundred individual caves ment found to a greater or lesser human occupation has been found, have been found in the province. extent on the shores of a number of other than the odd beer bottle or tin Perhaps in the future something lakes. In addition there are several can, but many of them are occupied larger will be found, as the environ­ locations in Provincial by colonies of Little Brown Bats ment is certainly conducive to karst Park and on Clearwater Lake, north­ (Myotis lucifus) . Caves have an ambi­ development. In the meantime, east of The Pas, where large sections ent temperature close to the annual Manitoba's caves provide a second, of cliff have collapsed, forming mean of the area, between -2°C and almost unknown landscape, under­ cavelike passages. The latter are not +1 °C, so in winter they are warmer ground. Geology and Landforms ofManitoba 25

4. A glossa ry of tec hnica l terms in included at the end of this case study. 5. "S peleothem" is the coll ective name for all forms of secondary precipitation in j;1>~ ~-.,"~- caves. Speleothems are formed when calCium sulphate-ri ch waters enter j _~ ,§f~ r·· open ca ve s and the pressu re release ,. causes deposition that cl ings to the ~ie _.; cave wall in much the sa me way as the "fur" in a . 6. Diffe rent m odes of form ation produce diffe rent fabri cs or textures in the rock . M uch of the ca rbonate found in Manitoba was formed in warm, shallow Estimated sp ring seas, where sediment w as trapped in meltwater level alga l mats . The resulti ng rock is crumbly an d full of spaces, or vu gs. Observed spring meltwater level ~ tFItrl~ GLOSSARY Zanjone - An enlarged fra cture, generally Figure 2.1 .3 Cross-profile of Mooseann Pit. in the Grand Rapids-William Lake Area asso ci ated with solution of carbonate (Source: From a survey by P Voitovici, C. S weet, et al.) rocks in the tropics . Cockpit kars t -An area of cl osely linked NOTES 3. The terms " phreatic" and "vad ose" depressions with remnant hills between 1. Gypsum is the hydrous form refer to the location of caviti es in them. (CaS O •. 2HP ) of anhydrite, a mineral re lation to the piezometric surface Piezometri c surface - The in terface so metimes found in large en ough (wate r table), and hence their method betw ee n rock containing freely moving masses to form a rock. It will dissolve in of formation. Vadose cavities are water and the saturated stratum (al so any liquid. formed when freely flowing w ate r ca ll ed the water ta bl e). 2. Some of these may simply be enlarge­ comes in contact with soluble rock; the Ca ve popcorn - Small g rowths of calcium ment of joints. In tropical environments emphasis is on downcutting, and the carbonate on ca ve wa lls an d ceilings; a th e term "l'anjone" is common, and upper parl of the cavity is frequently form of stal actite. refers to major enlargement by solution above the water. Phreati c ca vities form Dogtooth spa r - Seconda ry deposition of and subsequent collapse . Some of the below the w ater table; the entire pure or nearly pure ca lcium, sh aped like tren ches in the northern Interlake surfa ce will therefore undergo so lution teeth . exhibit similar characteristics. at the same time, creatin g round tubes that follow the dip of the rock .

Case Study 2.2 Description The Brandon Hill s John Welsted and Harvey R. Young The hills run for approximately 12 km A in a generally east-west direction, ~ In an area better known for its and are about 5 km across from north Om flatness than for hills, the Brandon to south. In places they rise 90 m Hills come as a surprise to the out­ above the surrounding landscape and sider. located approximately 20 km reach altitudes of over 480 m above south of Brandon, they rise promi­ sea level (Figure 2.2.2). Despite their -',...... J nently above the surrounding land­ limited area, they show considerable scape (Figure 2.2.1). They must "have variation in topography, leading us to been a welcome sight for a party of divide them into four physiographic settlers led by the Reverend George regions: (1) the main body of the Roddick from Pictou County, Nova hills, an area of irregular topography Scotia, who in May 1879 crossed the with some definite ridges; (2) the Assiniboine at Grand Valley three eastern ridge, a large, sinuous, miles downstream from the present­ generally north-south-trending ridge; day Brandon and saw an island of (3) the eastern complex, an area of Figure 2.2.1 Loca tio n of the Brandon Hills woodland set amidst a sea of waving mainly north-south-trending ridges grasses." l Although the surrounding and troughs east of, and adjacent to, land was soon prepared for agricul­ the eastern ridge; and (4) the south­ ture, the hills offered little agricul­ ern ridge, a northwest-southeast­ tural potential and have remained an trending ridge. 2 island of natural vegetation sur­ The main body of the hills consists rounded by cultivated land. of a series of subparallel ridges that 26 THE GEOGRAPHY OF MANITOBA trend northwest-southeast in the west, more nearly west-east in the centre, and swing around to become almost north-south In the east. These t ~r.lllJ~ :" are mainly wooded (poplar, scrub , t_ " ~,.. '\ "_ oak, and Manitoba maple), but some LJ of the more prominent ones have " / ~s, only a sparse grass cover. A profile drawn across them along the hydro I,' It· " road reveals that the topography is I,. ~I '(), hummocky, with the south side of the 'c' hills being steeper than the north I~ side (Figure 2.2.3). Glacial till is ../' .y ~ . '" . ~-::.. .•. =. exposed in the road cuts along this ----,~ - minor highway. The eastern ridge is quite differ­ • II ent. It has been described as looking Figure 2.2.2 Topography ofthe Brandon Hills "as if an enormous dump truck has moved along depositing piles of dirt every few hundred metres."l Many do not recognize it as a ridge because ..0-1------­ ----too-=-,oa..-...... ,I

Geo logy and Landforms ofManitoba 27 sorted deposits are clearly of glaciofluvial origin; that is, they were deposited by water in association with ice. These are overlain by till, a true glacial deposit. Initially we believed that the ridges of the main body of the hills resulted from the irregular deposition of till as the ice front receded, but we now believe that they are of glaciofluvial origin and that the overlying till was depos­ ited on preexisting ridges. Both the eastern ridge and the southern ridge have many of the characteristics of an esker - a landform thought to originate by deposition in tunnels in a glacier or an ice sheet, the deposits being left behind in a ridgelike form when the ice melts. Because the sediments were deposited by running water, they are layered and sorted. The till patches and the scattered erratics on Figure 2.2.4 T he S teep East-facing ( Photawaph: ·fohn Wel.s t ~ J ) the ridges would have been depos­ ited by the overlying ice as it melted. Both the eastern ridge and the southern ridge can be categorized as eskers, although the eastern ridge in particular is much higher than any other esker mapped in southern Manitoba.s The eastern complex is sufficiently similar in both composi­ tion and topography to the eastern and southern ridges to suggest that it has a similar origin. The description of the Brandon Hills as an end moraine can be regarded as the "traditional" expla­ nation. However, an alternative is provided by Aber, who claims that the hills are glaciotectonic in origin. He explains the ridges of the main body as being due to ice thrusting, with great slabs of previously depos­ ited glacial sediment, or bedrock, being pushed forward by the advanc­ ing ice. Despite this explanation for the main body, he still regards the eastern and southern ridges as eskers ,6 Whatever the origin of the Brandon Hills, they are a largely unspoiled landform that has main­ tained its natural vegetation and that offers a variety of opportunities for the outdoors person,

Fig ure 2.2.5 The Eastern Part af the Brandan Hills. The grass-I'o(.'er('ri eastern ridge !light· tunpd) crosses the area frum narth (a t the tap af the photagraph) to. sauth ; thi> f!<1s tern complex is located east of the ridge and highway ,744 i .~ ea"f aOhat. (j)hota{!ra ph: NAPL Al64 08·.9) 28 THE GEOGRAPHY OF MANITOBA

NOTES 3. ) Wel sted and H. You ng, "The Bl ue Hi lls of the Bran don Hi lls are commonly in 1. J. Wel sted and H. You ng, "The Blue Hills of Bra ndon," 35 . the order of 10m in height. of Brandon," Manitoba Nature (Autumn 4. The relevant map is 62G/l 2 Wawan esa . 6. J.S . Aber, "Spectrum of Constructional 1972):3 2. A survey point located near the ce ntre Lan dforms," in Genetic Classification of 2. J. W Isted and H. Young, "Geology and of the ridge has the exact height Glaciogenic Deposits, ed . R.P. Goldthwait ori gin of the Bra ndon Hills, Southw est 1566.3 fee t (477.4 m). and c.L. Ma ts ch (Ro tterdam : A.A. Manitoba, " Canadia n journal of Earth 5. Eske rs in the Baldur, Notre Dame de Balkema, 1989), 281-92; Figure 4. Sciences 17(1980):942- 51. Lourdes, and Bruxelles area to the east

Case Study 2.3 (1) WILLOWBENO PHASE (2 ) flEE ISLANO PHASE Lu!.:/! L WF. Ronnie

The "Forks" at the confluence of the Assiniboine and Red rivers has -) become one of Winnipeg's best­ ~ known features, the focus of major redevelopment and a source of international acclaim (Case Study (3) LONG LAKE · HIGH BLUFF (4) BLI ND PHA SE 10.1 on page 150). less well known is u.k,· the fact that The Forks has not always PHASE 4.5 20 Years Ago .\/III1I1O/> ? Yea rs Ag o \((//11/11/'" been at its present location; indeed, It., there has not always even been a .., , .... -'------­ Forks. About 3,000 years ago, The ~ )t. , ,-- ,, - ­ - , --.. Forks was at St. Norbert, 14 km to the ~ "''''... ,II : .. ,," --- ...... -- - ... south, where the La Salle River joins - ., the Red, and for several thousand l' years before that the Assiniboine did not join the Red at all but flowed north from into (5) LA SALLE PHASE (6) Mill PHASE lake Manitoba. These and other Luke 2,980 Years Ago 1.300 Yea rs Ago routes of the Assinibolne River are .If 1111/, be ' HlII,ilflbCl shown schematically In Figure 2.3.1. ... ,,"...- ...... > ----­ The cause of these dramatic changes ~ "" '\ , ... ,," - - ~ \ I I " lies with the Portage la Prairie alluvial I ,. ... " fan, an unusual feature that, al­ - ' ~ though barely noticeable on the --~ ground, has produced an evolution of the Assiniboine River with few, if any, counterparts elsewhere in the world. (7) CURTIS RIDGE PHASE • (8) ASSINIBOIN EP HASE Most alluvial fans are small, steep 70 0 Years Ago Lukt' Present features composed of coarse materi­ Me//fIIIIP" als deposited by multichannel streams with "flashy" (frequently \ I ...... ephemeral) flow regimes in dry " \ I , climates. The fan constructed by the ," , t' .. ' _ ..... I \

Assiniboine has none of these charac­ --~ teristics. The river Itself is perennial, carries a modest sediment load, and has a strongly meandering single­ Figure 2.3.1 E volution of the Lower As::;iniboine River channel pattern. The fan it has produced has a very low gradient, is composed of relatively fine materials, location at the point where the associated with floodplain formation and is an order of magnitude larger Assiniboine emerges from its confin­ by a laterally mobile meandering than most other contemporary fans. ing valley onto the l ake Agassiz Plain stream. Deposition In and near the Only in two crucial respects does it (Chapter 2). river channel repeatedly elevated the resemble other fans: the radial The Portage la Prairie fan was river on an alluvial ridge. As it gr w configuration of channels, and its produced by processes normally higher above the surrounding Geology and L a ndform s of Manitoba 29

Portage la Prairie, this large artificial channel enables water to be diverted c...... C' Locati on of Fan Profile from the Assiniboine to lake Mani­ Boundary of Allu vial Fan toba to reduce flow through Winni­ Escarpment peg during major floods (and inci­ dentally to reduce flooding on the alluvial fan) . This diversion was possible only because of the elevation of the river provided by the fan near Portage la Prairie. Its value was demonstrated during truly exceptional floods in 1974 and 1976, when much of the alluvial fan and lower terrain would otherwise have been inundated. N More importantly perhaps, given the A elevated state of the Assiniboine, ~---.!O these floods might have triggered km avulsive channel abandonment, which would have required expensive remedial works. Thus, human modifi· Figure 2.3.2 Paleochannels of the Lower Assiniboille R iver, S howing the Locotion ofProfiles cation of the flood regime has in Figure 2.3.3 probably ended the period of active fan formation.

terrain, it became increasingly present location at The Forks, but NOTE S unstable and was eventually aban­ differed from its modern course on 1. For more details, see W. F. Rannie, L.H. doned in favour of a new lower the fan. The upper fan section of the Thorleifso n, and J.T. Tell er, " Holocene Evolution of the Assiniboine River course, a process called avulsion. Each river was altered again by 700 B.P. in Paleochannels an d Portage la Prairie of these episodes left an abandoned the Curtis Ridge Phase. Thus, the Alluvial Fans," Canadian Journ al of Ea rth ridge-channel system, or modern route of the Assiniboine Sciences 26( 1989): 1834-41; and W. F. paleochannel (Figures 2.3.2 and from Portage la Prairie to Winnipeg is Rannie, "The Portage la Prairie 2.3.3), with features such as scroll somewhat less than 700 years old.' ' Flo odp lain Fan'," In Alluvial Fans : A Field bars that show clearly on aerial Interestingly, maps of the soils in Approach, ed . A. H. Rachocki an d M. photographs (Figure 2.3.4). the Portage la Prairie area reflect this Church (Chichester, Englan d: John Wiley and So ns, 1990), 179-93. The Initial courses of the river evolution. Soils adjacent to the were northward to Lake Manitoba. northward channels, being older, The oldest paleochannel, display mature chernozemic A Willowbend, was active before 7000 horizons (Chapter 4), whereas those B.P., or shortly after the recession of south of the present Assinlboine have lake Agassiz water from the region. immature, thin, organic layers, as Drainage into lake Manitoba shifted would be expected in much younger to the Flee Island channel and finally, sediments. The shift in outlet from by 4500 B.P., to Blind channel, which lake Manitoba to the Red River about remained active at least until 3400 3,000 years ago coincided with a B.P. As the region between present­ sharp reduction in sedimentation in day Portage la Prairie and Lake lake Manitoba and increased the Manitoba became "filled" with sediment and water inflow to the sediments and paleochannels, further Red. Although the sedimentation avulsion exploited lower terrain and history of lake Winnipeg Is not steeper gradients to the east, divert­ known, an Increase in the last 3,000 Ing the ancestral Assiniboine away years would be expected. from lake Manitoba and towards the Until recently, alluvial ridge Red River. formation continued to elevate the The firs t eastward route was modern Assiniboine channel on the established by about 3000 B.P. along fan, producing a potential for future the channel now occupied by the La catastrophic channel abandonment Salle River, joining the Red In during large flood events. This present-day St. Norbert. By about potential was greatly reduced in 1, 300 years ago (in the Mill Phase), 1970, however, by the opening of the the lower Assiniboine had shifted Portage Diversion (Case Study 18.2 northward to join the Red at its on page 283). located just west of 30 THE GEOGRAPHY OF MANITOBA

A I ASSUUIDIIl E

~I'-I~ .. .. lLE I" " ~A '

8 A&! IN UI OI NF. ~ ~ LAA'~ - U l '-./ u~,

"'

LA UlLE C'

Figure 2 ..1.3 Cross-profil es of the A.~ s ilL ib oi ne Fall South of'the Assiniboine RivP.r, Showing Major Alllw ial Ridges

Figure 2.3.4 Paleochannels South ofthe Assiniboine River. The Trans-Canada Highway crosse' the area in the north at the top of' th e photograph. (Photograph: Ma nitoba Air Photo Library IMAPLJ MB 89021-J76)