,glaciers and ,glaciation in ,glacier ,national ,park ,price #ce ,cents ,illustration3 ,,published ,,by ,,the ,,glacier ,,natural ,,history ,,association ,,in ,,cooperation ,,with ,,the ,,national ,,park ,,service ,illustration3 ,,national ,,park ,,service ,cover ,surveying ,sperry ,glacier--,arthur ,johnson of ,u4 ,s4 ,g4 ,s4 ,n4 ,p4 ,s4 ,photo by ,j4 ,w4 ,corson ,,revised #aiff ,,reprint #aiga ,,thomas ,,printing #e,m#ga ,,glaciers ,,and ,,glaciation ,,in ,,glacier ,,national ,,park ,by ,james ,l4 ,dyson#a ,head1 ,department of ,geology and ,geography ,lafayette ,college ,the glaciers of ,glacier ,national ,park are only a few of many thousands which occur in mountain ranges scattered throughout the world4 ,glaciers occur in all latitudes and on every continent except ,australia4 ,they are present along the ,equator on high volcanic peaks of ,africa and in the rugged ,andes of ,south ,america4 ,even in ,new ,guinea1 which many think of as a steaming1 tropical jungle island1 a few small glaciers occur on the highest mountains4 ,almost everyone who has made a trip to a high mountain range has heard the term1 8snowline10 and many persons have used the word without knowing its real meaning4 ,the snowline is the level above which more snow falls in winter than can be melted or evaporated during the summer4 ,on mountains which rise above the snowline glaciers usually occur4 ,the snowline is an elusive feature and can be seen only in late summer4 ,for example1 during the latter part of ,june snow extends from the summits of most ,glacier ,national ,park mountains down their slopes to timberline1 and some snowbanks extend even lower4 ,at that time the snowline appears to be down near timberline4 ,but as the summer progresses and higher temperatures melt the lower-lying snowbanks this apparent snowline retreats higher and higher up the slopes1 until late ,august or early ,september1 when it reaches a point above which it will not retreat4 ,this lower limit of snow is the permanent or regional snowline4 ,it is usually referred to simply as the snowline4 ,in ,glacier ,national ,park the regional snowline actually lies above the summits of most peaks1 at a height of more than #aj1jjj feet4 ,the only parts of the ,united ,states south of ,canada which project above the snowline are the highest summits in the ,cascade ,range in ,california1 ,oregon1 and ,washington1 and in the ,olympic ,mountains in the latter state4 ,there are many mountains in ,alaska that lie above the snowline4 ,this is especially true in the coastal ranges where the snowline is around #d1ejj feet above sea level4 ,the ,olympic area is unique1 for here the regional snowline descends to about #f1jjj feet lower than anywhere within the boundaries of the ,continental ,united ,states south of ,alaska4 ,extraordinarily heavy annual snowfall and the high percentage of cloudy weather1 which retards the melting of snow1 combine to depress the snowline to such a low level4 ,glaciers of ,glacier ,national ,park ,within the boundaries of ,glacier ,national ,park there are #ej to #fj glaciers1 of which only two have surface areas of nearly one-half square mile1 and not more than seven others exceed one-fourth square mile in area4 ,all these bodies of ice lie at the heads of valleys with high steep headwalls on the east and north sides of high ridges at elevations between #f1jjj and #i1jjj feet1 in all cases well below the snowline4 ,consequently1 these glaciers owe their origin and existence almost entirely to wind-drifted snow4 ,ice within these glaciers moves slowly4 ,the average rate in the smallest ones may be as low as #f to #h feet a year1 and in the largest probably #be to #cj feet a year4 ,there is no period of the year when a glacier is motionless1 although movement is somewhat slower in winter than in summer4 ,despite the slowness of its motion the ice1 over a period of years1 transports large quantities of rock material ultimately to the glacier's end where it is piled up in the form of a moraine4 ,illustration3 ,,front ,,of ,,sperry ,,glacier ,the largest glacier in the ,park is ,grinnell4 ,in #aifj it had a surface area of #cae acres4 ,sperry is the second largest glacier in the ,park4 ,its surface in #aifj was #bhg acres4 ,both ,grinnell and ,sperry have probable maximum thicknesses of #djj to #ejj feet4 ,illustration3 ,,jackson ,,glacier ,,is ,,visible ,,from ,,going-,,to-,,the-,,sun ,,road 7,,beatty ,,photo7 ,other important ,park glaciers1 although much smaller than the first two mentioned1 are ,harrison1 ,chaney1 ,sexton1 ,jackson1 ,blackfoot1 ,siyeh1 and ,ahern4 ,several others approach some of these in size1 but because of isolated locations they are seldom seen4 ,as a matter of fact1 there are persons who visit ,glacier ,national ,park without seeing a single glacier1 while others1 although they actually see glaciers1 leave the park without realizing they have seen them4 ,this is because the highways afford only distant views of the glaciers1 which from a distance appear much like mere accumulations of snow4 ,a notable example is ,grinnell as seen from the highway along the shore of ,sherburne ,lake and from the vicinity of the ,many ,glacier ,entrance ,station4 ,the glacier1 despite its length of almost a mile1 appears merely as a conspicuous white patch high up on the ,garden ,wall at the head of the valley4 ,several of the glaciers1 however1 are accessible by trail and are annually visited by many hundreds of people1 either on foot or by horse4 ,most accessible of all ,park glaciers is ,grinnell4 ,it can be reached by a six-mile trip over an excellent trail from ,many ,glacier ,hotel or ,swiftcurrent ,camp4 ,sperry1 likewise1 can be reached by trail1 although the distance is several miles greater than in the case of ,grinnell4 ,the trip1 however1 can be broken and possibly made more interesting by an overnight stop at ,sperry ,chalet1 which is located about three miles from the glacier4 ,siyeh is the only other regularly visited ,park glacier4 ,it lies about half a mile beyond the end of the ,cracker ,lake trail1 and can be reached from that point by an easy walk through grassy meadows and a short climb over a moraine4 ,siyeh1 however1 is less spectacular than either ,grinnell or ,sperry1 being much smaller and lacking crevasses1 so common on the other two4 ,few people make the spectacular trail trip over ,siyeh ,pass but those who do may visit ,sexton ,glacier by making a short detour of less than half a mile where the trail crosses the bench on which the glacier lies4 ,sexton is a small glacier1 but late in the summer after its snow cover has melted off it exhibits many of the features seen on much larger bodies of ice4 ,interesting surface features which can be seen at times on any of these glaciers include crevasses1 moulins 7glacier wells71 debris cones1 and glacier tables4 ,crevasses are cracks which occur in the ice of all glaciers4 ,they are especially numerous on ,sperry and ,grinnell4 ,moulins1 or glacier wells1 are deep vertical holes which have been formed by a stream of water which originally plunged into a narrow crevasse4 ,continual flow of the stream enlarges that part of the crevasse1 creating a well4 ,several such features on ,sperry ,glacier have penetrated to depths of more than #bjj feet1 and are #bj or more feet wide at the top4 ,no one can walk over the surface of ,grinnell ,glacier without noticing a number of conical mounds of fine rock debris4 ,actually these are cones of ice covered with a veneer1 seldom more than two inches thick1 of rock debris1 so their name1 debris cone is somewhat misleading4 ,illustration3 ,,crevasse ,,in ,,sperry ,,glacier ,this rock material1 usually deposited by a stream1 protects the ice underneath from the sun's rays4 ,as the surface of the glacier1 except that insulated by the debris1 is lowered by melting1 the mounds form and grow gradually higher until the debris slides from them1 after which they are speedily reduced to the level of the rest of the surface4 ,they are seldom higher than #c or #d feet4 ,a glacier table is a mound of ice capped1 and therefore protected from melting1 by a large boulder4 ,its history is similar to that of the debris cone4 ,after a time the boulder slides off its perch1 and then the mound of ice melts away4 ,snow which fills crevasses and wells during the winter often melts out from below1 leaving thin snowbridges in the early part of the summer4 ,these constitute real hazards to travel on a glacier because the thinner ones are incapable of supporting a person's weight4 ,this is one very good reason why the inexperienced should never venture onto the surface of a glacier without a guide4 ,it is probable that the ,park glaciers are not remnants of the large glaciers present during the ,ice ,age which terminated approximately #aj1jjj years ago1 because it is known that several thousand years after that time the climate of the ,glacier ,national ,park region was somewhat drier and warmer than now4 ,under such conditions it is probable that most1 if not all1 of the present glaciers could not have existed4 ,shrinkage of ,park ,glaciers ,prior to the beginning of the present century all glaciers in the ,park1 and most of those in the rest of the world1 began to shrink in response to a slight change in climate1 probably involving both a temperature rise and a decrease in annual snowfall4 ,from about #aijj to #aide shrinkage of ,park glaciers was very rapid4 ,in other words these glaciers were not in equilibrium with the climate1 for less ice was added to them each winter than disappeared by melting and evaporation during the remainder of the year4 ,over a period of several years such shrinkage is apparent to the eye of an observer and is manifest by a lowering of the glacier's surface1 and more particularly by a 8retreat0 of the lower edge of the glacier4 ,this part of the ice is generally referred to as the ice front4 ,when sufficient snow is added to the upper part of the glacier to cause the ice at the front to move forward equal to the rate at which it melts away1 the glacier is in equilibrium with the climate4 ,when the yearly added snow decreases in amount the ice front seems to retreat or move back1 whereas the mass of the glacier is merely decreasing by melting on top and along the edges1 just as a cube of ice left in the kitchen sink decreases in size4 ,the ,national ,park ,service initiated observations on glacier variations in #aica4 ,at first the work consisted only of the determination of the year by year changes in the ice front of each of the several glaciers4 ,from #aicg to #aici1 inclusive1 the program was expanded to include the detailed mapping of ,grinnell1 ,sperry1 and ,jackson ,glaciers to serve as a basis for comparisons in future years4 ,aerial photographs were obtained of all the known ,park glaciers in #aiej and #aieb and again in #aifj4 ,maps have been compiled and published of the ,grinnell and ,sperry ,glaciers based on the #aiej and #aifj aerial photography4 ,the #aiej and #aifj maps of each glacier are shown on one sheet for convenience in comparison4 ,since #aide1 the glacier observations have been carried on in cooperation with the ,u4 ,s4 ,geological ,survey4 ,the work has included the periodic measurement of profiles to determine changes occurring in the surface elevation of ,grinnell and ,sperry ,glaciers and also the determination of the rate of annual movement4 ,some of the more important data yielded by surveys on ,grinnell and ,sperry1 the two largest glaciers in the ,park1 are summarized in the following tabulations3 ,,grinnell ,,glacier ,year ,area ,remarks 7,acres7 #aija #ebe ,from ,chief ,mountain topographic quadrangle map4 #aicg #chd ,from mapping by ,j4 ,l4 ,dyson and ,gibson of lower portion of glacier plus area of upper glacier 7#ef acres71 as shown on #aiej ,,usgs map4 #aidf #ccf ,as above4 #aiej #cbh ,from ,,usgs map compiled from aerial photography4 #aifj #cae ,as above4 ,the ,grinnell ,glacier originally consisted of an upper and lower portion connected by an ice tongue4 ,this tongue disappeared in #aibf and since then the two portions have been separate4 ,the area of the upper portion of the glacier was essentially the same in #aifj as in #aief--ef acres4 ,the upper section is known as ,salamander ,glacier because of its shape as viewed from a distance4 ,the terminal recession of the ,grinnell ,glacier is somewhat difficult to determine accurately as a part of the terminal portion ends in a lake1 the shore of which varies from year to year4 ,the recession for a half-mile section extending southeast from the lake is shown below3 ,period ,recession during ,total ,recession ,average annual period 7feet7 since #aicg 7feet7 recession 7feet7 #aicg-de #bgj #bgj #cd #aide-ej #ge #cde #ae #aiej-fj #he #dcj #h ,the values for area and recession shown above indicate that changes in the area of the glacier have not been as pronounced since the mid-#aidj's as they were prior to that time4 ,profile measurements starting in #aiej indicate a general trend of continued shrinkage although annual changes have been both positive and negative4 ,the #aife observations showed a surface lowering of #bj to #be feet1 since #aiej4 ,the movement of the ,grinnell ,glacier1 based on observations since #aidg1 has been about #ce to #dj feet per year4 ,the ,sperry ,glacier is located #i miles from the ,grinnell ,glacier1 on the opposite side of the ,continental ,divide and at an altitude approximately #a1jjj feet higher4 ,it has also shown a continual shrinkage in area and recession of the terminus as shown by the following tabulations3 ,,sperry ,,glacier ,year ,area ,remarks 7,acres7 #aija #haj ,from ,chief ,mountain topographic quadrangle map4 #aich #cij ,from mapping by ,j4 ,l4 ,dyson and ,gibson4 #aidf #ccj ,from mapping by ,j4 ,l4 ,dyson4 #aiej #cje ,from ,,usgs map compiled from aerial photography4 #aifj #bhg ,from ,,usgs map compiled from aerial photography4 ,recession1 in feet1 of central half-mile section of terminus ,period ,recession ,total recession ,average annual since #aich recession #aich-de #cea #cea #ej #aide-ej #agg #ebh #ce #aiej-fj #bdd #gib #bd ,profile measurements1 starting in #aidi1 indicate a continued lowering of the glacier surface below an altitude of about #g1ejj feet4 ,above this altitude it has remained much the same during the period of observations with annual changes1 both positive and negative1 with a possible slight net increase since #aidi4 ,the forward movement in the central portion of the ,sperry ,glacier1 based on observations since #aidi1 has averaged about #ae feet per year4 ,the rate of movement is presumed to be greater in the upper reaches of the glacier4 ,it is of interest to note from the data that the changes in ,sperry ,glacier are more pronounced than those in ,grinnell ,glacier although the straight-line distance between them is only #i miles4 ,one possible reason--,grinnell ,glacier is on the eastern slope of the ,continental ,divide whereas ,sperry ,glacier is on the western slope4 ,even more significant is the lowering of the glacier's surface1 from which volume shrinkage may be obtained4 ,in #aich ,sperry ,glacier had a thickness of #ajh feet at the site of the #aidf ice margin4 ,at this same place in #aiac the thickness was nearly #ejj feet1 and the average thickness of the glacier over the area from which it has since disappeared was at least #cjj feet4 ,the average thickness of ,grinnell ,glacier in #aicg at the site of the #aidf ice front was #gc feet4 ,the surface of the entire glacier was lowered #ef feet during that nine-year period4 ,this means that each year the glacier was reduced in volume by an amount of ice equivalent to a cube #dej feet high4 ,illustration3 ,,grinnell ,,glacier ,,as ,,it ,,looked ,,prior ,,to #aibf ,,when ,,the ,,lower ,,and ,,upper ,,segments ,,were ,,still ,,connected4 ,at the northern terminus of ,grinnell ,glacier1 which is bordered by a small marginal lake1 a large section of the ice front fell into the water on or about ,august #ad1 #aidf1 completely filling it with icebergs4 ,this event1 although witnessed by no one1 must have been comparable to many of the icefalls which occur at the fronts of the large glaciers along the southeast coast of ,alaska4 ,the volume of ,grinnell ,glacier was reduced by about one-third from ,september #aicg to ,september #aidf4 ,several other glaciers have exhibited a more phenomenal shrinkage than ,sperry or ,grinnell4 ,the topographic map of ,glacier ,national ,park1 prepared in #aijj-aijb1 shows several comparatively large glaciers such as ,agassiz1 ,blackfoot and ,harrison4 ,their shrinkage has been so pronounced that today ,agassiz has virtually disappeared and the other two are pitifully small remnants1 probably less than one-fifth the size they had been when originally mapped4 ,since #aide1 because of above-normal snowfall and subnormal temperatures1 glacier shrinkage has slowed down appreciably1 coming virtually to a standstill in #aiej2 and in #aiea1 for the first time since glacier changes have been recorded in the ,park1 ,grinnell ,glacier increased slightly in volume4 ,this was also reflected by a readvance of the front4 ,although no measurements were made in #aiea on other ,park glaciers some of them certainly made similar readvances4 ,thus the climatic conditions which caused glaciers to shrink for fifty or more years seem to have been replaced by conditions more favorable to the glaciers4 ,time alone will tell whether the new conditions are temporary or mark the beginning of a long cycle of wetter and cooler climate4 ,former ,extent of ,park ,glaciation ,during the ,pleistocene ,period or ,ice ,age when most of ,canada and a large portion of the ,united ,states were covered several times by an extensive ice sheet or continental glacier1 all the valleys of ,glacier ,national ,park were filled with valley glaciers4 ,these originated in the higher parts of the ,lewis and ,livingstone ,ranges4 ,on the east side of the ,lewis ,range they moved out onto the plains4 ,from the ,livingstone ,range and the west side of the ,lewis ,range they moved into the wide ,flathead ,valley4 ,during the maximum extent of these glaciers all of the area of the ,park except the summits of the highest peaks and ridges were covered with ice4 ,the great ,two ,medicine ,glacier1 with its source in the head of the ,two ,medicine and tributary valleys1 after reaching the plains spread out into a big lobe 7piedmont glacier7 eventually attaining a distance of about #dj miles from the eastern front of the mountains4 ,the stream of ice emerging onto the plains from ,st4 ,mary ,valley also extended many miles out from the mountain front4 ,several of these long valley glaciers extended far enough out onto the plains to meet the edge of the vast continental ice sheet moving westward from a center in the vicinity of ,hudson ,bay4 ,in the major ,park valleys these glaciers attained thicknesses of #c1jjj or more feet4 ,although man probably never viewed this magnificent spectacle1 the ,park at that time must have been similar in aspect to some of the present day ice filled ranges along the ,alaska-,yukon border4 ,no one knows exactly how many times glaciers moved down the ,park valleys during the million or more years of the ,pleistocene period1 but geologists have found evidence for at least eight distinct advances4 ,it is difficult to determine just when the first advance took place but it may have been very early in the period4 ,most of the advances1 however1 occurred during the past #gj1jjj years or so in what is known as the ,wisconsin stage of the ,ice ,age4 ,large glaciers flowed down the ,park valleys probably as late as #g1jjj years ago4 ,between each of the major times of ice advance1 the glaciers1 responding to warmer or drier climate1 shrank to small size and in some instances disappeared4 ,these warmer intervals varied in length from #b1jjj to tens of thousands of years4 ,evidence of the several distinct glacial advances is yielded by the moraines1 deposits of rock debris left by the ice4 ,on the east side of the ,park the lower courses of the major valleys and the adjoining ridges in the ,park and on the adjacent plains are covered with moraines4 ,the material in them ranges in size from clay to large boulders1 and was deposited by glaciers after being transported down the valleys4 ,the debris deposited by the latest ice advance is fresh in appearance and contains fragments of all ,park rocks4 ,moraines of the earlier stages1 because of much greater age1 are more weathered4 ,they contain many fragments of much weathered diorite1 from the layer of rock that appears as a conspicuous black band on many of the mountains1 and almost no fragments of limestone1 so common in the newest moraines4 ,the diorite is more resistant to weathering than the limestone which slowly dissolves in ground-water4 ,the only localities where the oldest moraine occurs are the crests of the ridges which run eastward from the mountains out onto the plains4 ,this material is especially abundant on ,st4 ,mary ,ridge4 ,on top of ,two ,medicine ,ridge along and just above the highway1 fragments of this material have been cemented together into a comparatively hard tillite4 ,lower down on the slopes the older moraine cannot be found as it is covered by that of the later glacial advances which were less extensive and did not override the ridge crests as did the earlier glaciers4 ,the older debris is also found on top of ,milk ,river and ,boulder ,ridges4 ,following the last maximum advance of the ,wisconsin glaciers they slowly shrank until about #f1jjj years ago when all glacial ice probably disappeared from the mountains4 ,after this there was a warm1 dry period during which it is probable that no glaciers were present4 ,then about #d1jjj years ago the present small glaciers were born4 ,during the period of their existence they have fluctuated in size1 probably attaining maximum dimensions around the middle of the last century4 ,since then they have been getting smaller4 ,illustration3 ,,panoramic ,,view ,,of ,,grinnell ,,glacier ,,as ,,it ,,appeared ,,in #aide4 ,,the ,,crevasses ,,in ,,glacier ,,may ,,be ,,over #ej ,,feet ,,deep 7,,beatty ,,photo7 ,illustration3 ,,panoramic ,,view ,,of ,,sperry ,,glacier ,,as ,,it ,,appeared ,,in #aidf4 ,,note ,,melt-,,water ,,lakes ,,terminating ,,against ,,moraines ,,at ,,extreme ,,left 7,,dyson ,,photo7 ,park ,features ,resulting ,from ,glaciation ,a glacier is an extremely powerful agent of erosion1 capable of profoundly altering the landscape over which it passes4 ,glaciers erode mainly by two processes1 plucking and abrasion4 ,the first is more active near the head of the glacier1 but may take place anywhere throughout its course2 abrasion or scouring is effective underneath most sections of the glacier1 particularly where the ice moves in a well-defined channel4 ,illustration3 ,,mt4 ,,oberlin ,,cirque ,,and ,,bird ,,woman ,,falls 7,,hileman ,,photo7 ,in plucking1 the glacier actually quarries out masses of rock1 incorporates them within itself1 and carries them along4 ,at the head of the glacier this is accomplished mainly by water which trickles into crevices and freezes around blocks of rock1 causing them to be pulled out by the glacier1 and also by the weight of the glacier1 squeezing ice into the cracks in the rock4 ,as the glacier moves forward these blocks of ice are dragged or carried along with it4 ,usually a large crevasse1 the bergschrund1 develops in the ice at the head of a glacier4 ,the bergschrund of most glaciers in the park consists of an opening1 usually #aj to #bj feet wide at the top and as much as #ej feet deep1 between the head of the glacier and the mountain wall4 ,on ,sperry ,glacier1 however1 it is more typical of that found on larger valley glaciers and consists of several conspicuous crevasses separating the firn area 7where the snow is compacted into ice7 on top of ,gunsight ,mountain from the glacier proper below 7see photo on the cover74 ,it is at this site that plucking is most dominant because water enters by day and freezes in the rock crevices at night4 ,this quarrying headward and downward finally results in the formation of a steep-sided basin called a cirque or glacial amphitheatre4 ,because the cirque is the first place that ice forms and the place from which it disappears last1 it is subjected to glacial erosion longer than any other part of the valley4 ,thus its floor is frequently plucked and scraped out to a comparatively great depth so that a body of water known as a cirque lake forms after the glacier disappears4 ,iceberg ,lake lies in one of the most magnificent cirques in the ,park4 ,the lowest point on the crest of the wall encircling three sides of the lake is more than #aejj feet above the water4 ,prior to #aidj this cirque contained a small glacier4 ,it has been shrinking rapidly for about two decades1 and in the last two or three years of its existence was hardly recognizable as a glacier4 ,its disappearance is made more remarkable by the knowledge that in #aibj the front of the glacier rose in a sheer wall of ice nearly #ajj feet above the surface of the lake4 ,all that remains of this glacier which once kept the lake filled with icebergs each summer is a large bank of snow at the base of the cirque wall at the head of the lake4 ,other good examples of cirques are those which hold ,hidden1 ,avalanche and ,cracker ,lakes4 ,the tremendous cliff on the south side of the latter rises #d1ajj feet from the lake to the summit of ,mount ,siyeh4 ,other notable cirque lakes are ,ellen ,wilson1 ,gunsight1 ,ptarmigan and ,upper ,two ,medicine4 ,illustration3 ,,st4 ,,mary ,,valley ,,from ,,logan ,,pass ,,showing ,,glacial ,,profile 7,,hileman ,,photo7 ,rock fragments of various sizes frozen into the bottom and sides of the ice form a huge file or rasp which abrades or wears away the bottom and sides of the valley down which the glacier flows4 ,the valley thus attains a characteristic ,u-shaped cross section1 with steep sides 7not necessarily vertical7 and a broad bottom4 ,a mountain valley cut entirely by a stream does not have such shape because the stream cuts only in the bottom of the valley1 whereas a glacier1 filling its valley to a great depth1 abrades along the sides as well as on the floor4 ,practically all valleys of the ,park1 especially the major ones1 possess the ,u-shaped cross section4 ,this feature can best be seen by looking down from the head of the valley rather than from the valley floor4 ,splendid examples are the ,swiftcurrent ,valley viewed from ,swiftcurrent ,pass or ,lookout2 ,st4 ,mary ,valley from east of ,logan ,pass2 the ,belly ,river ,valley from ,ptarmigan ,tunnel2 and ,cataract ,creek ,valley from ,grinnell ,glacier4 ,illustration3 ,,figure #a4 ,,idealized ,,sketch ,,of ,a ,,glacial ,,stairway ,,from ,,the ,,arete ,,at ,,the ,,center ,,of ,,the ,,range ,,to ,,the ,,ice ,,age ,,moraine ,,at ,,the ,,mouth ,,of ,,the ,,valley4 ,cirque wall ,glacier ,lake ,moraine ,the floors of many of the ,park's major ,u-shaped valleys instead of having a more or less uniform slope1 steeper near the head than farther down1 as is usually the case in a normal stream valley1 are marked by several steep drops or 8steps10 between which the valley floor has a comparatively gentle slope4 ,such a valley floor1 throughout its entire course1 is sometimes termed the glacial stairway4 ,most of the steps1 particularly those in the lower courses of the valleys1 are due to differences in resistance of the rocks over which the former ice flowed4 ,on the east side of the ,lewis ,range1 where the steps are especially pronounced1 the rock strata of which the mountains are composed dip toward the southwest1 directly opposite to the direction of the slope of the valley floors 7,figure #a74 ,thus1 as glaciers flowed from the center of the range down toward the plains1 they cut across the edges of these tilted rock layers2 where the ice flowed over weaker beds it was able to scour out the valley floor more deeply creating a 8tread0 of the glacial stairway4 ,the more resistant rock formations were less easily removed1 and the ice stream1 in moving away from the edges of these resistant strata1 employed its powers of plucking and quarrying to give rise to cliffs or 8risers40 ,lakes dammed partly by the resistant rock strata now fill depressions scoured out of the weaker rock on the treads 7,figure #a 74 ,these are rock-basin lakes1 and where several of them are strung out along the course of the valley they are referred to as paternoster lakes because their arrangement resembles that of beads on a string4 ,well-known examples of such bodies of water are ,swiftcurrent and ,bullhead ,lakes1 two of the long series which stretches for seven miles between ,many ,glacier ,hotel and ,swiftcurrent ,pass4 ,resistant layers in the lower portion of the ,altyn formation1 the upper part of the ,appekunny1 and the upper part of the ,grinnell#b normally create risers4 ,illustration3 ,,typical ,,glacial ,,valley ,,with ,,chain ,,of ,,rock-,,basin ,,lakes4 ,,glenn ,,and ,,crossley ,,lakes ,,in ,,distance2 ,,unnamed ,,lake ,,in ,,foreground ,,rests ,,in ,a ,,hanging ,,valley ,,and ,,its ,,outlet ,,drops ,,several ,,hundred ,,feet ,,to ,,the ,,main ,,valley 7,,hileman ,,photo7 ,the tributaries of glacial valleys are also peculiar in that they usually enter the main valley high above its floor and for this reason are known as hanging valleys4 ,the thicker a stream of ice1 the more erosion it is capable of performing2 consequently1 the main valley becomes greatly deepened1 whereas the smaller glacier in the tributary valley does not cut down so rapidly1 leaving its valley hanging high above the floor of the major valley4 ,the valleys of ,virginia and ,florence ,creeks1 tributary to the ,st4 ,mary ,valley are excellent examples of hanging valleys4 ,a splendid view of ,virginia ,creek valley may be had from ,going-to-the-,sun ,road near the head of ,st4 ,mary ,lake4 ,the valley above ,bird ,woman ,falls as seen from ,going-to-the-,sun ,road just west of ,logan ,pass is a spectacular illustration of a hanging valley4 ,in addition there are many others1 such as ,preston ,park1 on the trail from ,st4 ,mary to ,piegan ,pass2 and the ,hanging ,gardens near ,logan ,pass4 ,illustration3 ,,reynolds ,,mountain ,,at ,,logan ,,pass--,a ,,typical ,,horn ,even more conspicuous than the large ,u-shaped valleys and their hanging tributaries are the long1 sharp-crested1 jagged ridges which form most of the backbone of the ,lewis ,range4 ,these features of which the ,garden ,wall is one of the most noticeable1 are known as aretes and owe their origin to glaciers4 ,as the former long valley glaciers enlarged their cirques by cutting farther in toward the center of the range1 the latter finally was reduced to a very narrow steep-sided ridge1 the arete4 ,the imposing height of the ,garden ,wall can readily be determined by using the layer of diorite as a scale4 ,the conspicuous black band formed by the edge of this layer has an average width of #ge feet4 ,so1 from the porch of the ,many ,glacier ,hotel a ,park visitor can readily see that the ,garden ,wall1 even though five miles distant1 is about #d1bjj feet high4 ,the height of other aretes can be just as readily obtained1 for the band of diorite appears on the faces of most of them4 ,in certain places glaciers on opposite sides of the arete nearly cut through creating a low place known as a col1 usually called a pass4 ,gunsight1 ,logan1 ,red ,eagle1 ,stoney ,indian and ,piegan are only a few of the many such passes in the ,park4 ,at places three or more glaciers plucked their way back toward a common point leaving at their heads a conspicuous1 sharp-pointed peak known as a horn4 ,innumerable such horn peaks occur throughout both the ,lewis and ,livingstone ,ranges4 ,excellent examples near ,logan ,pass are ,reynolds1 ,bearhat1 and ,clements ,mountains4 ,other imposing horns are ,split ,mountain at the head of ,red ,eagle ,valley1 ,kinnerly ,peak in the ,kintla ,valley1 and ,mount ,wilbur in ,swiftcurrent ,valley4 ,the horn peak1 because of its precipitous sides1 is especially attractive to mountain climbers4 ,the comparatively recent dates of first ascents on many ,park peaks attest to the difficulties they offer the mountaineer4 ,mount ,wilbur1 despite proximity to ,many ,glacier ,hotel and camp1 was unclimbed until #aibc2 ,mount ,st4 ,nicholas succumbed in #aibf1 and the first ascent of ,kinnerly ,peak was made by several members of the ,sierra ,club in #aicg4 ,another feature of the ,park which must be attributed partly to glaciation is the waterfall4 ,there are two principal types1 one which occurs in the bottom of the main valleys and one at the mouth of the hanging tributary valleys4 ,the former1 exemplified by ,swiftcurrent1 ,red ,rock1 ,dawn ,mist1 ,trick1 ,morning ,eagle and others1 is located where streams drop over the risers of the glacial stairway4 ,in other words1 resistant layers of rock which the former glaciers were unable to entirely wear away give rise to this type of fall4 ,examples of the hanging tributary type of fall which is due directly to the activity of the glaciers are ,florence1 ,bird ,woman1 ,virginia1 ,grinnell1 ,lincoln1 and many others4 ,illustration3 ,,trick ,,falls ,,in ,,the ,,two ,,medicine ,,river ,no less conspicuous than the mountains themselves are the lakes4 ,in most instances glaciers have been either directly or indirectly responsible for the origin of the several hundred in the ,park4 ,in general1 these lakes may be divided into five main types1 depending upon their origin4 7#a7 ,cirque lakes4 ,this type of lake frequently is circular in outline and fills the depression plucked out of solid rock by a glacier at its source4 ,some of the most typical examples are listed in the foregoing discussion of cirques4 7#b7 ,other rock-basin lakes4 ,this type1 referred to above1 fills basins created where glaciers moved over areas of comparatively weak rock4 ,in all cases the lake is held in by a bedrock dam4 ,a typical example is ,swiftcurrent1 which lies behind a dam of massive ,altyn ,limestone layers4 ,the highway1 just before it reaches ,many ,glacier ,hotel1 crosses this riser of the glacier stairway4 7#c7 ,lakes held in by outwash4 ,most of the large lakes on the west side of the ,park fall in this category4 ,the dams holding in these lakes are composed of stratified gravel which was washed out from former glaciers when they extended down into the lower parts of the valleys4 ,lake ,mc,donald1 largest in the ,park1 is of this type4 ,illustration3 ,,st4 ,,mary ,,lake ,,from ,,goose ,,island ,,overlook 7#d7 ,lakes held by alluvial fans4 ,st4 ,mary1 ,waterton1 ,lower ,st4 ,mary1 and ,lower ,two ,medicine ,lakes belong in this group4 ,these bodies of water may have been rock-basin lakes1 but at a recent date on their history streams entering the lake valley have completely blocked the valley with deposits of gravel2 thus either creating a lake or raising the level of one already present4 ,st4 ,mary and ,lower ,st4 ,mary ,lakes probably were joined originally to make a lake #ag miles long4 ,more recently ,divide ,creek1 entering this long lake from the south1 built an alluvial fan of gravel where it entered the lake4 ,this fan was large enough to cut the lake into the two present bodies of water4 ,the ,st4 ,mary ,entrance ,station at the eastern end of ,going-to-the-,sun ,road1 is located on this alluvial fan1 the form of which can readily be distinguished from a point along the road at the north side of the upper lake near its outlet4 7#e7 ,moraine lakes4 ,most lakes with moraines at their outlets are partly dammed by outwash or rock ridges4 ,one of the prominent examples is ,josephine ,lake near ,many ,glacier ,hotel4 ,the moraine which is partly responsible for the lake is a hill which can be seen from ,many ,glacier ,hotel4 ,several of the large lakes on the west side of the ,park are also held partly or entirely by moraines4 ,another type of moraine lake1 which occurs only at ,sperry and ,grinnell ,glaciers1 has already been mentioned4 ,it differs from all other ,park lakes in having a glacier for part of its shoreline4 ,there are two of these lakes at ,sperry and one at ,grinnell4 ,despite their small size1 they are tremendously interesting1 not only because of their relation to the glacier1 but also because they are ordinarily filled with icebergs throughout the summer4 ,their surfaces often remain frozen until mid-summer4 ,there are several types of minor importance1 the principal one of which is that formed by a landslide damming the valley4 ,one cannot remain long in ,glacier ,national ,park without noticing the varying colors of its lake waters4 ,in fact this feature is so striking that ranger-naturalists probably are questioned more about it than about any other feature or phenomenon4 ,to find the answer we must go again1 as in so many instances1 to the glaciers4 ,as the ice moves it continually breaks rock fragments loose4 ,some of these are ground into powder as they move against each other and against the bedrock under the glacier4 ,most types of rock1 especially the limestones and shales on which the ,park glaciers rest1 when ground fine enough yield a gray powder4 ,all melt-water streams issuing from glaciers are cloudy or milky from their load of this finely ground 8rock flour40 ,water from ,grinnell ,glacier is so laden with rock flour that the small lake along the edge of the ice into which the water pours is nearly white4 ,much of the silt is deposited in this lake1 but enough is carried downstream to give ,grinnell ,lake a beautiful turquoise hue4 ,some of the very finest sediment which fails to settle in ,grinnell ,lake is carried a mile farther to ,josephine ,lake to give it a blue-green color4 ,even ,swiftcurrent ,lake1 still farther downstream1 does not contain clear water4 ,the rock flour which colors these as well as other ,park lakes can also be seen in the streams4 ,baring ,creek at ,sunrift ,gorge 7see p4 #ac in ,motorist's ,guide7 is milky with powdered rock from ,sexton ,glacier4 ,cataract ,creek along the trail between ,josephine and ,grinnell ,lakes is noticeably milky1 extraordinarily so in mid-afternoon on very warm days4 ,at such times melting of the glaciers is accelerated and more silt is then supplied to the streams4 ,part of ,sperry ,glacier1 in contrast to ,grinnell1 rests on a bright red shaly rock 7known to the geologists as argillite7 which yields a red-gray powder when finely ground4 ,hence the water in several small lakes adjacent to the glacier has a pinkish tint4 ,although a large number of ,park streams are fed by glaciers there are many others1 particularly in the south and west sections1 which have no ice as their source4 ,on a trail trip from ,sunrift ,gorge to ,virginia ,falls1 one is certain to be impressed by the extreme clarity of the water in ,virginia ,creek4 ,for half a mile below the falls the trail follows this cascading torrent from one crystal pool to another4 ,so clear is the water that we are apt to mistake for wading pools places where the water may be five or more feet deep4 ,snyder ,creek near ,lake ,mc,donald ,lodge nearly rivals ,virginia ,creek in clarity4 ,the sources of these two streams obviously are not melting glaciers4 ,from the foregoing discussion1 it is evident that glaciers constitute one of the principal controlling factors in the color of the water in ,park streams and lakes4 ,where there are no ice masses streams are clear1 and where glaciers occur the water possesses many shades varying from clear blue through turquoise to gray1 and in rare cases even pink4 ,illustration3 ,,moraine ,,near ,,grinnell ,,glacier ,,is #abj ,,feet ,,high4 ,,the ,,glacier ,,extended ,,nearly ,,to ,,top ,,of ,,moraine #ej ,,years ,,ago4 7,,dyson ,,photo7 ,although the former large glaciers of the ,ice ,age transported huge amounts of rock debris down the valleys of the ,park1 the moraines which they deposited are1 as a rule1 not conspicuous features of the landscape4 ,the ,going-to-the-,sun ,road1 however1 crosses several accumulations of moraine in which road cuts have been made4 ,the road traverses a number of such places along the shore of ,lake ,mc,donald4 ,because of the large proportions of rock flour 7clay7 in these accumulations1 the material continually slumps1 sometimes sliding onto the road surface4 ,one of these cuts has been partly stabilized by a lattice-like framework of logs4 ,the largest excavation in moraine along the highway is located about three miles east of ,logan ,pass just below the big loop where the road crosses ,siyeh ,creek4 ,the surfaces of many boulders in this moraine are marked by grooves and scratches1 imparted to them as they were scraped along the side of the valley by the glacier #aj1jjj or more years ago4 ,a small moraine is exposed along the exit road from the parking lot at ,many ,glacier ,hotel4 ,it contains a number of small red boulders1 the sources of which are the red rock ledges in the mountains several miles up the ,swiftcurrent ,valley1 plainly visible from the hotel4 ,one of these ancient moraines which has been eroded into a series of mounds 7#be to #ajj feet high7 extends from ,swiftcurrent ,cabin ,camp down the valley on the north side of the road to a point near the entrance to ,many ,glacier ,ranger ,station4 ,some of the cabins are actually situated in a space between two of the highest mounds4 ,illustration3 ,,looking ,,south ,,along ,,the ,,grinnell ,,glacier ,,ice ,,front4 ,,note ,,crevasses ,,along ,,which ,,bergs ,,are ,,breaking ,,off4 7,,dyson ,,photo7 ,surrounding all existing ,park glaciers are two sets of recent moraines varying in height from a few feet to more than two hundred4 ,so recently 7probably #hjj to #ijj years7 have the glaciers withdrawn from the older of these that only sparse willows and other forms of dwarf vegetation are growing on them4 ,the younger set of moraines1 which has accumulated during the last several hundred years1 consists of unweathered rock on which only small pioneer plants and lichens have begun to establish themselves4 ,these moraines are particularly striking at ,grinnell1 ,sperry1 ,blackfoot1 ,agassiz and ,sexton ,glaciers4 ,on the last few yards of the spectacular ,grinnell ,glacier trail all persons who make the trip to the glacier must climb over the moraine before setting foot on the ice4 ,from this vantage point on the highest part of this moraine the visitor can look down upon a huge crevassed mass of ice lying in a stupendous rock-walled amphitheater1 then merely by facing the opposite direction1 he will see unfolded before his view one of the most colorful vistas in the ,park4 ,more than a thousand feet below in the head of a splendid ,u-shaped valley lies the turquoise gem of ,grinnell ,lake4 ,a mile farther away the blue surface of ,lake ,josephine stands out in sharp contrast to the dark green of the spruce which lines its shores4 ,high above he can see the red summit of ,mount ,allen carrying its white snowbanks into the deep blue of a ,montana sky4 ,despite this magnificence the visitor must soon turn his attention to the tremendous accumulation upon which he stands1 for it is no less interesting than the mountains and lakes4 ,among the many boulders which lie along the path are two prominent limestone blocks each #aj to #ae feet in diameter4 ,the underside of one was grooved and polished as the ice pushed it across the rock surface underlying the glacier4 ,the other1 partially embedded in the moraine1 has a polished upper surface because the glacier flowed over it for a time4 ,both these boulders1 although now nearly #cjj yards from the ice front1 were covered by the glacier until about #bj years ago4 ,because of shrinkage many of the glaciers are no longer in contact with these newer moraines4 ,in some cases a quarter of a mile of bare rock surface intervenes between the moraine and the glacier which made it4 ,a few glaciers have disappeared within recent years1 but their moraines remain as evidence of former glacier activity4 ,one of the most notable examples is afforded by ,clements ,glacier1 a small body of ice which existed until about #aich in the shadow of ,clements ,mountain at ,logan ,pass4 ,its edge was bordered by a ridge-like moraine nearly a hundred feet high4 ,today1 the trail from ,logan ,pass to ,hidden ,lake skirts the outside edge of the moraine4 ,should the hiker leave the trail and climb the few yards to the top of this moraine he could see it stretched out before him as a giant necklace encircling the base of ,clements ,mountain1 but between mountain and moraine1 where a few years ago the glacier lay1 he will see only bare rock or drifted snow4 ,despite recent rapid shrinkage of glaciers and the disappearance of some1 ,glacier ,national ,park still is a land of ice1 yet when the visitor views its present day glaciers and its sublimely beautiful mountain scenery he should not be unmindful of the powerful forces which1 working during many thousands of years1 have brought it all about4 ,then1 and only then1 can he properly appreciate the magnificence which ,nature has so generously bestowed upon us4 ,illustration3 ,,clements ,,mountain ,,and ,,glacier4 ,,the ,,glacier ,,has ,,since ,,disappeared4 7,,hileman ,,photo7 ,,footnotes #a;,dr4 ,dyson worked as a ranger naturalist in ,glacier ,national ,park for eight different summers starting in #aice4 ,during that time he undertook special research on park glaciers in addition to his regular assignments4 #b;,for a brief description of these rock formations see ,special ,bulletin ,no4 #c 7,geologic ,story7 of the ,glacier ,natural ,history ,association4 ,,glacier ,,natural ,,history ,,association1 ,inc4 ,glacier ,national ,park ,west ,glacier1 ,montana ,organized for the purpose of cooperating with the ,national ,park ,service by assisting the ,interpretive ,division of ,glacier ,national ,park in the development of a broad public understanding of the geology1 plant and animal life1 history1 ,indians1 and related subjects bearing on the park region4 ,it aids in the development of the ,glacier ,national ,park library1 museums1 and wayside exhibits2 offers books on natural history for sale to the public2 assists in the acquisition of non-federally owned lands within the park in behalf of the ,united ,states ,government2 and cooperates with the ,government in the interest of ,glacier ,national ,park4 ,revenues obtained by the ,association are devoted entirely to the purposes outlined4 ,any person interested in the furtherance of these purposes may become a member upon payment of the annual fee of one dollar4 ,gifts and donations are accepted for land acquisition or general use4 ,illustration3 ,,glacier ,,natural ,,history ,,association ,,inc4 ,transcriber's ,notes --,silently corrected a few typos4 --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4