Permafrost

“ Ice forms, and every particle of water is swollen by the change. A strain is put upon the mineral particles against which the particles of ice crowd for more room. Frost is a very powerful agent in the crumbling of rocks, as well as of stubborn clods of earth. In warm climates, and in desert regions where there is little moisture in the rocks, this destructive action of freezing water is not known. In cold countries, and in high altitudes, where the air is heavy with moisture, its greatest work is done. ”

“ Once forced from their anchorage, the first storm that arises drifts them to sea, where the beautiful law which renders ice lighter than the warmest water, enables it to float, and drifts southward a vast magazine of cold to cool the tepid water which bears it along—the evaporation at the equator causing a deficit, the melting and accumulation of the ice in the frigid zone giving rise to an excess of accumulation, which tends, along with the action of the air and other causes, to institute and maintain the transporting current. ”

“ Ice formed in the atmosphere, and descending to the ground in the form of hail, often causes great destruction to vegetation and not infrequently to animal life. Where the frozen moisture reaches the earth as snow, it serves to protect rock, soil and vegetation from the effects of frost; but on sloping ground it is apt to give rise to destructive avalanches or landslips, while indirectly, by its rapid melting, it may cause serious floods in rivers. ”

“ The water in freezing expands, and in so doing pushes asunder the component particles of soil or stone, or widens the space between the walls of joints or crevices. When the ice melts the loosened grains remain apart ready to be washed away by rain or blown off by wind, while by the widening of joints large blocks of rock are detached from the faces of cliffs. Where rivers or lakes are frozen over the ice exerts a marked pressure on their banks; and when it breaks up large sheets of it are driven ashore, pushing up quantities of gravel and stones above the level of the water. ”

“ The use of clouds in the formation of rain, is too obvious to need pointing out more particularly. Snow is frozen vapour aggregated by a confused action of crystalline laws, and ice is water, solidified while in its fluid state, by the same crystalline forces. These are bad conductors of cold, and when the ground is covered with snow, or the surface of the soil, or if the water is frozen, the roots or bulbs of plants beneath are protected by the congealed water from the influence of the atmosphere, the temperature of which in northern winters, is usually very much below the freezing point ”

“ Here, when the sun reaches its summer height or a sweet-grass wind blows soft or a cloudburst above the peaks strikes the southerly face of the range, winter unfrocks in a single night. A glacier of snow melts within twenty-four hours into a torrent of lava and bursts with incredible fury from a thousand gorges.
When this happens nothing withstands. Whatever lies in the path of the flood is swept from the face of the earth. The mountains, assailed in a moment with the ferocity of a hundred storms, are ripped and torn like hills of clay. ”

“ The pressure, indeed, may be enormous, and portions of the ice be liquefied by it, but the water which is "ice-cold" escapes through innumerable fissures, and the freezing-point is not lowered by the pressure, as it would be if the water of liquefaction did not escape. The constant flowing of a glacier necessitates unceasing supply, and its source is found accordingly in that zone of elevation where snows accumulate. The snow-fall of which the glacier is born implies vapor clouds and condensation, and equally evaporation, the proximity of a warm climate and expanse of ocean. ”

“ The amount of precipitation being sufficient, the production of glaciers would depend upon temperature, which itself would be dependent upon local conditions, which again might, or might not, be due to elevation of land surfaces. His idea, in brief, was that while during the glacial epoch there might be over the entire globe a period of sufficient warmth to produce the desired evaporation, the precipitation would fall as rain or snow, according to the local uplift or depression. ”

“ During the winter this mass of ice is for the most part quiet, except that at the spring-tides of every month cracks and narrow lanes form, and then freeze rapidly again. Violent wind-storms will cause some disturbance in the ice, the pressure against the hummocks and ragged pinnacles of the large fields causing them to crush any thin ice before them and throw it up in ridges, thus leaving lanes or pools of open water behind, and causing a slow grinding, twisting motion of the pack, which, however, stops, and the open water freezes over, with the cessation of the wind. ”

“ But, under all these various circumstances, frost will transform the crystalline snow into more or less compact ice, the mass of which will be composed of an infinite number of aggregated snow-particles, very unequal in regularity of outline, and cemented by ice of another kind, derived from the freezing of the infiltrated moisture, the whole being interspersed with air. Let the temperature rise, and such a mass, rigid before, will resolve itself again into disconnected ice-particles, like grains more or less rounded. ”

“ Other things, such as stones, are melted only by terrific heat.
When the little particles of water that make up the clouds become very cold, they freeze as they gather and so make snowflakes. When the little particles of water in the air, that usually make dew, freeze while they are gathering on a blade of grass, we call it frost. When [pg 98] raindrops are carried up into colder, higher air while they are forming, they freeze and turn to hail. When snow or frost or hail or ice is heated, it melts and turns back to water. ”

“ The waste in sunshine must be enormous, while in dark weather rains and winds also melt the ice and add to the volume produced by the rain itself. The winds also, though in temperature they may be only a degree or two above freezing-point, dissolve the ice as fast, or perhaps faster, than clear sunshine. Much of the water caught in tight crevasses doubtless freezes during the winter and gives rise to many of the irregular veins seen in the structure of the glacier. ”

“ Evaporation goes on at all temperatures, even below freezing and from solid ice, its rate, of course, being diminished by low temperatures. At times, in spring or fall, the temperature of the air over rivers, when there is little wind, falls so far below the temperature of the water that the water vapor rising from the river by evaporation is quickly condensed in the form of fog, which may cover a part or all of the low contiguous land, checking radiation and preventing a further fall in temperature. ”

“ This heat the earth retained till evening. As the air chilled, the water-vapour from the warmer earth rose from its surface, and was arrested by the cold surface of the leaves. So cold was that surface that it froze the water-vapour when rising from the earth, and formed hoar-frost in very large quantities. When this happens later on in the season, one may be almost sure of having rain in the forenoon.
As hoar-frost is just frozen dew, I can even more surely convince you of the formation of hoar-frost as rising from the ground by observations made by me at my manse in Strathmore, in June 1892. ”

“ One may well account for the formation of the hailstone by assuming that its alternating layers of snow and ice are caused by the horizontal roll of a thunderstorm, the under part of which has a temperature at or above freezing and the upper half much below freezing. A raindrop is formed in the lower part, frozen in its course through the upper part, receives a fresh coating of water or snow with each revolution and a freezing before its circuit is completed. It thus gains in size until it becomes too heavy to be sustained by the whirling storm-cloud, when it falls to earth. ”

“ When one of the above-mentioned frosts occurs, the stone which composes the weir soon becomes incrusted with ice, which increases so rapidly in thickness as in a short time to impede the course of the stream, which falls over it in a tolerably uniform sheet, and with considerable velocity; at the same time, the wind blowing strongly from the north-west, contributes to repel the water and freeze such as adheres to the crest of the weir when its surface comes nearly in contact with the air. ”

“ Every winter ice thrusts its expansive wedge into each opening. Places are so shattered by this explosive action that thousands of gallons of water are admitted. This collects in openings, and the following winter the freezing and forcing continues. During the winter the irresistible expansion of freezing water thus pushes the rocks and widens the openings with a force that is slow but powerful. Winter by winter rocks are moved; summer by summer the water helps enlarge the opening. Years or centuries go by, and at last during a rainy time or in the spring thaw a mass slips away or falls over. ”

“ The average precipitation equals the evaporation. The heat that is absorbed and evolved in the process of lifting up and letting down such a body of water has a powerful influence upon climates as well as upon winds; it is the chief source of that motive power which gives to the winds their force, to the storm its violence. Six hundred and twenty pounds of aqueous vapour occupy in the open air the space which it takes one thousand pounds of dry air at the same temperature to fill. ”

“ As melting goes on, the marginal trough, or valley, grows deeper and wider, since both sides are being melted, the land side slower. The dead, protected ice in melting first sheds off the large boulders, as they are not able to lie on slopes where smaller ones can. Then the next larger ones are rolled off, and pebbles and sand in succession. Meanwhile this material is subjected to torrent-action, as if it were cast into a trough. When floods come it is carried forward and stratified, according to the force of the current, sand, mud, or larger material. ”

“ When the clouds are overcharged with moisture in cold climates or in cold weather, the vapour freezes as it condenses and forms snow, which under the microscope presents a series of the most beautiful star-like crystals (fig. 3) ; the same result is produced by the freezing of the vapour or fog near to the earth's surface, this is called "hoar-frost," which is (like dew) deposited on those parts of the surface most cooled by radiation. Hail is caused in all probability by the drops of rain passing through a cold stratum of air and becoming frozen as they fall. ”

“ In this case, the snow in the woods is absorbed as fast as it melts, by the soil it has protected from freezing, and does not materially contribute to swell the current of the rivers. If the mild weather, in which great snow-storms usually occur, does not continue and become a regular thaw, it is almost sure to be followed by drifting winds, and the inequality with which they distribute the snow over the cleared ground leaves the ridges of the surface-soil comparatively bare, while the depressions are often filled with drifts to the height of many feet. ”

“ The work of evaporation is of course not done by the atmosphere, though the atmosphere determines the effect of the solar energy which does the work. [25]
The precipitation is distributed with great inequality, and this inequality affects both the rain and the snow. Some regions have heavy precipitation and some light; some regions have much rain and little snow; others have much snow and little rain; others have rain and no snow, and still others have snow and little or no rain. ”

“ Powder snow acquires a crust if it is exposed to wind, to sun shining at a sufficiently direct angle, and to an air temperature above freezing. Wind alone has the power of forming crust without a preliminary melting of the surface. I do not know why this should be so, but no doubt the reason is to be found in the law that pressure lowers the freezing-point, so that the increased pressure caused by wind lowers the freezing-point, or, in other words, produces the effects of a thaw at the point where the [Pg 409] wind acts even though the general air temperature may be well below zero centigrade. ”

“ The conditions favorable to glaciation are, therefore, heavy precipitation and low annual temperature. If the precipitation is scanty, the small snowfall is soon melted; and if the temperature be too high, the moisture is precipitated not in the form of snow but as rain. It is important here to keep in mind that snow is a poor heat conductor and itself protects its deeper layers from melting. ”

“ Everybody will understand that moisture formed in hot tracts of the atmosphere has little chance of being converted into snow, and that, while a warm atmosphere may generate water—destructive of ice and snow surfaces—a very cold atmosphere cannot assist in glacier formation—on high land, at any rate—for want of vapours to condensate and precipitate, and for want of water masses to consolidate. ”

“ Experience will teach him that Lows from the southwest are reasonably sure of causing precipitation, and that if his temperature be sufficiently low—anywhere from zero to 20°—the fall will be in the shape of snow; that Lows that only skirt our northern border will be deficient in precipitation, even if they cause any at all; that the slow settling of a High over the South Atlantic States means heat for all the rest of the country east of the Rocky Mountains in degree that will be dependent upon the magnitude and the intensity of the southern High ”

“ The annual evaporation from the surface of the ice, which even in winter is never entirely interrupted during the severest frost, and the destruction of ice by the action of rain and waves, are balanced, to speak generally, by its re-formation by frost. The maximum accumulation of ice takes place in spring, its minimum in the beginning of autumn. We observed in the autumn of 1873 not only the evaporation of the snow of the preceding winter, but also a vertical decrease of ice of about four feet. ”