# Encyclopædia Britannica, Ninth Edition/Lake

See also Lake on Wikipedia; Lake in the 11th edition; and the disclaimer.
Distribution of Lakes.—Although there are few countries where lakes are entirely absent, still it requires little study to see that they are much more thickly grouped in some places than in others. Of the larger lakes, for instance, we have the remarkable group in North America, which together form the greatest extent of fresh water in the world. A similar group of immense lakes is found in Central Africa:—Lakes Victoria Nyanza and Albert Nyanza, whose overflow waters go to form the Nile; Lake Tanganyika, at the source of the Congo; and Lake Nyassa, on a tributary to the Zambesi. In Asia the largest fresh water lake is Lake Baikal, on the upper waters of the Lena. All these freshwater lakes of great size are at the sources of large and important rivers; the salt lakes in which Asia also abounds are at the mouths of large rivers, as the Caspian at the mouth of the Volga, and Aral Sea at the mouth of the Oxus.
Passing from the consideration of these larger lakes, which from their size may be considered inland oceans, and which therefore necessarily occur in small number, we find large numbers of lakes of comparatively small dimensions, and when we consider them attentively we find that they are reducible to a small number of species, and, as in the case of plants and animals, the distribution of these species is regulated chiefly by climate, but also by geological conditions. Perhaps the most important and remarkable species of lakes is that to which the Scottish lakes belong. They are generally characterized by occupying long narrow depressions in the valleys of a mountainous country in the neighbourhood of the sea, and in a temperate climate. On the sea-coast, lakes of this character are found in Norway, Scotland, Newfoundland, Canada, the southern extremity of South America, and the south end of the middle island of New Zealand; somewhat removed from the sea we have the Alpine lakes of Switzerland and Tyrol, and the great Italian lakes, all of which display the same features as those of Scotland or of Norway. In many flat countries lakes are extraordinarily abundant, as for instance in the north part of Russia and Finland, in the southern part of Sweden, in the northern parts of Canada, and on a small scale in the Hebrides.
Lagoons, found on all low sandy coasts, owe their origin to the shifting of the sand under the influence of the wind and tide. They are found at the mouths of large rivers, as on the Baltic and at the mouth of the Garonne.
In volcanic regions lakes are not uncommon, generally of a more or less circular form, and either occupying the site of extinct craters or due to subsidences consequent on volcanic eruptions; such are the Maare of the Eifel in Germany, and many lakes in Italy and in the Azores.
Lakes are not only widely distributed in latitude and longitude, they also occur at all elevations. Indeed, as a certain elevation above the sea produces an effect as regards climate equivalent to a certain increase of latitude, we find lakes existing in the centre of continents, and on high plateaus and mountain ranges, in latitudes where they would be speedily dried up if at the level of the sea. Many of the lakes in Scotland (as Lochs Lomond, Morar, Coruisk), of Norway, of British Columbia, and of southern Chili are raised only by a few feet above the level of the sea, and are separated from it often by only a few hundred yards of land, while in the Cordilleras of South America we have Lake Titicaca 12,500 feet, and in Asia Lake Kokonor 10,500 feet above the sea. Many lakes whose surface is raised high above the level of the sea are so deep that their bottom reaches considerably below that level.
Dimensions of Lakes.—The principal measurements connected with a number of lakes in different parts of the world, presented in the following table, will give a more precise idea of the size of the lakes than could be given by description alone:—
| Name of Lake. | Mean Lati- tude. | Mean Lati- tude. | Mean Lati- tude. | Length. | Length. | Length. | Breadth (Max.). | Breadth (Max.). | Breadth (Max.). | Depth (Max.). | Height in Feet above the Sea of | Height in Feet above the Sea of | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. |
| Name of Lake. | Mean Lati- tude. | Mean Lati- tude. | Mean Lati- tude. | Length. | Length. | Length. | Breadth (Max.). | Breadth (Max.). | Breadth (Max.). | Depth (Max.). | Surface. | Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. | Tempera- ture of Water at Bottom. |
| | | | | Miles. | Miles. | Miles. | Miles. | Miles. | Miles. | Feet. | | | ° F. | ° F. | ° F. | ° F. | ° F. | ° F. | ° F. |
| Superior | 47° | 45′ | N. | 350 | | | 100 | | | 978 | 627 | −351 | 38·8 | 38·8 | 38·8 | 38·8 | 38·8 | 38·8 | 38·8 |
| Michigan | 44° | | N. | 320 | | | 80 | | | 840 | 594 | −246 | ... | ... | ... | ... | ... | ... | ... |
| St Clair | 42° | 30′ | N. | 18 | | | 22 | | | 20 | 570 | +550 | ... | ... | ... | ... | ... | ... | ... |
| Erie | 42° | | N. | 220 | | | 48 | | | 204 | 564 | +360 | ... | ... | ... | ... | ... | ... | ... |
| Titicaca | 16° | 30′ | S. | 90 | | | 30 | | | 924 | 12,500 | −11,576 | 54·6 | 54·6 | 54·6 | 54·6 | 54·6 | 54·6 | 54·6 |
| Kokonor | 37° | | N. | 91 | | | 42 | | | ... | 10,500 | ... | ... | ... | ... | ... | ... | ... | ... |
| Baikal | 53° | | N. | 330 | | | 40 | | | 4,080 | 1,360 | −2,720 | ... | ... | ... | ... | ... | ... | ... |
| Balkash | 46° | | N. | 280 | | | 25 | | | 238 | 72 | +166 | ... | ... | ... | ... | ... | ... | ... |
| Caspian | 42° | | N. | 600 | | | 50 | | | 3,600 | −85 | −3,685 | 44·6 | 44·6 | 44·6 | 44·6 | 44·6 | 44·6 | 44·6 |
| Dead Sea | 31° | 30′ | N. | 45 | | | 10 | | | 1,308 | −1,272 | −2,580 | ... | ... | ... | ... | ... | ... | ... |
| Tanganyika | 6° | | S. | 330 | | | 40 | | | 1,000 | 2,700 | ... | ... | ... | ... | ... | ... | ... | ... |
| Como | 46° | | N. | 48 | | | 2 | · | 5 | 1,356 | 670 | −686 | ... | ... | ... | ... | ... | ... | ... |
| Geneva | 46° | 25′ | N. | 45 | | | 8 | · | 7 | 1,092 | 1,218 | +126 | 41 | · | 7 | to | 43 | · | 5 |
| Constance | 47° | 40′ | N. | 35 | | | 8 | | | 394 | 1,300 | +906 | 39·6 | 39·6 | 39·6 | 39·6 | 39·6 | 39·6 | 39·6 |
| Lomond | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 20 | | | 4 | | | 630 | 25 | −605 | 41 | · | 4 | to | 42 | | |
| Morar | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 11 | | | 1 | · | 5 | 1,020 | 30 | −990 | 40 | · | 8 | to | 41 | · | 4 |
| Ness | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 23 | | | 1 | · | 3 | 774 | 50 | −724 | 41 | · | 2 | to | 42 | · | 4 |
| Lochy | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 10 | | | 1 | | | 480 | 93 | −387 | 42 | | | to | 44 | | |
| Katrine | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 7 | | | 0 | · | 8 | 480 | 364 | −116 | 41·4 | 41·4 | 41·4 | 41·4 | 41·4 | 41·4 | 41·4 |
| Tay | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 14 | · | 5 | 1 | | | 450 | 390 | −60 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 |
| Rannoch | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 14 | · | 5 | 1 | | | 378 | 668 | +290 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 | 43·9 |
| Ericht | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 14 | · | 5 | 0 | · | 8 | 330 | 1,153 | +823 | 44·7 | 44·7 | 44·7 | 44·7 | 44·7 | 44·7 | 44·7 |
| Tummel | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 2 | · | 5 | 0 | · | 5 | 120 | 450 | +330 | 45·5 | 45·5 | 45·5 | 45·5 | 45·5 | 45·5 | 45·5 |
| Garry | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ | 56° to 57° 30′ N. | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ | 2 | · | 5 | 0 | · | 3 | 102 | 1,330 | +1,228 | 53·9 | 53·9 | 53·9 | 53·9 | 53·9 | 53·9 | 53·9 |
From this table it will be seen that by far the largest continuous sheet of fresh water is the group of North American lakes, and of these Lake Superior is more than double the size of any of the others; this is principally due to its great breadth, as it is very little longer than Lake Michigan. Lake Superior communicates with Lakes Michigan and Huron, which are really branches of one and the same lake, by the St Mary’s river, the fall being 49 feet from Superior to Huron. Huron empties itself into Erie by the St Clair river, Lake St Clair, and finally the Detroit river. Lake Erie overflows by the Niagara river and falls into Lake Ontario, whence the water finally is conveyed to the sea by the St Lawrence. The area of the lakes together is in round numbers 100,000 square miles, and, if that of the St Lawrence and its estuary be added, the water area will be about 150,000 square miles, while the whole drainage area is only 537,000 square miles. Hence of the water conveyed by the St Lawrence to the sea, rather more than one-fourth falls on the surface of the water itself. Looking to their great extent, we should have suspected them to be much deeper than is found to be the case. The deepest, Lake Superior, is no deeper than Loch Morar in Inverness-shire. Comparatively shallow, however, as they are, the bottoms of them all, with the exception of Erie, are several hundred feet below the level of the sea. It has been supposed that in former times this chain of lakes formed an arm of the sea similar to the Baltic in Europe, and in support of this view we have the fact of the discovery of marine forms in Lake Michigan.
A former connexion with the ocean is claimed for a number of the Swiss and Italian lakes by Dr Forel and Professor Pavesi, and the Norwegian lakes by Loven and Sars, on the ground of the occurrence of marine forms of the crustaceans and other classes. For a summarized account of these researches see Pavesi, Arch. de Genève, 1880, iii. 1.
Temperature of Lakes.—The earliest reliable temperature observations in lakes or seas are those of Saussure, and they are to be found in his charming Voyage dans les Alpes. He was the first to obtain thoroughly trustworthy observations in the deeper waters of the lakes. He used for this purpose an ordinary thermometer whose bulb was covered over with several thicknesses of cloth and wax, so as to render it very slowly conducting. He was in the habit of leaving it down fourteen hours, and then bringing it up as quickly as possible and immediately reading the temperature. He did not, however, trust to his thermometer not changing its reading while being brought up, but by an elaborate series of experiments he obtained corrections, to be applied when the thermometer had to be drawn through more or less water of higher temperature. His observations are collected in the following table along with those of Jardine in some of the Scottish lakes, at the beginning of the century:—
| Name of Lake. | Name of Lake. | Date. | Temperature of | Temperature of | Depth. | Height above Sea. |
| Name of Lake. | Name of Lake. | Date. | Surface. | Bottom. | Depth. | Height above Sea. |
| | | | ° F. | ° F. | Feet. | Feet. |
| Geneva | | February. | 42·1 | 41·6 | 1,013 | 1,230 |
| Neuchâtel | | 17th July. | 73·7 | 41·4 | 346 | 1,304 |
| Bourget | | October 1784. | 64·0 | 42·1 | 256 | ... |
| Annecy | | 14th May 1780. | 57·9 | 42·1 | 174 | 1,426 |
| Joux | | ... | 55·6 | 51·3 | 85 | 350 |
| Bienne | | ... | 69·3 | 44·4 | 231 | 1,419 |
| Constance | | 25th July 1784. | 64·6 | 39·6 | 394 | 1,250 |
| Lucerne | | 28th July. | 68·4 | 40·8 | 640 | 1,380 |
| Thun | | 7th July 1783. | 66·2 | 41·0 | 373 | 1,896 |
| Brienz | | 8th July 1783. | 68·0 | 40·5 | 533 | ... |
| Maggiore | | 19th July 1783. | 78·1 | 44·1 | 357 | ... |
| Lomond | | 8th Sept. | 59·5 | 41·5 | 600 | 25 |
| Katrine | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,$ | 7th Sept. 1812. | 57·3 | 41·0 | 480 | 364 |
| Katrine | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,$ | 3d Sept. 1812. | 56·4 | 41·3 | ... | ... |
An exceedingly important and valuable series of observations was made by Fischer and Brunner in the Lake of Thun throughout the course of a whole year (March 1848 to February 1849). They used, after Saussure’s method, thermometers protected by non-conducting envelopes, which were pulled up as quickly as possible. The depth of the water where they observed was 540 feet, and they made a series of observations of the temperature at that depth, at the surface, and at eleven intermediate depths, and repeated the series of observations at eight different dates over the year. From these series, which afford the first information of the yearly march of temperature at different depths, we learn that the lake as a whole gains heat till the end of September, then loses it until the month of February, when it begins to warm again, though slowly. The maximum temperature occurs in October at depths from the surface to 70 feet, in November at depths from 70 to 120 feet, in December from 120 to 200 feet, and in February at 500 feet. As the whole yearly variation of the temperature at 200 feet is less than a degree, the epoch at which the greater depths attain their maximum and minimum temperatures cannot be certainly deduced from one year’s observations. The minimum temperature of depths from the surface to 80 feet is attained in the month of February, at greater depths in the month of March. During the course of the whole year the temperature at the bottom varied between 40°·7 and 40°·9 Fahr., and in the month of February the whole of the water from the surface to the bottom was between 40°·7 and 41° Fahr.
These and other observations showed that, from depths of 400 feet, the variation of temperature with increasing depth is quite insignificant, so that even though the lake might be 1000 feet deep the temperature at 400 feet is only one or two tenths of a degree different from that of the bottom; further, on many of the thermometers recently used, it is impossible to distinguish with certainty temperatures differing by less than half a degree, consequently it was not difficult to believe that in all deep lakes there is a considerable stratum of water which remains constantly at the same temperature, all the year and every year, and that in winter this stratum thickens so as often to fill the lake, and gets thinner again in summer. By the improvement of the instruments both of these suppositions have been shown to be erroneous. In summer and in temperate latitudes, however deep the lake may be, its temperature falls as the depth increases, first rapidly and then very slowly, and the bottom temperature observed in any summer depends on the nature of the winter which preceded it, and may vary from year to year by one to two degrees. It was also believed that the deep water of a lake preserved constantly the mean winter temperature or the mean temperature of the six coldest months of the year in the locality. This was deduced from some observations by Sir Robert Christison in Loch Lomond, who found the bottom temperature at Tarbet to be 41°·4 Fahr., agreeing with the mean of the six winter months as observed at Balloch Castle, which, however, is about 15 miles distant. Although the theorem may be accidentally true for Loch Lomond, it has been proved not to hold for other lakes. Thus Simony (Wien. Sitz. Ber., 1875, lxxi. p. 435) gives the following table, comparing the temperature of the bottom water in the Gmünder See with the winter (October to March) air temperature:—
| | Winter Period. Mean Temperature. | Winter Period. Mean Temperature. | | Summer Period. Mean Temp. | Bottom Temp., Gmünder See. | Date of Observation of Bottom Temperature. |
| | Oct.–Mar. | Dec.–Feb. | | Summer Period. Mean Temp. | Bottom Temp., Gmünder See. | Date of Observation of Bottom Temperature. |
| | ° F. | ° F. | | ° F. | ° F. | |
| 1867–68 | 37·5 | 32·9 | 1868 | 64·4 | 40·5 | 6th Oct. 1868. |
| 1868–89 | 40·1 | 36·8 | 1869 | 63·1 | 40·5 | 1st Oct. 1869. |
| 1869–70 | 35·0 | 29·3 | 1870 | 60·8 | 40·2 | 26th Sept. 1870. |
| 1871–72 | 35·2 | 27·8 | 1872 | 62·2 | 40·0 | 3d Oct. 1872. |
| 1872–73 | 41·0 | 35·0 | 1873 | 60·2 | 40·5 | 5th Oct. 1873. |
| 1873–74 | 39·0 | 32·7 | 1874 | 61·9 | 40·4 | 25th Sept. 1874. |
| 1874–75 | 33·8 | 28·2 | ... | ... | 39·1 | 10th April 1875. |
It will be seen that, with the exception of the end of 1872, the mean winter temperature is below that of the bottom water, and generally very markedly so.
| | Loch Ness. | Loch Ness. | Culloden. | Culloden. | Loch Lochy. | Loch Lochy. | Corran. | Corran. |
| | Surface. | Bottom. | Oct. to March. | Nov. to April. | Surface. | Bottom. | Oct. to March. | Nov. to April. |
| 1877 | 53·0 | 42·4 | 40·2 | 40·0 | 55·0 | 44·0 | 42·3 | 40·8 |
| 1878 | 59·0 | 42·3 | 41·6 | 40·9 | 61·0 | 43·7 | 42·7 | 42·5 |
| 1879 | 51·4 | 41·2 | 37·2 | 35·8 | 54·0 | 42·0 | 38·9 | 37·5 |
| 1880 | 57·0 | 42·4 | 41·0 | 40·8 | 57·6 | 43·8 | 42·0 | 41·9 |
| 1881 | 53·1 | 41·45 | 36·1 | 36·2 | 54·0 | 42·25 | 38·6 | 38·7 |
From this table it is apparent that the bottom temperature, even of lakes as deep as Loch Ness, is subject to considerable variation from year to year, that it depends on the temperature of the previous winter, and that it is usually higher than that temperature. The difference between the bottom temperature and the mean winter temperature is greater the lower the winter temperature is. It is further interesting to notice that the mean winter temperature of 1878–79 was about one degree higher than that of 1880–81, yet the bottom temperatures were 0°·25 lower in 1879 than in 1881, and this is no doubt due to the fact that the cold of 1878–79 was more continuous than that of 1880–81, when the actual temperatures observed were much lower. The temperature of the bottom water depends not only on the temperature of the previous winter, and on the depth of the lake; it also depends on the nature of the country where it lies, and especially on its exposure to winds. Winds drive the surface water before them, and if there were no return current it would be heaped up at the further end. The effect is to accumulate surface water at one end, and to draw on deeper water to make up the deficiency at the other end. Hence the prevailing direction of the wind impresses itself on the distribution of temperature in the water; and this is well shown in the distribution of temperature as determined from observations at five stations on the same day in Loch Ness in a summer after a warm winter, and in one after a cold winter. In Scotland, warm weather is associated with southerly and westerly winds, and cold weather with northerly and easterly winds. In the warm years we have accumulation of surface water at the north-eastern end, and of bottom water at the south-western end, producing in summer a higher mean temperature of water at the north-east, and a lower mean temperature of water at the south-west end. In cold years the reverse is observed. Thus in 1879, after a cold winter, the mean temperature of the first 300 feet of water at the south-west end of Loch Ness was 48°·8, and at the north-east end 44°·96, a difference of nearly four degrees. In 1880, after a comparatively mild winter, it was 48°·13 at the south-west end, and 47°·95 at the north-east end, or nearly identical temperatures. Even at stations a few hundred yards from each other, great differences are often observed in the temperatures observed at the same depth, and it is evident that the difference of density so produced must cause a certain amount of circulation. There can be but little doubt that, under the influence of the varying temperature of the seasons, and of the winds, the water of a lake is thoroughly mixed once a year. In lakes which do not consist of a single long trough like Loch Ness, but of several basins as Loch Lomond, the bottom temperature is different in the different basins, even when the depth is the same. Loch Lomond consists of three principal basins of very unequal depth:—the large expanse of water studded with islands at the lower end, the Balloch basin; the middle or Luss basin; and the upper and deepest or Tarbet basin. In the last we have 600 feet of water, in the Luss basin 200 feet, and in the Balloch basin a maximum of 72 feet of water. On 23d September 1876 the bottom temperature in the Tarbet basin was 41°·4, and in the Luss basin 46°·4. Loch Tummel, a much smaller lake, consists of three basins, each of them being from 100 to 120 feet deep, and in them we have bottom temperatures of 46°·3, 46°·9, and 45°·2, the lowest temperature being nearest the outlet.
It might have been expected that the bottom temperature in lakes similar as regards size and depth would be lower at greater elevations and higher nearer the sea-level. This does not, however, hold universally; thus Lochs Tummel and Garry are very similar in size and depth; they are only 12 miles from each other, but Loch Tummel is 450 feet and Loch Garry 1330 feet above the sea; yet at 102 feet in Loch Garry the temperature on the 18th August 1876 was 53°·9, and in Loch Tummel at the same depth on the 16th August 1876 it was 45°·4. The difference of elevation is nearly 900 feet, and, instead of the higher lake holding the colder water, its water is 8°·5 warmer than that of the lower one. Similarly in Loch Ericht, 1153 feet above the sea, the bottom temperature at 324 feet was 44°·7, and in Loch Rannoch, 668 feet above sea, at the same depth it was 44°·0. These examples will suffice to show that many circumstances concur in determining the temperatures of the waters of lakes. There is one factor which is often neglected, namely, the amount of change of water. This depends on the drainage area of its tributary streams, and necessarily varies greatly.
The extent to which this circulation affects the deeper waters of a lake depends on local circumstances, and generally we may say that the more confined a lake is the more easily will it freeze, and the higher will be the mean temperature of its waters. In the very cold winter 1878–79 the writer was able to make observations on the temperature of the water under the ice in Linlithgow Loch and in Loch Lomond. In the following winter, which, though mild in Scotland, was excessively severe in Switzerland, Dr Forel made observations in the Lakes of Morat and Zürich, confirming the writer’s observations of the unexpectedly low temperature of the water. The freezing of so deep a lake as that of Zürich was a fortunate circumstance, because in it the bottom is actually at the temperature of maximum density. The majority of the lakes which freeze are so shallow as to admit of the whole of their water being cooled considerably below the temperature of maximum density.
The distribution of temperature in frozen lakes will be apparent from the table given below. Of the Lakes of Zürich and Morat and Loch Lomond the mean temperatures are in the order of their depth. Linlithgow is altogether peculiar. Its high temperature, which increased steadily all the time it was covered with ice, was due to chemical action amongst the filth which has been allowed to accumulate at its bottom. When the ice broke up the dead fish were taken away in carts.
Dr Forel gives the following particulars about the frozen Swiss lakes. “The Lake of Morat has a surface of 27·4 square kilometres and a maximum depth of 45 metres (147 feet); it is 1425 feet above the sea; and its mean latitude is 49° 56′ N. The ice overspread its whole surface suddenly in the night of the 17th to the 18th December, and it remained frozen till the 8th March. The Lake of Zürich has a superficies of 87·8 square kilometres, a maximum depth of 468 feet and altitude of 1338 feet, and a mean latitude of 47° 16′ N. Its congelation was gradual, and not sudden like that of the Lake of Morat. First the upper part of the lake was covered with ice between Männedorf and Wädensweil. At the end of December, the 28th, the ice covered it entirely, but only for a single day. On the 29th it thawed, and the lake remained partially free of ice until the middle of January. It froze over completely on the 22d January, and on the 25th the ice was 4 inches thick in the centre of the lake.” Of the larger Swiss lakes, Morat, Zürich, Zug, Neuchâtel, Constance, and Annecy were frozen in 1880; Thun is known to have been frozen four times, namely, in 1363, 1435, 1685, and 1695; Brienz has only once been frozen, in 1363; Lucerne freezes partially in very severe winters, and Geneva in its western and shallower part, whilst Wallenstadt and Bourget are not known to have ever been frozen.
Table of Temperatures in Frozen Lakes.
| Depth (in feet). | Depth (in feet). | Temperature in Degrees Fahr. | Temperature in Degrees Fahr. | Temperature in Degrees Fahr. | Temperature in Degrees Fahr. | Temperature in Degrees Fahr. |
| Depth (in feet). | Depth (in feet). | Zürich, 25th Jan. 1880. | Morat, 23d Dec. 1879. | Lomond, 29th Jan. 1879. | Linlithgow. | Linlithgow. |
| Depth (in feet). | Depth (in feet). | Zürich, 25th Jan. 1880. | Morat, 23d Dec. 1879. | Lomond, 29th Jan. 1879. | 11th Jan. 1879. | 25th Jan. 1879. |
| | 3 | ... | ... | 33·00 | 35·90 | 36·00 |
| | 6 | ... | ... | 33·50 | 36·30 | 36·80 |
| | 18 | ... | 35·06 | 33·95 | 36·90 | 37·80 |
| (Bottom) | 48 | 36·95 | 36·14 | 35·20 | 39·85 | 42·05 |
| (Bottom) | 65 | 37·25 | 36·30 | 36·30 | ... | ... |
| | 100 | 37·76 | 36·68 | ... | ... | ... |
| (Bottom) | 150 | 38·39 | 37·04 | ... | ... | ... |
| | 200 | 38·66 | ... | ... | ... | ... |
| | 300 | 38·84 | ... | ... | ... | ... |
| (Bottom) | 435 | 39·20 | ... | ... | ... | ... |
| Mean | | 38·40 | 36·00 | 34·46 | 37·22 | 38·28 |
For further information on the temperature of frozen lakes, see Buchanan, Nature, March 6, 1879; Forel, Arch. de Genève, 1880, iv. 1; Nichols, Proc. Boston Soc. of Nat. Hist., 1881, xxi. p. 53.
The curves traced by the gauge at Geneva have been subjected to a preliminary harmonic analysis by Professor Soret, and he has decomposed them into two undulations, the one with a period, from crest to crest, of seventy-two minutes, and the other with a period of thirty-five minutes, or a little less than half the larger period. As the amplitudes of the composing curves vary much, there is great variety in the resultant curves. Besides these two principal components, there are others which have not yet been investigated.
With regard to the cause of the phenomenon, Dr Forel attributes the ordinary seiches to local variations of atmospheric pressure, giving an impulse the effect of which would be apparent for a long time as a series of oscillations. The greater seiches, such as those of 1·5 metres, he attributed to earthquake shocks; but, as a very sensible earthquake passed over Switzerland quite recently without leaving the slightest trace on the gauge, he has abandoned this explanation, and is inclined to attribute them to pulsation set agoing by violent downward gusts of wind, especially at the upper end of the lake. M. Plantamour, who has devoted much attention to the same subject, assured the writer, in the summer of 1881, that he was completely at a loss for a satisfactory explanation of them.
Seiches have not been observed on the Scottish lakes, though there is little doubt that they would be found if sought for. There are, however, records of disturbances of some of the lakes, especially in Perthshire, of which the following may be cited as an instance.
A violent disturbance of the level of Loch Tay is reported in the Statistical Account of Scotland (1796), xvii. p. 458, to have occurred at Kenmore on 12th September 1784, continuing in a modified degree for four days, and again on 13th July 1794. Kenmore lies at the north-eastern end of the lake, where the river Tay issues from it. It lies at the end of a shallow bay. “At the extremity of this bay the water was observed to retire about 5 yards within its ordinary boundary, and in four or five minutes to flow out again. In this manner it ebbed and flowed successively three or four times during the space of a quarter of an hour, when all at once the water rushed from the east and west in opposite currents, . . . . rose in the form of a great wave, to the height of 5 feet above the ordinary level, leaving the bottom of the bay dry to the distance of between 90 and 100 yards from its natural boundary. When the opposite currents met they made a clashing noise and foamed; and, the stronger impulse being from the east, the wave after rising to its greatest height, rolled westward, but slowly diminishing as it went, for the space of five minutes, when it wholly disappeared. As the wave subsided it flowed back with some force, and exceeded its original boundary 4 or 5 yards; then it ebbed again about 10 yards, and again returned, and continued to ebb and flow in this manner for the space of two hours, the ebbings succeeding each other, at the distance of about seven minutes, and gradually lessening, till the water settled into its ordinary level. During the whole time that this phenomenon was observed the weather was calm. On the next and four succeeding days an ebbing and flowing was observed nearly about the same time and for the same length of time, but not at all in the same degree as on the first day.”
The above is the account given by the Rev. Thomas Fleming, at the time minister of Kenmore, who was an eye witness. It resembles in all essential particulars the descriptions of waves which accompany actual earthquakes, yet in his account he goes on to say—“I have not heard (although I have made particular inquiry) that any motion of the earth was felt in this neighbourhood, or that the agitation of the wave was observed anywhere but about the village of Kenmore.” It is well known that there were great seismic movements observed in Perthshire at the time of the Lisbon earthquake, and there is a tradition in the neighbourhood that Loch Lubnaig near Callander was largely increased in extent by the dislocations which took place.
As might be expected, in salt lakes which have no overflow, the yearly rise and fall is often considerable. In the Great Salt Lake in Utah, the greatest depth of which is 56 feet, changes of level are accompanied by great changes in water surface, and also in saltness of water. In the rainy season the Dead Sea stands 10 or 12 feet higher than in the dry season. The following table shows the chemical composition of the waters of various salt lakes, that of the sea-water in the Suez Canal being added for comparison:—
* ↑ Mém. Soc. Phys. Genève, xii. p. 255.
* ↑ These air temperatures are those of the observatory at Vienna, corrected for difference of level.
| | | Kokonor Sea. | Kokonor Sea. | Kokonor Sea. | Aral Sea. | Aral Sea. | Aral Sea. | Caspian Sea. | Caspian Sea. | Caspian Sea. | Caspian Sea. | Caspian Sea. | Caspian Sea. | Urumieh Sea. | Urumieh Sea. | Urumieh Sea. | Dead Sea. | Dead Sea. | Dead Sea. | Van Sea. | Van Sea. | Van Sea. | Suez Canal, Ismailia. | Suez Canal, Ismailia. | Suez Canal, Ismailia. |
| | | Kokonor Sea. | Kokonor Sea. | Kokonor Sea. | Aral Sea. | Aral Sea. | Aral Sea. | Open. | Open. | Open. | Karabugas. | Karabugas. | Karabugas. | | | Urumieh Sea. | Urumieh Sea. | Urumieh Sea. | Dead Sea. | Dead Sea. | Dead Sea. | Van Sea. | Van Sea. | Van Sea. | Suez Canal, Ismailia. | Suez Canal, Ismailia. | Suez Canal, Ismailia. |
| Specific gravity | Specific gravity | 1 | · | 00907 | ... | ... | ... | 1 | · | 01106 | 1 | · | 26217 | 1 | · | 17500 | ... | ... | ... | 1 | · | 01800 | 1 | · | 03898 |
| Percentage of salt | Percentage of salt | 1 | · | 11 | 1 | · | 09 | 1 | · | 30 | 28 | · | 5 | 22 | · | 28 | 22 | · | 13 | 1 | · | 73 | 5 | · | 1 |
| Name of Salt. | Name of Salt. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. | Grammes Salt in 1000 Grammes Water. |
| Bicarbonate of | lime | 0 | · | 6804 | 0 | · | 2185 | 0 | · | 1123 | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 0072 |
| ,, ,, | iron | 0 | · | 0053 | ... | ... | ... | 0 | · | 0014 | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 0069 |
| ,, ,, | magnesia | 0 | · | 6598 | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 4031 | ... | ... | ... |
| Carbonate of soda | Carbonate of soda | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 5 | · | 3876 | ... | ... | ... |
| Phosphate of lime | Phosphate of lime | 0 | · | 0028 | ... | ... | ... | 0 | · | 0021 | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 0029 |
| Sulphate of | lime | ... | ... | ... | 1 | · | 3499 | 0 | · | 9004 | ... | ... | ... | 0 | · | 7570 | 0 | · | 8600 | ... | ... | ... | 1 | · | 8593 |
| ,, | magnesia | 0 | · | 9324 | 2 | · | 9799 | 3 | · | 0855 | 61 | · | 9350 | 13 | · | 5460 | ... | ... | ... | 0 | · | 2595 | 3 | · | 2231 |
| ,, | soda | 1 | · | 7241 | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 2 | · | 5673 | ... | ... | ... |
| ,, | potash | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 5363 | ... | ... | ... |
| Chloride of | sodium | 6 | · | 9008 | 6 | · | 2356 | 8 | · | 1163 | 83 | · | 2840 | 192 | · | 4100 | 76 | · | 5000 | 8 | · | 0500 | 40 | · | 4336 |
| ,, | potassium | 0 | · | 2209 | 0 | · | 1145 | 0 | · | 1339 | 9 | · | 9560 | ... | ... | ... | 23 | · | 3000 | ... | ... | ... | 0 | · | 6231 |
| ,, | rubidium | 0 | · | 0055 | ... | ... | ... | 0 | · | 0034 | 0 | · | 2510 | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 0265 |
| ,, | magnesium | ... | ... | ... | 0 | · | 0003 | 0 | · | 6115 | 129 | · | 3770 | 15 | · | 4610 | 95 | · | 6000 | ... | ... | ... | 4 | · | 7632 |
| ,, | calcium | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 0 | · | 5990 | 22 | · | 4500 | ... | ... | ... | ... | ... | ... |
| Bromide of magnesium | Bromide of magnesium | 0 | · | 0045 | ... | ... | ... | 0 | · | 0081 | 0 | · | 1930 | ... | ... | ... | 2 | · | 3100 | ... | ... | ... | 0 | · | 0779 |
| Silica | Silica | 0 | · | 0098 | ... | ... | ... | 0 | · | 0024 | ... | ... | ... | ... | ... | ... | 0 | · | 2400 | 0 | · | 0761 | 0 | · | 0027 |
| Total solid matter | Total solid matter | 11 | · | 1463 | 10 | · | 8987 | 12 | · | 9773 | 284 | · | 9960 | 222 | · | 7730 | 221 | · | 2600 | 17 | · | 2899 | 51 | · | 0264 |
This table embraces examples of several types of salt lake. In the Kokonor, Aral, and open Caspian seas we have examples of the moderately salt, non-saturated waters. In the Karabugas, a branch gulf of the Caspian, the Urumieh, and the Dead Sea we have examples of saturated waters containing principally chlorides. The Van Sea is an example of the alkaline seas which also occur in Egypt, Hungary, and other countries. Their peculiarity consists in the quantity of carbonate of soda dissolved in their waters, which is collected by the inhabitants for domestic and for commercial purposes. The chemical reader will be struck by the quantity of magnesia salt dissolved in water which contains so much carbonate of soda. The analysis in the table is by Abich, quoted by Schmidt in his interesting “Études Hydrologiques,” published in the Bulletin de l’Académie de St Petersbourg. Another analysis by De Chancourt, quoted by Bischof, omits all mention of sulphate of magnesia, but inserts the carbonate.
The limits of this article do not admit of the discussion of the many interesting phenomena connected with salt lakes. With regard, however, to a former connexion of the Caspian with the Black Sea, which has been so often suggested, it seems improbable, both on chemical and on physical grounds, that they were ever connected as seas, that is, in the same way as the Black Sea is connected with the Mediterranean; but, if we consider the topography of the Caucasus district, we see that the lowest summit level of the land between the two seas is in the Manytsch valley, 86 feet above the Black Sea. Were the climate of the Caspian to change only very slightly for the moister, its waters might easily rise the 196 feet which would enable it to overflow towards the Mediterranean, while a relapse towards dryness would be followed by the retreat of the waters, which would be then confined as they are now to the basin of the sea. It is important, therefore, to bear in mind that no terrestrial dislocations are required to produce enormous changes in the level of salt lakes; we require only changes of climate, and these very slight. There can be little doubt that, if the climate of the Black Sea extended across the isthmus to the Caspian, the latter would now stand 200 feet higher, would be fresh, and would overflow into the Sea of Azoff. For other aspects of the subject see Geology.
(J. Y. B.)