On Bottom Ice1

V. Ya. Altberg.

The question of bottom ice has a long but strange history. For more than a hundred years this phenomenon has attracted the attention of many, in view of the role it plays in northern countries, and in view of the lack of success of attempts to explain satisfactorily its peculiar feature, namely the earlier freezing of water (at the bottom) that is farther removed from the source of cooling and located closest to the source of heating (ground heat). Fruitless disputes about the nature of this “paradoxical” phenomenon have been going on since long ago, and, strange as it may seem, have not ended even up to the present time2. Most surprising of all is the fact that, despite the extensive literature3, which testifies not only to scientific interest in this phenomenon but also to its great practical importance in general, especially in hydraulic engineering when utilizing the country’s water power, the question of its nature and of the very cause of its formation has not been moved from the dead point at which it remained for many decades. The reason for this is that, in the absence of quantitative and experimental data, the question was usually discussed only in terms of mere suppositions and unfounded guesses. In view, however, of the abundant observational material accumulated recently, a timely and urgent need arose for a fundamental reconsideration of the whole question, which I undertook after the Petrograd public self-government, in 19154, applied to the Main Physical Observatory for clarification of the nature of this phenomenon and allocated certain funds to it for this purpose.

Not considering it possible to dwell here1 on the history of the various interpretations of the nature of the phenomenon and of the fruitless disputes on this subject, I prefer to pass directly to the facts and experiments that reveal the true essence of the phenomenon, characterizing only in the most general terms the state of the question as it then stood.

Until very recently there predominated among us (while abroad it still predominates even now2) a view that ascribed the unusual appearance of ice on the bottom to the cooling of the latter, as a result of the supposed radiation of heat through the water. This idea, developed by Farquharson (Farquharson, 1844), independently of him by Assmann (Assmann, 1888), and then used by Barnes (H. Barnes3), was recognized by the well-known physicist Coblentz (Coblentz4) as “the most successful,” giving “the most probable” explanation of the phenomenon under consideration, and had long been invariably taken by engineers as the basis when designing those parts of hydraulic installations and water intakes whose operation was hindered by the formation of bottom ice. However, the practice of American water-supply systems revealed an unquestionably negative result from such constructions, thereby casting doubt on the correctness of the original idea.

I have already noted5 that this idea, based on an arbitrary assumption of water’s allegedly unusual transparency for certain categories of infrared waves, is fundamentally wrong and contradicts the factual data of experiment6; as a result, the explanation of bottom ice by means of thermal radiation from the bed could be called “successful and most probable” only by misunderstanding.

Facts and results of laboratory experiments and observations in nature.

The immediate impulse toward clarifying the nature of bottom ice was the case of the extraordinary freezing of the Neva not from above, as is usually the case, but from below (from the bottom), which occurred on December 14, 1914, when all of Petrograd found itself deprived of water owing to

freezing of the ends of water-intake pipes (in the form of flared openings, \(d = 2\) meters, with iron gratings), laid in the middle of the Neva on the bottom, at a depth of 20 m. According to divers’ testimony, the river bottom and all parts of the water-supply equipment located there were covered with a thick layer of loose ice, \(3/4\) meter thick. Similar cases have been repeated more than once, on a greater or lesser scale, not only in Petrograd, but also in a number of other cities of Russia and America (Warsaw, New York, etc.).

In January 1917, almost everywhere in England, the formation of bottom ice was observed, which entailed the suspension of water supply in a number of cities and districts.

However, hydraulic-engineering installations (power stations) experience much more frequent complications of this kind, especially in Canada, where they have to contend every year with the harmful manifestations of such ice. Grandiose formations of bottom ice, sometimes causing changes even in the rocky relief of river beds, occur on the large rivers of Siberia, especially on the Angara River.

The elucidation of the conditions for the formation of such ice was begun in a laboratory setting at the Main Physical Observatory, where it was soon possible to reproduce this phenomenon artificially and to determine the principal factors that cause it. Special attention was directed first of all to the thermal conditions, with the use of sensitive thermometers (accurate to \(0^\circ,002\)). It turned out that water cooled indoors by means of refrigerating mixtures, under the condition of continuous stirring, can easily be supercooled by several degrees below zero; whereas when cooled outdoors by contact of the stirred water with frosty air, provided that the smallest crystals are introduced from the atmosphere, it can never be supercooled as strongly as in the first case, though weak supercooling (measured in small fractions of a degree) could be established in all cases. Upon reaching a temperature of approximately \(-0^\circ,1\), very small and thin plates (scales), in the form of little disks 1–2 mm in diameter, ordinarily appeared in the water; these gradually increased in size and number. After this the temperature of the water gradually and slowly rose, without, however, attaining exactly \(0^\circ\), from which it differed by 2–3 thousandths of a degree. With such negligibly weak supercooling, the water (stirred in the frost) could remain for many hours, despite the continuous separation of scaly ice within the water and on the bottom of the vessel. Crystallization, consequently, takes place with the indispensable presence of supercooling, even if extremely weak. The structure of the ice plates (scales) formed within the water and on the surface of the bottom of the vessel proved to be identical—quite round, perfectly transparent plates with mirror-like parallel surfaces (Fig. 1).

Incidentally, the total heat loss of the water was determined, and it proved to be rather considerable: ordinarily it exceeded 1 gram-calorie per minute from a surface of 1 cm² (in frost exceeding 6° and in the presence of wind).

To clarify the conditions of formation of bottom ice in a laboratory setting, the first observations in natural conditions on the Neva River in 1916/17 and 1920/211 were organized with sufficient accuracy and thoroughness, with the aim of determining the temperature conditions in the river during the cooling period in general and, in particular, during the formation of bottom ice. For this purpose a staff of observers from the Main Physical Observatory was enlisted, who carried out observations under my direction.

The following instruments were used:

1) Mercury thermometers of the highest sensitivity (graduated to 0°.01), in special mountings with thermal inertia.

2) A Callendar electric thermograph, specially ordered from London (accuracy of measurement 0°.02).

3) A specially constructed instrument, by means of which it was possible to make quite reliable measurements of the water temperature directly in the river at any time of day or night, with an accuracy of 0°.002.

Fig. 1.

Fig. 2 presents a schematic section of the instrument.
T—sensitive thermometer, M—microscope, P—prism of total internal reflection, L—electric bulb, K—water-impermeable casing.

The determination of the corrections of all instruments and the measurements themselves in the river were carried out with all necessary and sufficient precautions.

Fig. 2.

We had at our disposal a steamer and a staff of divers. The receiver of the thermograph was placed at a depth of 12 meters, so that the instrument gave a continuous record of the temperature of the near-bottom layer of water. By means of thermometers, hourly observations (day and night) were made at various points of the river profile, both transverse and longitudinal. From the very extensive observational material thus obtained, only a summary of general conclusions can be presented here.

During the period when the temperature of the water is many degrees above 0°, its distribution over the profile can be regarded as uniform only in the roughest approximation. A more exact, systematic sounding revealed a rather variegated picture of the “microthermal” structure of the profile. Owing to the insufficiently thorough mixing of all layers in the river, it was usually possible to observe slight deviations of temperature in one direction or the other from its mean value, sometimes reaching 0°.3. These deviations (positive and negative) are distributed over the profile in the most capricious manner, without any regularity, often even contrary to the statically stable distribution of densities, so that lighter layers proved to be situated below denser ones. As the general temperature of the river approached 0°, the amplitude of the deviations gradually decreased, being measured already in hundredths of a degree; however, complete equalization of temperature was not attained even at 0°. Thus, direct temperature measurements established that several colder layers of water could be found lying below

warmer (and consequently denser) ones. It was then established that after the river had cooled to \(0^\circ\), the water sometimes proved to be slightly supercooled (by hundredths of a degree, and in very rare cases even by \(0^\circ.1\)). Supercooling of this order could be observed not only at the surface, but also in the intermediate layers, and likewise in the bottom layer; moreover, in the latter the supercooling could at times even exceed that in the other layers.

In Fig. 3, by way of example, the course of the water temperature in the Neva from December 2–5 and 8–9, 1920, is given from hourly observations over the course of full days.

From this curve it is evident that the water temperature was almost all the time equal to \(0^\circ.00\), except on December 3, 5, and 8, when for several

Fig. 3.

hours it proved to be several hundredths of a degree above or below \(0^\circ\). During these very same periods, each time, the formation of bottom ice and, in general, of scale-like ice was also observed. It is curious to note that the supercooled state persisted for many hours, despite the presence of ice in the water and even despite the continuous formation of new portions of ice. From numerous series of observations over a number of years it was possible to draw the conclusion that, for the appearance of bottom ice and its more or less rapid growth, the indispensable presence of a supercooled state was required, even if only exceedingly slight, and that this state had to be maintained while the ice was being deposited.

Thus, as regards the very fact of the supercooling of water, the order of its magnitude, and, finally, the possible preservation of such a state in the presence of the solid phase, and even the unconditional necessity of ...

its significance for the process of crystallization, observations in nature stood in full agreement with the results of experiments in a laboratory setting.

The question of supercooling had to be taken up in such detail in order to resolve it exhaustively, in view of the fact that precisely with regard to it erroneous notions prevailed, amounting to an invariable denial of the very possibility of such an effect in a river, on the basis of the known fact that supercooling is destroyed after the introduction of a solid phase. Such an insufficiently well-founded generalization of a fact that occurs only under certain conditions (in the laboratory) to cases with entirely different conditions (in nature) led to incorrect ideas, which have, since the time of Gay-Lussac and up to the present, substantially hindered clarification of the essence of the phenomenon.

When I had only just begun to study the phenomenon of bottom ice, some of the leading representatives of the commission formed in 1915 specifically to study this phenomenon, doubting the possibility of supercooling in a river, even removed the very question of it from the program under discussion “in view of the dubiousness of the effect and its scant study.” When, however, direct observations nevertheless revealed this effect, the report on these observations stated that it was not the water that was supercooled, but that the instruments themselves had cooled below \(0^\circ\), while the temperature of the water was \(=0^\circ\) (L. A. Yachevsky, Hydrological Bulletin, 1915, No. 4). It may still seem unclear in what way the supercooled state is maintained for a long time (over the course of many hours) in the presence of a solid phase and even with the continuous release of new portions of ice. Until this circumstance was actually clarified, many expressed bewilderment and doubt as to its possibility, in view of the fact that even the first portions of separated ice should, in their opinion, have destroyed the very weak supercooling that existed.

Direct measurements, however, showed that, contrary to doubts, the supercooled state is not destroyed, and crystallization not only does not cease, but sometimes proceeds with even sufficient energy.1

The point is that an important factor, which in the present case is decisive, was usually overlooked. This is the general heat loss of the water, which determines the entire process of ice formation in general. It is known (according to Homen’s determination) that in cold autumn weather bodies of water lose large quantities of heat. Referred to a unit of surface (1 sq. cm), this heat loss may amount to 1 gram-calorie per minute, with which determinations of the heat loss of water in experiments with artificial reproduction of ice (under identical conditions) also agree.

With so powerful a heat loss from the surface, the temperature of the water nevertheless always remains approximately the same throughout the entire depth. This points to the equal participation of all layers in the heat loss, and also to the fact that heat transfer between all layers is effected easily and rapidly as a result of the thorough mixing of all layers during the turbulent motion of the water in the river. With convective heat transfer thus facilitated, and in view of the magnitude of the total heat loss, the latent heat released, for example, in the bottom region cannot here be retained and accumulated, but, being carried away through all the layers of water into the air, contributes to the prolonged preservation of the supercooled state, thereby maintaining conditions favorable for crystallization1.

Although what has already been set forth above is sufficient to clarify the essence of the phenomenon, I also wished to carry out an experiment reproducing the primary layer of bottom ice under conditions leaving no doubt that radiation is not only not the primary cause of this phenomenon, as Barnes believes, but that it may occur quite independently of it, and, on the other hand, that it is not caused by ice being brought down from the surface, as Altken asserts. To this end I set up a simple experiment for the formation of bottom ice under conditions guaranteeing the absolute impossibility both of ice being brought down from the surface and of any participation of radiation from the bottom. The arrangement of the experiment was as follows.

Fig. 4.

A glass vessel with water, a screen \(c\), and stones \(bb\) on its bottom (Fig. 4) was placed for one or two days in a room with a constant temperature of approximately \(-0^\circ.1\). After a piece of ice was introduced through tube \(d_2\), the water was stirred for some time with stirrer \(e\) and then left at rest. Soon it was possible to observe, on the surface of the stones, first the appearance of individual elements of ice, then an increase in their size, and subsequently a mass overgrowing of the stones with a layer of loose ice, as if with moss, while the water remained in a calm state (see the photograph, Fig. 5).

Thus, the artificial formation of a primary layer of bottom ice under conditions fully excluding both the bringing down of ice from the sur—

surface, as well as the participation of thermal radiation from the bottom, gives a direct indication of the direction in which the cause of the phenomenon should be sought.

And in the case of rivers, the mechanism of formation of the primary layer on the bottom is apparently the same as in its artificial reproduction.

On the basis of many years of experience gained from observations of bottom ice in nature and from the phenomenon reproduced many times in a laboratory setting, the essence of the phenomenon seems to me entirely clear, giving rise to no doubt and no longer containing any element of paradox.

Fig. 5.

At least, on the basis of my experience, in the overwhelming majority of cases I have been able to foresee in advance whether or not the given phenomenon would occur, and also to determine the conditions of the place and time of its occurrence. In the particular case of the Neva, the causes of the historical instances of the formation of bottom ice are perfectly clear to me, as are, in general, the causes of the rarity of the phenomenon in some bodies of water and, conversely, of its frequency in others.

In the light of the new facts obtained experimentally in the laboratory setting and by means of observations in nature, it is now not difficult to answer the question posed as early as the first half of the last century and now arising again because it has remained without a satisfactory answer up to the present time: why, in rivers, ice sometimes forms on the surface and sometimes on the bottom.

The English authors of the review on the present state of the question of bottom ice also raise a new question concerning the reason for the rarity of this phenomenon in certain bodies of water, in particular for Lochrutton (in southern Scotland)—only one case of freezing of the water conduit during the entire 45 years of its existence, despite the fact that there had been winters much more severe and prolonged than 1917. To this I could add, from the history of the Petrograd water supply, two comparatively rare cases of the grand formation of bottom ice, on December 8, 1894, and December 14, 1914, which entailed the cessation of the water supply for all of Petrograd.

An analysis of the entire aggregate of conditions under which both historical cases occurred leads to the conclusion that the cause here is only a rare coincidence, occurring only in the two years mentioned, of exceptionally favorable circumstances that ensured an especially powerful heat loss by the river, whose surface suddenly found itself deprived of the ice cover that usually forms under such weather conditions and that ordinarily protects the water to a significant degree from intense cooling. In both cases the sudden exposure of the river occurred during heavy ice drift, as a result of the strong formation of an ice jam in the river somewhat above the section within which, in the subsequent period (during the night), the entire bed of the Neva proved to be covered with a thick layer of ice. The meteorological conditions at that time were very favorable (low air temperature, −11° and −8°, with a sharp wind and a clear night sky) for producing the strongest heat loss by the water. Under these conditions, and taking into account the river’s full preparedness for the separation of ice, caused by prolonged ice drift in the preceding period, in the water—slightly supercooled throughout its mass down to the bottom—ice must have formed in the form of small elements, generally speaking everywhere, but predominantly at the bottom, where they could remain in place themselves and also retain (owing to regelation) other ice particles formed in masses within the water.

The heat loss of water depends to the greatest degree, besides meteorological factors, on the state of its surface (whether exposed or covered with ice, which excellently protects against strong heat loss). It is not for nothing that all observers unanimously testify to the absence of ice on the surface at the time when it forms on the bottom. No one, however, attached special significance to this extremely important circumstance, and no attention was paid to its role.

Moreover, it should be noted that an exposed surface, by causing strong heat loss, promotes the formation (other things being equal) of much larger quantities of bottom ice than of ordinary surface ice, a circumstance that observers likewise invariably note.

On the other hand, it is known that those sections of a river which remain exposed throughout the entire winter (for example, in rapids) are, if one may put it so, laboratories of bottom ice, which later, rising to the surface, accumulates in large quantities beneath the surface ice over tens of kilometers in the form of thick layers of loose ice (slush) 5–8 meters thick1.

Thus, the decisive factor for the formation of bottom ice is the presence of the maximum heat loss of the water, possible only in the absence of ice on the surface. In view of the fact that the concurrence of favorable circumstances ensuring a very great heat loss usually occurs rarely, outstanding cases of the formation of bottom ice likewise occur only infrequently. Therefore such cases must be very rare in England, with its mild climate. On the contrary, in Siberia, with its severe climate and fast-flowing rivers, the necessary conditions are ensured every year, as a result of which bottom ice forms there in large quantities annually (for example, on the Angara) and is classed among ordinary phenomena. Supercooling of the water is also a necessary condition, but by no means a sufficient one, since the very first portions of the ice being formed would release latent heat in an amount sufficient to eliminate the supercooling. Therefore decisive importance is acquired by factors capable of continuously maintaining such a state, despite the formation of ice and, together with it, the release of latent heat.

The facts obtained by experiment and observation, accompanied by exact measurements, together with the long-established fact of the complete opacity of water (in great thicknesses) to waves corresponding to the supposed radiation of the river bottom, make all earlier and modern conjectures about the nature of the phenomenon, which had been regarded as paradoxical, either superfluous or wholly unacceptable; this applies in particular to the explanation by radiation, which, simply by misunderstanding, is still considered in America the most probable even now.

In England Aitken2, although he rejects the possibility of the formation of bottom ice by radiation, nevertheless substantiates this differently, namely by the impossibility, in his opinion, of water passing into the solid state without a prior strong supercooling of the water by several degrees. In view of the obvious impossibility of such strong cooling of the water at the bottom, he does not admit the very possibility of the formation of ice on the bottom in situ and, like Gay-Lussac, explains its appearance there by transport from the surface, where it is formed in direct contact with the source of cooling. Direct experiments have shown, however, that for water to pass into the solid state there is by no means required so strong a cooling as Aitken thought; that for this, on the contrary,

sufficient even with negligible supercooling, provided that there is a seed in the water (which under natural conditions is fully ensured by the constant introduction of ice particles from the frosty air). In view of the untenability, therefore, of Aitken’s initial premise, his explanation becomes unfounded and, moreover, superfluous.

Now, after the clarification of all the conditions for the formation of bottom ice, one cannot help being surprised that so simple and natural a phenomenon could for so long have been regarded as mysterious and even, in the words of some, a “mysterious phenomenon of nature,” concerning whose nature the most perverse conjectures and suppositions were expressed.

Explanations that only seemed probable, but were in fact unfounded, strange as it may be, were accepted as truths from ancient times up to the very most recent period. Yet the practical applications of such worthless teachings (chiefly in America) invariably led to definite negative results.

Experiments and observational facts, having rejected all artificial explanations and fantastic interpretations, now make it possible to replace them with a simple and transparently comprehensible explanation, in full agreement with what is known about the transition of matter from one state to another.

1. M. F. Tsionglinskii. On observations of the freezing of the Neva River and studies of ice jams on it. St. Petersburg, 1905. ↩↩↩↩↩↩

2. I. Aitken. l. c. ↩↩↩

3. H. Barnes, Anchor-Ice Formation from the Standpoint of the Radiation Theory, New-York, 1906. ↩↩

4. W. Coblentz, Investigations of Infra-Red Spectra, Carnegie Institution of Washington Publ. No. 97, p. 147. 1908. ↩↩

5. Proceedings of the Main Physical Observatory, vol. 3, 1921. ↩

6. According to the investigations of Raschen, Rubens, Aschkinass, K. P. Yakovlev, and others, water does not possess such transparency in the infrared part of the spectrum; on the contrary, precisely in the region corresponding to the radiation of a cold body (the river bed), it absorbs extremely strongly, absorbing all the energy already in the thinnest layers of water, measured in small fractions of a millimeter. ↩