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During the Canada Winter Games (1971) more than 4000 cars were parked on the ice cover of Blackstrap Lake during the skiing events on Mount Blackstrap. The rapid increase in winter recreation activities will result in increased use of ice covers for sporting events and parking. Ice thickness and buoyancy measurements were made at regular intervals over the lot during the 3 weeks immediately prior to the Winter Games. Continuous recordings of the ice surface deflection were obtained in the critical loading area. Systematic loading trials of increased magnitude were carried out to measure the static and dynamic performance of the ice cover. During the Winter Games the design load distribution was adjusted daily so that it was equal of less than the observed buoyancy of the ice cover in the parking area. This load distribution was achieved by controlling the parking density. This criterion provides a conservative estimate of the allowable distributed load for loading periods of several hours duration.The procedures developed provide a reasonable guideline for the safe use of freshwater covers for similar events.

Standard deviations for lake breakup dates were calculated for all lakes in Canada with reasonably long breakup records and for five lakes in Wisconsin with long-term records. Standard deviations were about 13 days for coastal lakes and 7–11 days for continental lakes. The accuracy of the melting degree day method of predicting breakup dates were investigated for 12 of these lakes; standard deviations ranged from 3.3–8.0 days. Regression equations for predicting breakup dates were developed from past breakup and air temperature records for the 12 lakes; standard errors ranged from 1.6–4.3 days. General forecast guidelines were developed for application to lakes with limited breakup records. The equations and forecast guidelines are suitable only for continental lakes where wind and river inflow effects are not dominant.

There is no classification of river and lake ice that simultaneously takes into account the history of ice formation, the structure of the ice cover, and the texture of the various ice types. Such fundamental information is a prerequisite to the determination and discussion of their physical and mechanical properties.The first part of this classification is a brief description of the formation and the physical properties of the three important ice layers making up the ice cover. The second aspect of the classification deals with the texture of various ice types.It is possible to determine certain meteorological conditions which have occurred during formation of primary ice from on-site observations and the study of ice profiles. Hydrodynamic information can be obtained from the study of secondary or superimposed ice. Presently, major events causing layers of frazil slush, congealed frazil slush, and drained snow ice can easily be recognized and interpreted.The evaluation and eventual prediction of the mechanical properties of the various ice types according to such a classification will be helpful in solving engineering and navigation problems.

In this paper a study of lake ice at Peters Lake with respect to crystallographic nature and impurity in crystal grain boundaries is described. The appearance of the ice structure in 1962 was quite uniform over the whole area of the lake; it showed predominantly horizontal c-axes. Another type of ice with predominantly vertical c-axes could not be found even in the surface layer of the ice. The cause of these two types of ice is explained as being due to wind action. A correlation between the grain-size and the depth of ice is expressed in exponential form down to a depth of 100 cm. A linear relationship between the thickness of ice and the depth of snow cover was obtained. Impurity in grain boundaries measured as specific electrical conductivity was hard to detect in such a pure ice as that at the lake whose purity was about 1 micromho/cm. Supplementary data from Lake Nukabira, Hokkaido, are summarized and compared with the data from Peters Lake.

The coasts of Finland are fringed by vast and labyrinthine archipelagos, in which wooded islands with small hills obstruct visibility. This is a great hind-rance to topographical survey. On the other hand, conditions for carrying out hydrographic survey are excellent, as positions can be fixed on the basis of a rectangular lattice of lines run easily and accurately along the surface of the ice. There was in the past every encouragement to adopt this method of survey, as the coastal waters and the lakes in central Finland are ice-covered for some 5 months every year (from December to April) and in the northern parts of the country for an even longer period. It is true that the work is hindered by the cold, but in early spring (March and April) surveying can generally be carried out in satisfactory conditions.

Direct observations of the growth of ice on, and perpendicular to, a water‐air interface are described, in an experiment reproducing the conditions of formation of natural lake ice. The final, preferred crystal orientation is affected by the initial orientations and by selective wedging cut of grains of certain orientations, but often the most important factor is grain boundary migration. Boundary migration is driven in part by interfacial energy and probably in part by stress. The origin of the stress is not known. Preferred intergrain orientations are found.

Laboratory experiments and field observations permit an explanation of the varying crystallographic orientations observed in lake ice in terms of four factors: (1) coincidence of the plane of most rapid growth in ice (the basal plane) with the vector of thermal flux, (2) mechanical fragmentation of early-formed dendrites and plates by winds above a critical velocity (approximately 2.7 m./sec.), (3) the presence of a sufficiently thick layer of supercooled water to permit vertical crystal growth, and (4) the operation of geometric factors, first pointed out by Perey and Pounder, which result in the gradual elimination of the flatter plates of growing ice by the steeper ones.

Most adult sockeye salmon returning to Redfish Lake had spent two years in the ocean. Survival from smolt to returning adult at the lake ranged from 0.14 to 1.83%. The sex-ratio was nearly even. Survival of sockeye in the lake from potential egg deposition to smolt migration was usually less than 6%. In at least one year, smolts originating from kokanee and/or residual sockeye may have comprised a large proportion of the migration. There was little relationship between egg deposition and smolts produced. Sockeye salmon smolts migrated from Redfish Lake primarily from 1800 to 2400 hr. There was no consistent relationship between seasonal timing of the migration, lake ice cover, temperatures or flow of the outlet stream. The role of photoperiod in timing of the migration and the parr-smolt transformation is unclear. Growth of juvenile sockeye in the lake was inversely related to population density and age at migration was dependent upon first year growth in the lake. More than half the fish of a ye...

The morphology, physics, and chemistry of Lake Miers (78° 07′ S, 163° 54′ E), a warm freshwater Antarctic lake, are discussed. The presence of rock debris on the floating lake ice has led to the formation of dirt cones and melt pools. Fossil levels of these pools show that the annual ablation is 15–20 cm. Despite a mean annual air temperature of − 20 ° c, the bottom waters of the lake are at + 5 ° C. This is shown to be a natural example of solar heat storage and the observed temperature profile is satisfactorily accounted for. Chemical evidence suggests that the lake has been filled by freshwater containing K, Na, Cl, and O2 , and that it is now stagnant below the 4° C depth. In this lower zone Ca, Mg, CO2, and SiO2 are diffusing upwards from the lake bed, possibly partly released by anaerobic biological activity.

Intersecting minor ridges on the plain of glacial Lake Agassiz were probably pushed up by floating lake ice and apparently are not primarily the result of permafrost, wave action and running water, or a fracture pattern in the underlying bedrock, as previously suggested. Associated intersecting minor grooves were also formed by dragging lake ice. They are essentially identical to grooves forming in Great Slave Lake in recent times.

Two sets of curves are developed which can be used to forecast the dates of. 1) first appearance of ice in the fell; and 2) ice formation from shore to shore on the Mackenzie River at Fort Good Hope, Canada. Similar curves, based on the same method, can be derived for sheltered harbor, lake and river locations. The numerical constants necessary to develop these curves were obtained from a relationship between mean daily air temperatures and previously observed dates of ice formation. To apply the curves, an adjusted temperature record, based on a numerical constant (N) and daily air temperatures, is maintained starting in early summer. Subsequently, this daily-adjusted temperature is applied to the family of curves to provide a day-to-day forecast of the date of ice formation.

An examination of rates of ice growth, actual ice thickness and the quality of the lake ice profile on Knob Lake, central Labrador—Ungava, showed that all these factors were extremely variable. Three sites were established on Knob Lake from 1957 to 1961, and a similar sequence of sites was established on a neighbouring lake, Maryjo Lake, from 1959 to 1961. Significant variations occurred within a single lake body from site to site, though it was noted that certain patterns of ice growth and quality did occur throughout most years and could be directly related to patterns of snow accumulation on the lake. Variations from lake to lake were found to be least at the centre lake sites, probably because snow cover was always least at these sites and would not affect heat loss so greatly as at the marginal sites. It is suggested that the majority of empirical formulae proposed for lake ice growth are unrealistic for short-term forecasting of ice thickness and growth, and even long-term forecasting, using accumulated degree-days of frost, only gives average values. The only answer is repeated samplings on any lake, until such time that sufficient data are gathered for a full statistical approach based on probability analysis.

A device is described which gives direct measurements of the rates of accretion of ice on both the top and the bottom of lake ice without the necessity for repeated drilling. A method for measuring the hydrostatic water level is also described.

Striations indistinguishable from glacial striations are formed by boulders pushed shore-wards by lake ice. Thus striations alone do not provide unequivocal evidence for the direction of movement of continental ice sheets.

ON returning recently from North Wales, I was very pleased to meet with a description, by Mr. James C. McConnel (NATURE, December 27, p. 203), of the elaborate experiments performed by himself and Mr. Dudley A. Kidd on glacier and lake ice at St. Moritz. An experiment I had made on the ice of Llyn Creigenen, a small lake to the north-west of Tyrau Mawr, seems to me to be, in some measure, confirmatory of the results obtained in connection with the crystallization of lake ice.

Large grooves up to 33 m wide and 4760 m long have been inscribed in soft unconsolidated lake bottom sediments at Great Slave Lake, NWT. The grooves are probably formed by wind-driven ice floe gouging during each spring breakup. Smaller grooves having a boulder at one end were formed by boulders pushed by floating lake ice. Study of the hydraulics of fluid flow upon spheroidal solids indicates that wind is quite incapable of transporting large rocks like those suggested to have formed the grooves on Racetrack Playa, California.

In order to use the distribution of lake ice to analyze climate of a particular region, one must know which climatic factors are related to the freezing and thawing of lakes. The major goal of this study is to map the freezing and thawing of lakes in a particular region and to relate certain aspects of climate to these events. A second objective, which is actually a corollary to the primary objective, is to evaluate the effects of the morphology of lakes on their response to climate, and, after determining these effects, to examine the possibility of estimating mean depths of lakes remotely. The majority of investigations involving the interrelationship of lakes and climate have dealt with single lakes or, at most, lakes within a single region. To obtain a large scale regional picture of this interrelationship it was necessary to use aerial reconnaissance and remote sensing techniques. Since the detailed information that can be gathered when dealing with a single lake cannot be obtained in a regional study, the observations reported here must necessarily be more general in nature.

Data are reported on the sizes of clearings broken in a lake ice sheet 20 to 30 inches thick, as a result of each of 45 explosions. The charge weights varied from 1 to 42 lbs, and the charge positions varied from 20 ft below to 2 ft above the ice layer.

Effects of underwater explosions beneath lake ice and Arctic ice have been studied experimentally. Results are applicable to prediction of underwater damage ranges from nuclear bursts beneath ice, and to the design of an explosive ice destructor to provide nuclear submarines with quick access to surface.

Experimental studies of the propagation of elastic waves in lake ice were made at Lake Margrethe, Michigan, and Garrison Dam, North Dakota. These studies were designed to investigate, in particular, flexural waves in the ice‐water system produced by hammer drops, cylinder drops, and sledge hammer impacts on lake ice and nearby land. A method similar to the standard seismic‐refraction techniques was employed for the wave studies. Flexural wave dispersion curves obtained from records of mechanical impulses on ice are, in general, consistent with theoretical curves based on the “layer” theory of Press and Ewing (1951) for the observed ice thickness and elastic parameters. Three groups of points on the observed dispersion curves obtained from Lake Margrethe data are flexural waves with frequencies from 2 to 8 cps, 13 to 25 cps, and 40 to 140 cps. The first and third groups exhibit dispersion consistent with the combined thickness of a two‐layer floating ice sheet. The second group follows dispersion for a wave path in the upper thin layer only. Hammer drops on land generate flexural waves in the layer of frozen ground in the frequency range 15 to 40 cps. These waves are transmitted across the lake‐shore boundary and follow a wave path in the upper thin layer of lake ice. A continuous train of flexural waves in the frequency range 4 to 140 cps was observed on records of cylinder drops taken at Garrison Dam, North Dakota. (Parts of this work were supported by Tri‐service Contract No. DA‐36‐039‐sc‐52654.)

This paper reports the results of bending and shear tests made on ice from Lake Michigan and on artificial ice so frozen as to have the same crystal orientation. The bend specimens normally failed in tension with an indicated tensile strength of about 200 psi. A marked increase of tensile strength with decreasing temperature was indicated. The shear strength was found to be about 100 psi. No temperature coefficient for shear strength could be detected. Specimens of the ice were studied in polarized light. It was observed that the optic axes of the ice crystals were usually normal to the surface of refrigeration. The crystal diameters were usually less than one inch.

OF late years attention has not unfrequently been called to this singular structure in ice, of which a number of instances are collected by the Rev. G. F. Browne, in his valuable book on the “Ice Caves of France and Switzerland” (chap, xviii.) In August, 1865, I had the opportunity of examining in his company some of these curious caverns; and since then have been on the look out for other instances of this structure. In January, 1867, I found it very well exhibited on a pond in Cambridge, an account of which may be found in the Proceedings of the Cambridge Philosophical Society, Part IV. and (more briefly) in my “Alpine Regions,” pp. 94, 334. I again saw it last summer in a block of river or lake ice, which was brought on board a steamer at Christiansand (Norway) from an ice house. This block was about 8 inches thick. The prisms were rather irregular in form, the area of their ends varying from about a quarter of a square inch to one square inch, the sides being usually five or six in number. The prisms were at right angles to the planes of freezing, which were well marked.