Palestine Exploration Fund - Quarterly Statement for 1894/On the Depth and Temperature of the Lake of Tiberias

by Palestine Exploration Fund

 

ON THE DEPTH AND TEMPERATURE OF THE LAKE OF TIBERIAS.

By M. Th. Barrois.

{From the Reports of the sittings of the "Société de Géographie," Nos. 17-18, 1893.)

One of the principal objects of the long journey which I made in Syria during the summer of 1890, was the study of the deep fauna of this lake. Up to that time scarcely anything was known of it except the molluscs, and especially the fish, and the considerable number of these last caused it to be anticipated that waters so swarming with fish would harbour a rich population of inferior animals. These anticipations have not been deceived, but this is not the place to narrate the zoological results of my researches; let it suffice me to say that, thanks to a special kind of dredge, I have been able to study with much care the bathymetric distribution of the organisms which live in the lake. This study promised to be especially interesting in the great depths described by Lortet (820 feet), and by Macgregor, after Armstrong (935 feet). Now, these depths I have never been able to find, although for six days I traversed the lake in every direction, carrying my researches principally towards the points which M. Lortet himself kindly indicated to me before my departure from France.

Reluctantly I had to abandon my soundings, promising myself to clear up the question on my return. This has not been easy, and has demanded on the one hand long bibliographical researches, on the other a whole correspondence with Messrs. Armstrong and Lortet. The problem is not yet quite elucidated, but I think I have reduced it to its lowest terms, and a few casts of the lead will be sufficient to settle it definitely. In my efforts to explain it I have had occasion to notice several errors which little by little have been credited, and which it is necessary to cause to disappear from science. A few words of history are necessary in order to state properly the facts of the question.

In the month of August, 1847, Lieutenant Molyneux, of the English navy, succeeded by dint of great efforts in conveying a boat from Haifa to Tiberias;^[1] for two days he navigated the Lake of Gennesaret, occupying himself with topography and hydrography. Then the daring explorer, abandoning himself to the current of the Jordan, descended the river as far as the Dead Sea, which he likewise studied from the hydrographical point of view. Unfortunately, Molyneux had been so exhausted by the unhealthy and torrid climate of the Ghôr,^[2] that he died almost immediately after having rejoined his ship at Beyrout, before having been able to put in order the materials which he had collected. This death was so much the more regrettable that the observations of Molyneux on the depth of the Lake of Tiberias—to speak only of the subject which occupies us—constituted the first scientific documents collected on the question; they have also remained the only ones until to-day, as we shall see.^[3]

Replying by precise facts to the old legends, which were prevalent as to the considerable depth of the Lake of Tiberias, Molyneux, by a series of soundings made in all directions, demonstrated that in no part did the depth of the lake exceed 120 to 156 feet, or 36^m·55 to 47^m·55.

Lieutenant Lynch, who, the following year, at the head of an American mission, performed exactly the same journey as Molyneux, descending like him the Jordan as far as the Dead Sea, only crossed over the Lake of Tiberias at the southern mouth of the river, deferring until his return the hydrographic observations which he proposed to make there.^[4] As too often happens, these projects were never put into execution, and the American expedition re-passed the lake without stopping there. In his account. Lynch limits himself to saying that the greatest known depth of the lake is 27·5 fathoms or 165 feet (50^m·30). This number is evidently inspired by the observations of Molyneux; only in consequence of a typographical error they have printed 165 instead of 156, inverting the order of the two last figures.

Some years later Van de Velde's large map, "Map of the Holy Land," appeared; in the Lake of Tiberias is shown a series of fifteen soundings, varying from 10 fathoms (60 feet, or about 18 metres) to 26 fathoms (156 feet, or about 47 metres); these soundings, Van de Velde himself tells us,^[5] have been reported after Molyneux. In the face of the frankness of this indication, above all in the presence of the stated fact that Lynch never made a single cast of the lead in the Lake of Tiberias, it is difficult to

explain the error into which Macgregor has fallen when he writes, "My Map VII represents the Lake of Tiberias reduced by the pantograph to the scale of half-an-inch, after a photograph of the unpublished map of the Ordnance Survey, drawn up by Sir C Wilson and Major Anderson in 1866... The soundings are in feet after Van de Velde, who borrowed them from Lynch."^[6]

Macgregor does not appear to be very familiar with bibliographic researches, for a little further on (p. 369, note 2) he relates at fall length how Lynch in spite of his desire was not able to make the least sounding in the Lake of Tiberias. He says besides as much of Molyneux (p. 422), who, he asserts, did not examine the lake, but passed at once southwards to begin the Jordan.

Naturally there resulted from these badly digested readings a whole series of confusions, of which the following extracts will give an example:—

Sometimes the lake would have a depth of 156 feet (Map No. VII, facing p. 338, "Rob Roy"; this is the number of Molyneux);

Sometimes of 165 feet (p. 369); this is Lynch's number;
Sometimes of 160 feet (p. 423?);
Sometimes lastly of 936 feet (p. 363) or of 156 fathoms (p. 424), which is the same thing.

This last number, so different from the others, is given only in the seventh edition of 1886: we will see further on the origin and the explanation of it.

In short, no traveller since Molyneux had made the least sounding in the Lake of Tiberias, when there appeared in 1883 the excellent work of Lortet,^[7] who spent long days on this beautiful sheet of water, going over it and dredging it in every direction, in order to study its icthyological fauna. Without undertaking soundings properly so-called, this able naturalist in the course of his dredgings collected some interesting observations on the nature and the depth of the bottom which he explored: "The depth of the lake, which is inconsiderable, is on an average scarcely more than 50 to 60 metres; however, towards the middle of the large north basin I have several times dredged at depths of 250 metres without the line showing any sensible drift."

The passage from Macgregor, which I quoted above, based on a communication from Mr. Armstrong, seemed to come to the support of this assertion: the depth ascertained in 1886 is 936 feet.^[8] Also, before my departure for Syria I bad asked M. Lortet for the fullest information as to the exact site of these great depths, intending to explore them from the zoological point of view with much care. According to the directions which the learned Dean of the Faculty of Medicine of Lyons willingly gave me, my researches were to be especially carried on in the northern portion of the basin, in a line with the Wady Semakh and facing the northern mouth of the Jordan: it is, in fact, in the axis of the river that I found—in accordance with Molyneux—the most considerable depth.

But in spite of the most patient endeavours I found it impossible to discover the depths described by Lortet; in vain I traversed in every direction the northern portion of the lake, crossing and recrossing my line of soundings, the lead never marked more than 42 metres.

These soundings were made according to six principal axes:—

1st. From Tiberias to the northern mouth of the Jordan;
2nd. From Tiberias to Wady Fik;
3rd. From Hammam to Wady Semakh;
4th. From the northern mouth to the southern mouth of the Jordan;
5th. From the northern mouth of the Jordan to Wady Semakh;
6th. From the northern mouth of the Jordan to Wady Fik.

I have given them on the accompanying map, which is the reproduction, reduced by photography (the scale being given in metres), of Macgregor's map, No. VII;^[9] only some slight modifications have been made in the outline according to Schumacher's recent traces (The Jaulân, loc. cit.). The study of this document will show, I think, that depths of 250 metres could scarcely have escaped my investigations. Certainly these soundings have not the positive value which they would have had if they had been made by a professional man, and I have not marked scientifically the precise point of every line, but I operated as carefully as possible, with the aid of a compass and chronometer. It will be observed also that nearly always my figures agree with those which are given, after Molyneux and Van de Velde, on Macgregor's map, and which are indicated in upright figures on the accompanying map. Besides my results positively confirm the statements of the fishermen, who, in response to all my questions, did not cease to assert that the maximum depth of the lake did not exceed 40 metres, and that it was necessary to seek for it towards the middle of the lake between Tiberias and Wady Semakh. Before publishing these facts I made a point of submitting them to Messrs. Armstrong and Lortet, asking the first to let me know from what source he drew his information, and begging the second to re-examine thoroughly the notes of his travels. With the best grace Mr. Armstrong

had the kindness to accede to my request, and this is what he wrote me finally: "I am much obliged to you for having drawn my attention to the depths of the Lake of Tiberias, as they figure, p. 363, in 'Rob Roy on the Jordan.' The map I consulted appeared to indicate the soundings in fathoms instead of giving them in feet, as in Map VII of the 'Rob Roy,' p. 338. Hence the error: the multiplication of 156 by 6, in order to turn fathoms into feet, gave me in fact 936 feet. I have informed the editors of it, so that it shall disappear from the next edition."

From this quarter the question is completely cleared up. There remains M. Lortet's observation on the exact value of which it is impossible to pronounce. "In spite of the fourteen years which have elapsed," writes the learned professor, "I remember very well that this cast of the lead, which astonished me so much, must have been made quite close to the place which I denote by the letter L on your sketch.^[10] Unfortunately I did not verify it; the waves being enormous and the wind very high we were obliged to take refuge in Wady Semakh. But, I repeat, a single observation, made under such conditions, cannot contradict your measurements, which are so numerous and so precise."

Evidently it is quite possible that there may be a kind of very limited abyss at the point indicated by M. Lortet; quite recently M. Delebecque, the engineer, who occupies himself so actively with the hydrographic study of our French lakes, has described an abyss of this kind in the Lake of Annecey;^[11] this well, called the Boubiôz, sinks abruptly more than 80 metres in the subsoil of the lake, while the neighbouring depths scarcely exceed 20 to 30 metres. I think, however, that more precise observations would be necessary to confirm the existence of a similar peculiarity in Tiberias.

In a general way, we may affirm that the Lake of Tiberias is not a deep lake, and that the depth of the water scarcely exceeds 40 to 45 metres, according to the season, the monthly variations being considerable enough, in consequence of the very active evaporation in this over-heated basin. The greatest depths are found in the axis of the Jordan and almost towards the meridian of the lake; the eastern side is steeper, the land being less extended there than on the other shore, and one reaches quickly enough depths of 25 to 30 metres.

The study of the temperatures of the lake comes to the support of what the soundings demonstrated to me. There will be found below the results of a series of thermometrical observations made by means of a Negretti and Zarabra thermometer, the frame of which was constructed by Dumaige, following the pattern adopted by Mr. Milne-Edwards on the "Travailleur" and on the "Talisman," and by H. H. the Prince of Monaco on the "Hirondelle."

I have also condensed in the form of a synoptic table the summary of my observations on the temperatures of the lake:—

——	29th April.	30th April.		1st May.		2nd May.			3rd May.	4th May.
	10h morning.	8h morning.	9h morning.	8h morning.	9h 45m morning.	8h 45m morning.	2h 30m evening.	9h evening.	8h morning.	7h morning.	8h 30m morning.	10h morning.
	°	°	°	°	°	°	°	°	°	°	°	°
Air in the shade	76.10	73.40	74.84	74.30	76.64	74.75	83.84	69.80	76.10	77.45	82.40	84.65
Surface	70.25	71.15	71.15	73.40	73.40	73.40	79.25	69.35	72.50	74.30	75.65	75.65
16.4 feet	..	..	..	71.15	..	..	71.15	..	..	..	..	..
32.81 "	..	..	..	67.64	..	..	68.18	..	69.44	..	..	..
49.21 "	..	..	..	61.70	62.15	..	..	..	63.05	..	..	..
65.62 "	..	..	..	..	..	..	..	..	59.00	..	..	..
82.02 "	59.00	..	..	..	..	..	..	..	..	..	..	..
98.43 "	..	..	..	..	..	..	..	..	59.00	..	..	..
131.24 feet	..	..	..	..	..	..	..	..	58.10	58.10	..	..

Several interesting facts will be shown by the consideration of this document:—

1st. The great range of the variations of surface temperatures in the same day under the influence of the burning sun of Syria; thus, on May 2nd the temperature on the surface was: 73°·4 at 8.45 in the morning; 79°·25 at 2.30 p.m., and 69°·35 at 9 p.m., a coolness of 6 degrees in six hours and a half, a coolness parallel to that of the air above and caused by the action of a strong breeze from the north-west.^[12]

2nd. The relatively inconsiderable depth of the zone subject to diurnal variations is scarcely 15 metres, not more than in the Lake of Geneva, where the mean temperature of the air above is, however, very much lower.^[13] Thus, at Tiberias the temperature of the water, which is 67°·4 to 69°·44 at 32·8 feet in depth, falls rapidly to the number of 61°·70 to 63°·05 at 49·21 feet in depth.

3rd. The uniform temperature (59°) of the deep beds, between 65 feet and 131·24 feet; it is only in neighbourhoods of this last level that the thermometer shows a slight diminution of 0°·9 to 58°·1.

This last fact requires that we should pause an instant; Forel has demonstrated that if we put on one side the figures of the upper bed of 10 metres in depth, which is influenced by the temperature of the air above, we prove that the water of the deep beds gets heated much more quickly in the shallow lakes.^[14] Now, if we compare our results with those obtained by the learned Swiss professor, we shall see that the number of 58°·1 for a level of 131·24 feet is much higher than the average number observed in the Swiss lakes, a number which oscillated during the summer of 1880, for instance, between 41°·36 and 46°·4. This last temperature was taken in the Lake of Morat, the one which, as regards depth, most resembles the Lake of Tiberias. The adjoining table will make these facts clearer:—

		Tiberias = 137 feet.[15] May.		Morat = 157 feet. August.		Zurich = 469 feet. August.
o		o		o		o
—		73·04	Fah.	66·38	Fah.	67·46	Fah.
16·4	feet	71·15		65·84		—
32·81	⁠"	68·54		64·40		66·20
49·21	⁠"	62·24		51·44		—
62·62	⁠"	59·00		49·28		45·68
82·02	⁠"	59·00		48·02		—
98·43	⁠"	59·00		47·30		42·80
131·24	⁠"	58·10		46·40		41·36

 

Lastly, a final table will enable us to compare the figures for a surface temperature nearly equal in two places.

—		Tiberias = 137 feet. May.		Leman = 1,095 feet. August.
o		o		o
—		7·34	Fah.	71·60	Fah.
32·81	feet	68·54		64·40
65·62	⁠"	59·00		54·86
98·43	⁠"	59·00		50·90
131·24	⁠"	58·10		45·68

It is evident—what we have said of the Lake of Morat is enough to show it—that the difference in depth between the two basins is not sufficient to explain the divergence of nearly 7 degrees, which we ascertained between the temperature of the waters of the Lake of Tiberias and that of the waters of Lake Leman at a level of 40 metres.

A certain number of factors come into play to promote this divergence:—

1st The latitude, which is much further south at Tiberias, which causes its average temperature to be much higher than that of Geneva for example.

2nd. The altitude: Lake Leman is at + 1,230 feet, the Lake of Gennesaret at—682 feet; we know the stifling heat which prevails in the deep valley of the Ghôr, not only at Tiberias, but even more perhaps at Huleh, the altitude of which is, however, greater. M. Deshays, chief of the cultivation of the Jewish colony of Jessod-Hamaila, recently installed on the eastern shore of the Lake of Huleh, has assured me that in summer the thermometer frequently rises above 50 degrees, and that several times he had noted temperatures of 55 degrees. Also the water of the Jordan, after having been much heated in this superficial reservoir (5 to 6 metres in depth at the most) arrives in the Lake of Tiberias with a much higher temperature than that of the Rhone at its entrance into the Leman.^[16]

3rd. The continuous flow into the Lake of Tiberias of a series of thermal springs, the principal of which are—

Hammâm d'Emmaus at 143° Fah. (Anderson);
'Ain-Tâbghah at 89° Fah. (Lortet);
'Ain-et-Tineh at 77º Fah. (Barrois).

Others must certainly have their source in the lake itself: it is thus that about 2 or 3 kilometres oft' 'Ain-Tâbghah, on the imaginary line which joins this latter locality to Tiberias, the captain of my boat, an old fisherman, who for 30 years has traversed the lake in every direction and in all weathers, showed me a place where iii winter fish abound because the waters are warmer there than anywhere else; this is evidently the point of emergence of a sub-lacustrine tributary stream.

On the whole these thermometrical observations, incomplete as they are, tend to confirm what the soundings had already demonstrated, to show that the general features of the Lake of Tiberias are those of a shallow lake, the maximum low-water mark of which scarcely exceeds 40 to 50 metres. If there exists opposite the Wady Semakh—at the point indicated by Lortet—an abyss 250 metres in depth, it can only be a narrow shaft with precipitous walls. The question, I repeat, is now clearly stated, and cannot fail to be soon settled.

 

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1. Molyneux, Expedition to the Jordan and the Dead Sea ("Journal of the Royal Geographical Society of London"), vol. xviii, Part II, p. 104-130, 1848.
2. It is thus that the Arabs designate the deep fissure at the bottom of which flows the Jordan.
3. Lortet has made numerous dredgings in the Lake of Tiberias, but no methodical soundings, properly speaking.
4.  Lynch, "Official Report of the United States Expedition to Explore the Dead Sea and the River Jordan," p. 15, Baltimore, 1852.
   See also by the same author: "Narrative of the United Slates Expedition to the River Jordan and the Dead Sea," p. 165, London, 1849.
5. Van de Velde, "Memoir to accompany the Map of the Holy Land," constructed by C. W. M. Van de Velde, p. 39, Gotha, 1858.
6. Macgregor, "The Rob Roy on the Jordan," 7th edition, p. 287, London, 1886. I have not seen the first edition of this book; the only one I have had in my hands is the seventh, dated 1886: it is to this one that the numbers of pages refer, which I will indicate in the course of this article.
7. T. Lortet, "Poissons et reptiles du lac de Tibériade" (Archives of the Natural History Museum of Lyons), t. iii, 1883. A preliminary note had already appeared in 1881 in the Report of the Academy of Sciences of Paris.
8. Macgregor, loc. cit., p. 363. See also the note at the bottom of the page.
9. I have also given Molyneux's soundings as they figure on Macgregor's map; but I think it is as well to remark that these soundings must have been indicated by the English author in a rather arbitrary fashion, for the configuration of the lake on Van dc Velde's map (which contains the first so-called soundings) differs considerably from that on Macgregor's map, especially in the southern portion of the basin. Nevertheless, as I remark further on, Molyneux's figures, even on Macgregor's map, agree nearly always with mine.
10. See map on p. 215.
11. Delebecque, "Atlas des lacs français ": Lake of Annecey. drawn in 1890.
12. During the first four days of my stay at Tiberias, that is to say, the 29th and 30th of April and the 1st and 2nd of May, this fresh breeze rose regularly between 3 and 4 o'clock in the afternoon.
13. All the following figures are given after correction.
14. Forel, "Les Faunes profondes des Lacs suisses," p. 23.
15. Approximate mean depth, see p. 216.
16. According to Forel (loc. cit., p. 30, in the note), the waters of the Rhone have in summer a temperature which varies from 6 to 11 degrees, while the upper bed of the lake is between 15 and 25 degrees.