A progress report on the bathymetric survey of Windereme undertaken in June 1937 by the Hydrographic Department of the Admiralty. The brief article outlines the background of the surveying process as well as the initial effectiveness of the survey work. There is a brief background to the geomorphological processes which were involved in shaping the Lake District topography, as well as some explanation of previous studies undertaken in the area. The report includes a figure showing the cross sections of lake beds and a figure detailing a core from the bottom deposits of Windermere

Mortimer, C.H.

Worthington, E.B.

English

Aquatic Commons

II. ARTICLES ON RESEARCH. 
The following are progress reports on research which is not yet 
complete. In due course the results will be submitted for publication 
in suitable journals, but meanwhile these articles are not intended to 
be referred to as scientific papers. 
BATHYMETRIC SURVEYS AND LAKE DEPOSITS. 
by C. H. Mortimer and E. B. Worthington. 
A bathymetric survey of Windermere by the echo-sounding 
method was undertaken for the Association in June 1937 by the Hydro-
graphic Department of the Admiralty, and we are deeply indebted to 
the Hydrographer, not only for the detailed charts, but also for opening 
up new problems of research which have already given results of strik-
ing interest, and promise more for the future. 
Lt.-Commander W. J.Farquharson, who had already had extensive 
experience of survey in connection with biological research on the 
John Murray expedition to the Indian Ocean, together with a Petty 
Officer, spent five weeks at Wray Castle on the field work, and some 
time afterwards at their headquarters, plotting results and drawing 
charts. The survey was undertaken in the first place to provide more 
34 
detailed knowledge of depth than was available in the original survey by 
H. R. Mill, published in 1895, because the need was felt for real 
accuracy in plotting the distribution of flora and fauna. The instru-
ment used, which was fitted to the Association's motor launch, was the 
new magneto-striction echo-sounding recorder, manufactured by 
Messrs. Henry Hughes & Son Ltd. In this instrument a supersonic 
sound impulse is emitted at frequent intervals, and the time taken for 
the echo to return to the surface is recorded on a continuous chart with 
an appropriate depth scale. Its advantage over older methods is 
shown by the fact that it was possible within a few weeks to complete 
nearly 300 cross sections on Windermere, with continuous soundings, 
enabling a depth chart of great detail to be drawn. The results, on the 
scale of 6 inches to the mile, will be printed in due course by the 
Hydrographic Department of the Admiralty, and some additional 
sheets covering part of the lake in still more detail are available on the 
25-inch to mile scale. It is interesting to note that these differ from 
H. R. Mill's original chart only in matters of detail. 
An examination of the first few records obtained revealed at once 
that the instrument showed not only the depth of water but also the 
depth of soft mud deposits overlying the hard floor of the lake, the 
explanation being that some of the sound waves were reflected from the 
soft surface of the mud and others from the hard rock or gravel below 
(see figure 2). When passing over a bare rock bottom a characteristic 
record was obtained in which a series of echoes were registered equi-
distant from each other, as the sound waves were reflected several times 
to and from the surface and bottom. This was not, of course, the first 
time that double echoes of this type had been obtained with the 
machine, but the peculiar conditions of basins in the Lake District seem 
to be, particularly favourable in revealing the depth of soft deposits. 
In order to obtain similar records from other lakes, the instrument 
was adapted to row-boats and with the aid of an outboard motor 
preliminary surveys were made of Wastwater, Ennerdale, Derwent-
water, Bassenthwaite and Esthwaite, with illuminating results. Also, 
to supply the essential proof that the distance between the first and 
second echoes really represents the depth of mud, a boring apparatus 
was devised to extract cores of the deposits. 
The results may have an appeal especially to geologists in suggest-
ing how the recent phases of the Lake District's history can be further 
35 
elucidated, but before proceeding to their discussion it is necessary to 
consider a few of the changes which have brought about present 
conditions. The topography of the district in its broad features and 
sometimes in minute detail finds its explanation in the existence some 
ten or twenty thousand years ago of a sheet of ice, thick enough at the 
time of its maximum extent to fill the valleys with glaciers, and in some 
places to overflow them. At the heads of the valleys or at points of 
confluence of several glaciers the pressure of ice was greatest and hence 
the grinding power of the rock fragments contained in it was enhanced 
to gouge most deeply into the rock. This explains why Windermere, 
in common with many other lakes, is deepest in that part of its basin 
nearest the head. The debris from the grinding process, in the form 
of coarse morainic material or of fine boulder clay, was deposited either 
along the sides of the valleys or at the points where the glaciers melted. 
Thus morainic dams were built and have contributed greatly to the 
formation of lakes. As the glaciers receded other moraines were left 
to form islands or deposits of gravel and boulders on the lake floor, and 
since that time the original condition of the lakes has been altered by the 
addition of weathered rock brought down by water, the larger frag-
ments forming deltas and the smaller being deposited as fine silt on 
the bottom of lakes. The remains of plant and animal life in the lakes 
are continually falling to the bottom with the silt, and these form the 
muds which differ in constitution from one lake to another. 
Studies by Pearsall on the distribution of water plants in the Lake 
District have demonstrated the importance of the amount and type 
of mud as controlling factors. At the outset it was clear that the plant 
population of those lakes which drain the central hills of igneous rock 
of the Borrowdale series, such as Wastwater, Ennerdale and Butter-
mere, differed from that in lakes draining the gentler slopes of the 
stratified Bannisdale slates, etc., on the margin of the district, such as 
Windermere and Esthwaite. The stratified rocks weather more 
readily and produce finer silt, so that the regional distribution of the 
plants finds its explanation in the different silting rates of the two types 
of lake. Thus the original condition of the lake basins is being modified 
in the two types at different rates, and they, with their plant and animal 
populations, represent stages in an evolutionary sequence : in this 
sense Wastwater may be considered to be primitive and Esthwaite to 
be evolved. 
According to this hypothesis, one would expect to find much more 
deposit of mud in an evolved lake than in a primitive one, and this is 
born out forcibly by the echo-sounding records (figure 3). Wast-
water contains very little of the typical soft post-glacial mud ; Winder-
mere and Esthwaite contain much more. 
Up to the present, cores of the bottom deposits have been raised 
only from Windermere, and though somewhat compressed in extraction 
they have been obtained to depths of about 8 feet and show an interest-
ing sequence in the deposits since the ice age (figure 4). Above the 
bottom gravel are glacial clays, made up of fine layers or laminae, 
representing alternate coarser and finer deposits. These clays are 
reminiscent of the varve clays in Scandinavia on which de Geer 
founded his famous Swedish scale of geochronology, and their origin 
is probably likewise due to the annual fluctuations in the amount 
and coarseness of silt carried into still water by glacial rivers. Above 
F I G U R E 3. Cross sections of lake beds of Wastwater, Windermere 
and Esthwaite Water, redrawn from records obtained with the 
echo-sounding machine. 
36 
37 
the lower clay comes a diatomaceous 
layer containing the minute siliceous 
shells of diatoms, many of which grow 
in the lake to - day. Above this the 
laminated glacial clay reappears, and 
above this again the diatomaceous mud is 
found, which appears to be continuous 
with the present surface mud. This 
layering may be tentatively suggested to 
be the result of climatic fluctuations at 
the end of the last ice age. The main 
ice sheet left either a scoured rock basin 
or a deposit of coarse gravel at the 
bottom. During the recession of the 
ice a glacier remained for a considerable 
time in the upper part of the Winder-
mere valley. With the melting ice each 
spring considerable amounts of silt were 
washed into Windermere, and deposited 
in still water producing laminated clays. 
During a relatively warm period diatoms 
flourished in the lake, and their shells 
are found in the diatomaceous deposits. 
The upper laminated clay marks the 
return of a colder climate, and of a 
glacier in the upper part of the valley. 
Since these cores from Windermere were obtained, they have been 
examined by several scientists. Dr. H. Godwin of Cambridge has 
made a preliminary examination for pollen and found that the pollen 
content though not high is probably adequate to show beyond doubt 
the interglacial or post-glacial status of the different horizons. Mr. 
L . R. Wager of Reading University confirmed that the inorganic 
particles in the laminated clays are of the size and shape that would be 
expected to be deposited from glacial streams. Professor T . M. 
Harris of Reading University and Mr. R. Ross of the Natural History 
Museum are examining the diatom shells; and Dr. G. H. Mitchell of 
the Geological Survey has helped materially in pointing out the 
significance of this evidence in relation to other post-glacial deposits. 
A thorough examination of deposits from Windermere and other 
38 
lakes would probably affect not only knowledge of quaternary 
geology of the Lake District but also botanical, archaeological and 
climatic studies. For example, it might be possible to relate a detailed 
study of the varves with analyses of the pollen so as to date accurately 
the history of forest development in the area. This would involve 
intricate and specialised study beyond the scope and time of the 
Association's staff, so it must wait until some special facility for re-
search becomes available. 


Bathymetric surveys and lake deposits

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Bathymetric surveys and lake deposits

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