286 
As regards the thickness of the lahar, for the present there are only 
few data at our disposal. In the upper course in the neighbourhood 
of the lahar Gupit the thickness is according to my estimate more 
than 50 m., but here the breadth is only about 200 m. This great 
thickness is connected with an accumulation behind the Durga-canyon 
(with a breadth of only 10—15 m.), through which the whole lahar 
of 1919 had to pass. This upper part of the lahar has now been 
strongly attacked by erosion, so that its thickness can be measured. 
More important for an estimate of the cubical capacity of the lahar 
is the thickness within the plain. Kemmerrine (lit. 14 p. 810) mentions 
in the town of Blitar a local thickness of 1,55— 2,20 m. and observes 
that in the plain inundated by the mud flow all vegetation is covered 
under a layer of sand and stones to a depth of 40—60 cm. 
If we assume an average thickness of the mudflow of 50 cm., 
the cubical capacity of the lahar of 1919 would amount to 0,5 200 
million eubie m.—=100 million cu.m.; if we assume the average thick- 
ness to be20 em. only — and to assume a still lower average thickness 
would be quite absurd — then the cubical capacity would amount 
to 0,2 > 200 million cu.m. = 40 million cu.m. The material of the 
lahar consists partly of ash, lapilli and bombs from the eruption of 
1919 and in part of old lahar-material, brought up, eroded and 
swept away by the new mud flow. The cubical capacity of the 
crater lake amounts to 38 million cubic metres (lit. 14) *). 
The proportion of solid materials (A) to water (W) in the hot 
lahar of 1919 consequently would have been as follows: 
Supposing an average thickness of the lahar of 50 em. 
A 100 
Supposing an average thickness of the lahar of 20 cm. 
eae 
|| Aere) nage 
Now let us take up again the Katmai region. 
It appears that Griaas has quite overlooked in his speculations that 
before the eruption of 1912 the Katmai voleano must have possessed 
a crater lake, just as is now the case according to his section 
1) After the eruption of 1901 the water-mark of the crater lake was lowered 
artificially so that the cubical capacity was reduced from 44 million cu.m, (lit. 
10) to 38 million cu.m. At present there is a tunnel under construction with 
a view to have the crater lake dry before the next eruption and in future to 
avoid the formation of hot lahars. 
