98
sortie du lac sur les restes du dépôt même de cette lave, dont les
derniers jets moins-liquides se seront refroidis en formant les
deux murs qui s’élèvent au-dessus des eaux. Le résultat de cette
coulée aura été un trou-dans lequel toutes les sources d’alentour
ont accumulé leurs eaux, & l’auront rempli jusqu’à la hauteur
du point où la lave forme les deux extrémités en pente de la
double coulée; car l’eau qui sort du lac n’est & ne peut être que
le trop plein de son lit. / The lake Pavin produces a complete
illusion at fi rst sight (see board 44 [Fig. 5.4 ]) ; its circular shape,
its high edges formed by lavas and shaped as a funnel absolutely
provide the idea of an old crater; but the opening by which the
small Couze River escapes towards the north, and hillslopes by
which both ends of its circular volcanic mass close on each side
of the opening do not show the mark of some failure created by
the lava, because the course of the river at the exit of this lake is
not blocked by any remnant of lava fl ow. Moreover the diameter
of the walls of the lake Pavin would not correspond to their
absolute rise above ground level. If one wants to explain the
formation of these walls, one needs to admit, as the inspection of
the site seems to prove it, that a current of lava came out the
volcanic hill of Monchal, much higher that the lavas of the lake,
and was divided into two circular branches which ended in the
place where the small river escapes: an effect so singular in the
behaviour of a molten lava that it comes as a surprise, but with-out any doubt, an obstacle, nowadays invisible, made the lava
fl ow to be divided this way. As for the depth of the lake itself, and
we do not take the height of walls into account, we can explain it
by saying that the lava fl ow which formed it settled on a ground
which still makes the bottom of the lake, whose depth is, how-
ever, 120 feet; lavas would have spread all around by heighten-
ing the ground to a suffi ciently great distance. The small river
runs at the exit of the lake on the remaining deposit of this lava,
whose last, less liquid streams would have cooled by forming the
two walls which rise above water. The result of this lava fl ow
would have been a hole in which all the surrounding sources
accumulated their water, and would have fi lled it until the eleva-
tion of the point where the lava forms the two steep ends of the
double lava fl ow; because the water which leaves the lake is and
can only be the overfl ow above its bed. [...]” (Huot 1828 , p.688).Shortly after, Dufresnoy , the defender of the “craters of
elevation”, mentioned both lakes Pavin and Laach-See, then
said to be “ well known ”, as having the same origin, but did
not choose between the two explanations, i.e explosion or
collapse. What interested him is that Pavin did not belong to
his ‘uplifted crater’ category:Fig. 5.4 Extract of engraving
board 44 of N. Desmarest
( 1827 ) used by J.-J.E. Huot
( 1828 ) to propose a new
explanation. Compared to the
version as of 1823, Fig. 5.2 ,
currents of lava that come out
the lake Pavin were added as
well as arrows that indicate
the direction of lava fl ows
emitted by the puy of
Montchal
P. Boivin and S. Jouhannel