125eruptive dynamics dominated by surges deposits controlled
by the topography, even if significant variations may be due
to later erosional processes. To avoid at the maximum the
effect of post-eruptive erosional processes, some anomalous
points with very low thickness values were not taken into
account.
Most important thickness variations result in isopachs
undulations (see isopachs 0.5 m and 1 m east to the Pavin,
and between the Montchal and Montcineyre cones). Such
geometry cannot only result from a unique dynamism such
as wind-controlled ash fall deposits. Thus, it is likely that this
phenomenon expresses when some particular volcanic dyna-
mism such as base surges flow on an irregular topography at
intermediate distances from the vent. The bulk of sedimen-
tary structures, such as cross-stratification, are also mostly
found in this zone which is consistent with this observation.
On the Fig. 6.16, dashed isopach curves indicate that the
drawing is not based on measured thicknesses but that it is
either an interpretation from this study (to the west) or based
on other observations: to the south and east, dashed isopach
curves are based on Bourdier ( 1980 ), and to the north it is
based on observations from Lavina who found rare outcrops
of preserved fine trachytic particles attributed to the Pavin
(Thonat et al. 2015 ).Fig. 6.16 Isopach model of
the Pavin deposit (thickness
and grid in meters,
RGF93 – Lambert93)
6 Characterization of Phreatomagmatic Deposits from the Eruption of the Pavin Maar (France)