Structure and CO2 budget of Merapi volcano during inter-eruptive periods

Abstract Soil temperature and gas (CO2 concentration and
flux) have been investigated at Merapi volcano (Indonesia)
during two inter-eruptive periods (2002 and 2007). Precise
imaging of the summit crater and the spatial pattern of
diffuse degassing along a gas traverse on the southern slope
are interpreted in terms of summit structure and major
caldera organization. The summit area is characterized by
decreasing CO2 concentrations with distance from the 1932
crater rim, down to atmospheric levels at the base of the
terminal cone. Similar patterns are measured on any
transect down the slopes of the cone. The spatial distribution
of soil gas anomalies suggests that soil degassing is
controlled by structures identified as concentric historical
caldera rims (1932, 1872, and 1768), which have undergone
severe hydrothermal self-sealing processes that dramatically
lower the permeability and porosity of soils.
Temperature and CO2 flux measurements in soils near the
dome display heterogeneous distributions which are consistent
with a fracture network identified by previous
geophysical studies. These data support the idea that the
summit is made of isolated and mobile blocks, whose
boundaries are either sealed by depositional processes or

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