  Muography is an imaging technique for large and dense structures as volcanoes
or nuclear reactors using atmospheric muons. We applied this technique to the
observation of the Puy de D\^ome, a volcano 2 km wide close to
Clermont-Ferrand, France. The detection is performed with a
1m$\times$1m$\times$1.80m telescope made of 4 layers of single gap glass-RPCs
operated in avalanche mode. The 1 cm$^2$ pad readout uses the Hardroc2 ASICs.
The three data taking campaigns over the last three years showed that a RPC
detector can be operated in-situ with good performances. Further developments
to decrease the gas and power consumption and to improve the position and
timing resolution of the detector are ongoing.
