The study of volcanic inner density distributions using cosmic muons is an innovative method, which is still in a stage of development. This technique can be used to determine the average density along the muon track, as well as the density distribution within a given volume, by measuring the attenuation of the cosmic muon flux going through it. The aim is to study the volcano domes and magmatic conduit systems within a given time-interval. Our first application will be the Popocatepetl, a large active andesitic stratovolcano built in the Trans-Mexican volcanic arc. Its recent activity includes emplacement of a lava dome, with explosions and frequent scoria and ash emissions. This study is part of a longer-term project of volcanic hazard monitoring that includes other Mexican volcanoes, like the Colima. Muon detector design depends on the volume-of-interest dimensions, as well as on the image-taking frequency required to detect dynamic density variations. Our muon-tracker proposal includes 3 planes, each having 16 independent position-sensitive modules consisting on rectangular aluminum tubes ($10x20x320cm^{3}$) filed with a liquid scintillator. The light collection inside each module is carried out using a wave-length-shifting (WLS) fiber matrix, running along the aluminum-tube length, which is bundled together at the tube extremes. The luminous signal readout is carried out using one SiPM optically coupled to the WLS bundle at each modules end. The main detector characteristics, such as time resolution, surface uniformity, and signal amplitude reconstruction using the time-over-threshold technique, will be presented.
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