Density Measurement of Mt. Asama and Showa-Shinzan dome

A starting point for the method of applying muon radiography in volcanoes was carried out by Tanaka et al. (2007a, 2009) in Mt. Asama and is one of the best references in the vulcanology field on the subject. The picture abobe is from a similar study that was carried out in the same year by almost the same team in the Showa-Shinzan volcanic dome that was formed in 1944 in Mt. Usu and shows an average density profile of the dome obtained with the muon radiography method used. The picture serves to represent what can be obtained in both studies.

Initially, the study consisted of a radiographic probe using muons at Mount Asama, Japan, and sought to show whether it was possible to explore the internal structure of the heterogeneous crust surface, as in the case of a volcanic dome.

Mount Asama is one of the most active andesitic volcanoes in Japan and had erupted on September 1, 2004. Its altitude is about 2560 m and has a crater with a diameter of approximately 350 m. With such a prominent topography and with one of the drawbacks of this technique being the need of the observation to be made above the level of the telescope, the volcano is a good case for such an application.

The detectors of the muon telescope used consisted of emulsion cloud chambers (ECC) made of iron plates and nuclear emulsion films.

In the two most important results of this study was the evidence of the 2003 crater that was covered by a layer of dense lava that deposited during the eruption in 2004 and which now functions as a ventilation cap and also the discovery of a porous and permeable region below the cap.

The importance of this work paved the way for relatively simple and inexpensive muography methods, showing that it could be applied to any type of geological structure above the detector and that allowed to obtain information on the distribution of densities of the various materials.

Publications:

"High resolution imaging in the inhomogeneous crust with cosmic-ray muon radiography: The density structure below the volcanic crater floor of Mt. Asama, Japan" (Tanaka et al., 2007a)

"Imaging the conduit size of the dome with cosmic-ray muons: The structure beneath Showa-Shinzan Lava Dome, Japan" (Tanaka et al., 2007b)

"Detecting a mass change inside a volcano by cosmic-ray muon radiography (muography): First results from measurements at Asama Volcano, Japan" (Tanaka et al., 2009)