In this chapter, we describe basic features and give some current applications of the most popular detection technology used in muography: the scintillator-based muon detectors, widely used not only in volcanology, where their properties find natural applications, but also in geosciences, archeology, non-invasive industrial control, civil engineering, homeland security, nuclear non-proliferation and more. As we will emphasize in the following sections, there are many advantages in the use of scintillators, which are known to be robust -and therefore usable in harsh environmental conditions -and offer real-time analogic measurement capabilities with a good space and time resolution. The design of such detectors is flexible and may be used in many different ways depending on the target under study, the field conditions, the modularity of the detectors etc. Throughout this chapter, we will focus on one particular muon detector (also referred to as "muon telescope") originally designed to study the active volcanic dome of the Soufrière of Guadeloupe to show the generic features of this detection technique.

In order to identify the dominant non‐Newtonian effects which occur during the injection of a new Newtonian magma through a partially crystallized magma chamber, we have performed some preliminary analogue experiments which enable us to point out several features induced by the non‐Newtonian properties of the host fluid during injection processes. These experiments were performed in a three‐dimensional device and involve complex non‐Newtonian fluids—clay suspensions in which rheological properties such as bulk strength, yield strength and rheofluidification exponent may vary. Forced injection takes place through a slot which in the case of a Newtonian host fluid is the geometry that provides planar structures. Depending both on the density contrast and on the rheological contrast between the injected dyed water and the host fluid three kind of structures were observed: (1) permanent plumes when the injected water is lighter than the suspension exhibiting rheological properties close to Newtonian fluids; (2) pseudo‐fountains and spreading at the bottom of the tank with a destabilizing density contrast and in high yield strength/more viscous suspensions; (3) fountains with a slightly stablizing density contrast. The implications for magma chamber evolution are briefly discussed. In particular it seems that homogeneous non‐Newtonian media inhibit the formation of planar structures and partially crystallized magma may induce the spreading of the new magma at the bottom or at the top of the chamber regardless of the density contrast between the magmas.

Muography uses muons contained in the natural cosmic rays to determine the density of rock volumes. The measurements consist in counting the muons emerging from the target to determine the screening effect produced by the rock. Because the larger the rock thickness, the smaller the number of muons able to cross, the time resolution that can be achieved by muography to monitor density changes is on the order of one or two weeks for kilometer-sized volcanoes. This limitation of the method can be reduced by joining muography with high time-resolution measurements like passive seismic monitoring. In the case of structural imaging, muography benefits from the fact that muon trajectories are linear, making the tomography problem simpler than for other geophysical techniques like electrical resistivity tomography. Experiments performed on La Soufrière of Guadeloupe volcano are described to show how muography can be used to contribute to structural imaging of an highly heterogeneous lava dome and to detect abrupt transient hydrothermal phenomena likely to produce dangerous explosive events.