Monitoring of an active volcano is currently undergoing a revolution with many new methods being introduced to aid in the prediction of eruptive activity. Remote sensing has greatly improved our capability, particularly for more remotely located volcanoes. Different monitoring techniques can be characterised by the frequency that data is obtained. This can vary from between monthly for spring data to 100 samples per second in the case of seismicity. It is important not to forget the most basic form of monitoring which is pure observation. Information such as variation in the size of the volcanic plume, a change of colour, the height of an eruption column, formation of new fumaroles, change in the size of a crater lake etc. can provide critical information for hazard assessment. Historically the main methods could be divided into the following:a) Seismic
At many volcanoes this represents the principal method of 'reading' the behaviour of the volcano. Even with a small network it is often possible to observe seismicity related to the rising magma body prior to an eruption.b) Geodesic
When magma pushes its way up from beneath a volcano there is usually associated movement of the volcanic edifice. This can be recorded by using GPS equipment, EDM (Electronic Distance Measurement), Levelling or Tilt meters. Satellite-based sensors can also be used to identify and expanded edifice (INSAR).c) Geochemical
This area of monitoring looks at the interaction between fluids and gases originating from a volcano and the surface or near sub-surface environment. Also the geochemistry of solid products can provide vital information in the analysis of the state of activity. The following measurements are commonly carried out: the flux of gas released by the volcano; its composition; geochemistry of the discharge in local spring waters; flux of gas diffusing though the ground; characteristics of ash produced by explosions; geochemistry of samples from domes or lava flows. Various satellite-based sensors have been used to detect both the SO2 and ash content of volcanic plumes.Plume gas composition
When the volcano does not have explosive activity it is possible to climb to the crater and take samples directly from the fumaroles. This is the ideal way to analyse the composition of the volcanic gases. Samples are taken in special sampling bottles and are later analysed in the laboratory. Concentrations of the major gas species can be obtained (CO2, SO2, HCl, N, He, Ar, etc.), also isotopic analyses are usually carried out of the water isotopes. It is planned to install diffusion tubes near to the summit as an alternative method for analyzing the major gases.Juan Carlos sampling fumaroles Ash studies
Volcanic ash is a term given to small particles (less than 2 mm in diameter) of rock, minerals and volcanic glass that are expelled from a volcano during an explosive eruption... see more
The other less commonly used techniques can be divided as follows:
Monitoring of Volcán de Colima is carried out by members of the Volcanological Observatory and the Committee for the Evaluation of Risk of the Universidad de Colima. At the Centre of Exchange and Research in Volcanology we are responsible for geochemical, thermal and infrasound monitoring.
Information on seismic and deformation monitoring can be found on the Observatory website along with images from the cameras being installed at various points close to the volcano.
This area of monitoring has proved very useful at Volcán de Colima. There have been some effusive periods that have not given any signal in the seismicity but did produce geochemical anomalies prior to their onset (2001-3).
In this area of monitoring we also include thermal monitoring. This can be carried out using satellite-based sensors which give a low resolution but a guaranteed daily measurement if the skies are free of clouds. CUICA has receivers for data from two types of sensor: AVHRR and GOES. Recently ground-based monitoring has been introduced at Volcán de Colima.