ABSTRACT
This chapter describes the various methods by which the changing positions of large numbers of stations can be monitored by standard surveying methods. Once the network of fixed stations has been measured, the detection of displacements due to ground deformation will depend upon a later re-measurement of the same stations. The best site for a tilt station or tiltmeter under this kind of deformation regime would therefore be near the point of maximum inclination on the flanks, whereas a network measuring horizontal deformation would be best placed across the summit. Despite the maximum vertical deformation at the summit, tilt is zero here, and reaches maximum values on the flanks. The best way to achieve this information rapidly is with a trilateration network that also includes trigonometric levelling. For levelling traverses on active volcanoes, a self-levelling instrument is virtually essential because of the necessity for speed, and will correct small changes in horizontality of the instrument.
