Hot springs, geysers, mud pots, and fumaroles are dynamic surface features that represent interacting subterranean systems of water, heat, and rocks. Identifying the locations of these features and monitoring their heat, water flow, and chemistry can provide land managers with data needed to make informed decisions about management options.

This chapter describes vital signs and contains options for monitoring surface and near-surface geothermal features, such as hot springs, geysers, mud pots, and fumaroles. Its focus is the description of techniques for detecting change in hydrothermal systems through time due to natural or human-related causes.

The goal of this chapter is to describe selected techniques for monitoring important vital signs of geothermal systems. Information in this chapter will not make the reader an expert in all geological aspects of geothermal systems. Some monitoring techniques are simple and can be performed by interested volunteers with no specialized background. Other techniques are complex and are best done by experts, with study results interpreted by seasoned practitioners. The described monitoring options may not meet all statutory and regulatory requirements that land managers may face.

The terms geothermal and hydrothermal have specific connotations as used in this chapter (Jackson, 1997). Geothermal refers to any system that transfers heat from within the Earth to its surface. Hot rocks, without water, are geothermal. Hydrothermal is a subset of geothermal, and means that the transfer of heat involves water, either in liquid or vapor state (hence the “hydro”). Hot springs and geysers, for example, are hydrothermal