In this paper, an intelligent surveillance system using sensor networks for monitoring active volcanoes has been presented. While wireless sensor networks can generically be used for a wide variety of applications, breakthrough innovations are most often achieved when driven by a genuine need or application, with its specific system-level and science-related requirements and objectives. Hence, our work focuses on the development of a specific surveillance system for active volcanoes. We combine sensor network system engineering with systems-on-chip implementation to develop an integrated surveillance system called Sensor Networks for Active Volcanoes (SNAV). We report SNAV specific science-related requirements and system-level operations for this surveillance system. Development of the SNAV node system-on-chip (SoC) is then presented. A rapid SoC prototyping of the control and computing subsystem was implemented as an exploratory device based on reconfigurable SoC platform architecture. A low-power radio was developed as an embedded wireless communication core for SNAV system-on-chip designs. The success of this work enables low-power, low-cost sensor networks for intelligent surveillance system applications.