Background Information and the significance of monitoring:
The existence of the archipelago and overall the diversity of flora and fauna are a result of plate movement and volcano development. The unique attributes of the Galapagos archipelago all stem from the Galapagos hot spot (GHS). A hotspot is when volcanoes occur in the middle of a tectonic plates which is unusual. Usually, 90% of the world's volcanic activity occurs at plate boundaries. Hot spots are an uncommon thermal anomaly from the deep mantle which has resulted in a permanent flow of magma to the surface of the earth during the past 26 million years. This has contributed to the Archipelago being one of the most active volcanic regions on earth. Since 1800 there have been more than 60 eruptions. The Galapagos archipelago consists of two distinct unique kinds of volcanoes: the inverted soup bowl type with deep calderas, and the shield volcanoes with gentle slopes. Considering the level of activity of the volcanoes on the Galapagos, and how other aspects of the islands are affected by such activity, it is important to monitor volcanic unrest and seismicity. For instance, numerous species have adopted areas around volcanoes as their favored habitat, such as species that are already being monitored for population decline. Such monitoring would also allow informed decisions to be made about the position of possible development.
Baseline:
Once the monitoring system is implemented, that will be considered the starting baseline. The data collected thereafter will then compared to historical data collected about volcanic unrest and seismicity, while also referencing data about Hawaiian volcanoes which are similar to those in the Galapagos.
Measurement:
Put simply, a wireless network of remote sensors that will measure data such as seismicity and infrasonic waves will relay data back to a central analysis unit and compared to the acceptable baseline.
The wireless sensor networks will consist of tiny, low-power devices equipped with a radio, various sensors, and a small amount of computational power. A typical sensor is powered by 2 AA batteries and includes an 8-bit microcontroller, 4 KB of memory, a low-power radio with a range of approximately 100 meters and a bitrate of about 38 kilobit/sec. The low cost, size, and energy requirements of sensor networks make these sensors optimal for the measurements we strive for. The sensors would be waterproofed in a sealed container.
There will be one seismometer per island at the central monitoring node which will measure seismicity by detecting the slight movements and vibrations of the earth's surface by converting the motion of the ground and of the seismic waves traveling throughout the earth into digital signals. The exception will be for Isabela island which will have more seismometers since it has six major volcanoes, the majority which are active. Over a time period the amplitude of these signals will be graphed and monitored back at the. The most important aspects are the size, location, frequency of seismic events, the spatial pattern of seismicity, the presence of seismic gaps, and their relationship to known faults and active volcanoes. A minimum of three monitoring sites is required to determine such parameters to an effective and accurate degree. The seismometer should record ground acceleration with a dynamic range of 10-5 to 1 g (acceleration due to gravity) in the frequency band 0.1 to 20.0 Hz, to a precision of 5 ms.
The purpose of the infrasonic microphone is to collect data unavailable from the seismometer. Infrasound waves, which are low-frequency acoustic waves in the range of 1-20 Hz. Unlike seismic waves propagating in the earth, infrasonic airwaves offer a relatively unfiltered representation of source motions. Time-varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances (65 km from the vent). Acoustic pressure traces in the near-infrasound bandwidth (0.1^20 Hz) are valuable because they reveal information about physical motions at the vent. Using multiple infrasonic sensors distributed over an area can be used to cancel noise (from things such as wind) as well as triangulate the source of an eruption event.
The sensor network will include devices combining infrasonic microphone (a Panasonic BM-034Y), in which the filtering circuitry and amplification has been custom modified, and a wireless sensor node. Three such devices could send sampled data at approximately 102 Hz, transmitting radio messages with multiple samples about 4 times a second to a nearby receiver. The receiver relays this data to a modem, which provides a long-distance serial radio link, back to a matching modem at the observatory, 9 km away, using a pair of directional antennas. The modem at the observatory is connected to a computing center, which records and visualizes signals from the sensor network.
It is also essential to determine a common time base across the wireless sensor nodes. This can be done using wireless GPS receiver. The GPS wireless node receives a time pulse every second from the GPS receiver and relays the pulse to the microphone equipped sensors via radio. Each senor marks the infrasound sample taken when each GPS time pulse is received, allowing the signals from each mote to be synchronized across time.
There are two other kinds of sensors than the sensors equipped with the microphones. In a network, three-fifths of the sensors should have the infrasonic microphones. One-fifth of the sensors should be receivers that forward data over a long-ranges back to the central analysis station, and another one-fifth should provide the time base.
Combining the data culled from the seismometer and microphone will provide a more complete picture of the situation throughout the archipelago. The frequency of measurement should be continuous since several islands contain active volcanoes. Analysis of data consists of comparing infrasonic waves and the seismic data respectively over a time period.
Implementation:
The wireless sensors will be placed on the flanks of the volcanoes. Seismometers will be located at the central monitoring nodes on every island. Continuous measurement should be taken. If an active volcano is identified, geophysical and geochemical baseline monitoring data should be gathered. Further monitoring sites should be established and distributed over the entire volcanic system, including active vents, crater lakes, and areas of ground cracking.
Citations:
Galapagos Geology on the web. Retrieved November 12, 2004 from http://www.geo.cornell.edu/geology/Galapagos.html
Harpp, Karen & Geist, Dennis (1998). Galapagos Plumology. Noticias de Galapagos. Retrieved November 14, 2004, from http://www.darwinfoundation.org/articles/n5900049815.html
International Union of Geological Sciences. Geoindicators. Retrieved November 15, 2004 from http://www.lgt.lt/geoin/
Johnson, J.B., Generation and Propagation of Infrasonic Airwaves from Volcanic Explosions, Journal of Volcanological and Geothermal Research, 121, 1-14, 2003.
Welsh, Matt (2004). Monitoring Volcanic Eruptions with a Wireless Sensor Network. Retrieved November 12, 2004, from http://www.eecs.harvard.edu/~mdw/proj/volcano/
