IS13, Easter Island, Chile

Easter Island was allegedly called “Te pito o te henua” or “Navel of the World” by its original Neolithic inhabitants. The island received its current name—Isla de Pascua or “Easter Island” — because it was discovered on Easter Sunday of 1722 by its first recorded European visitor, the Dutch explorer Jacob Roggeveen. The mysterious giant stone monoliths, known as Moai, which stand along the coastline gazing inwards, are recognized the world over as representing an ancient civilization at its cultural zenith. However, this vision contrasts sharply with other Moai lying in ruin among the volcanic rocks from which they were erected and symbolizing the fall from grace of an indulgent society unable to live in harmony with nature. Although now nearly treeless, core samples from the crater lakes on Easter Island reveal that lush forests of a now extinct palm once thrived here. Some archaeologists and historians assert that the indigenous Easter Islanders used the palm wood to construct houses, build fishing canoes, fuel fires and finally to serve as rollers to transport their massive statues built in the island quarries. As the island’s inhabitants decimated the once abundant forests and competition for remaining resources intensified, the islanders fell into violent conflict from which their culture never recovered.

One of the world's most isolated inhabited islands, Easter Island—a volcanic high island, consisting of three extinct volcanoes—is located some 3,600 km west of Chile in the vastness of the South Pacific Ocean. That coastline of the triangular-shaped island is rugged with only a few sandy beaches, while the interior comprises gently rolling hills, volcanic in origin. Weather wise, Easter Island has a sub-tropical oceanic climate. Hence, extremes of temperature are rare and the yearly mean temperature is 22°C.

Infrasound station IS13 is located in a wooded area in the interior of Easter Island. The survey for this completely new station — the 26th to be certified out of a total of 60 planned stations that will make up the International Monitoring System's (IMS) infrasound network — was carried out in May and June 2000. The Department of Geophysics of the University of Chile conducted the survey in collaboration with the CTBTO's Provisional Technical Secretariat (PTS). The island is one of few locations in the world to host three IMS stations: in addition to IS13, Easter Island also hosts auxiliary seismic station AS18 and radionuclide station RN19. This particular trilogy of IMS verification technologies is also found on Tahiti.

The construction of IS13, undertaken by the Chilean Commission for Nuclear Energy (CCHEN) in cooperation with the PTS, was completed in only eleven months, between January and November 2004. A team of CCHEN engineers and technicians continue to carry out the station operation and maintenance. Because wind is a marked feature of the island’s climate, each array element has been set up in a forested area to reduce the influence of wind-generated noise. Another feature of IS13, common to all IMS infrasound stations, is a weather station installed at the central array element that samples temperature, wind speed, wind direction and barometric pressure data. The sampling rate is one sample per second for IS13.

Authenticated infrasonic data from each array element, along with meteorological data, is sent in twenty-second data frames through the Global Communication Infrastructure (GCI) to the International Data Centre (IDC). IS13 is not the only IMS station on Chile’s Easter Island. Radionuclide station RN19 and Auxiliary Seismic station AS18, located just two km away from the IS13 array elements, also scan the earth for evidence of nuclear explosions. The island’s exposure to wind makes it an ideal location for radionuclide measurements, as airborne radioactive particles can travel with the wind from afar.

Easter Island’s infrasound station is unmanned. However, a caretaker is present on the island to provide first remedial actions in case of failure of any station components. Each array element is powered by an independent solar power supply with a back-up capacity of about ten days. Consistent with the CTBTO’s certification process, IS13 on Easter Island successfully met all minimum requirements for an IMS infrasound station. As of November 2004, IS13 officially began transmitting data to Vienna. All authentication devices and GCI infrastructure were in place and working properly. Throughout the 90-day test period, data availability amounted to a total of 99.9%. IMS staff members anticipate that performance will be enhanced at IS13 when trees and bushes within the array elements reach a sufficient height and density, further reducing background noise.  IS13 was certified on 15 July 2005. In addition to the above-mentioned three IMS stations, Chile also hosts another auxiliary seismic, one more infrasound station, a hydroacoustic station and two radionuclide stations. Learn more about Chile and the CTBT.