Air Namibia, Flamingo February 2008 (Text and Infrasonics photos by Tim Osborne) Stock photo Mount St Helens Eruption May 18 1980 (US Geological Survey — Austin Post)
The Shot That Was Heard Around The World -Twice
When Mount Saint Helens in northwestern USA blew its top on 18 May 1980, the sound of the explosion was heard by people within a radius of 100 kilometers. Amazingly it was also heard at McMurdo Sound in Antarctica roughly 12,000 kilometers away.
Scientists from the University of Alaska were operating a special listening device to detect very low-frequency sound waves. They were at Antarctica to determine if the aurora australis (southern lights) produced sound as some people had claimed. Instead, the device picked up the very large sound wave from Saint Helens’ volcanic blast. Hours later it picked up another wave from the explosion as the sound circled the globe the long way around for the second time. The direct and long-distance sound waves continued to be detected for days each time they passed the station.
Intelligence agencies have long been aware that large explosions, such as above-ground nuclear tests, emit sound waves that travel in the upper atmosphere and can be detected at long distances by ground listening posts. In an effort to ban all nuclear explosions, the Comprehensive Nuclear Test Ban Treaty (CNTBT) was established in 1996. A total of 121 countries, including Namibia, are members of the treaty. Even though Namibia has the largest open-pit uranium mine in the world, it is committed to the peaceful use of uranium.
The CNTBT Preparatory Commission, based in Vienna Austria, was charged with the duty of verifying adherence of countries to the treaty. The Commission is establishing 321 stations around the world, including two in Namibia, where sophisticated equipment scans for illegal nuclear activity. The stations send continuous data transmissions to the headquarters in Vienna. Four kinds of detection equipment -radionuclide samplers, hydroacoustic sensors, seismic sensors and infrasonic stations -look at different aspects of illegal nuclear testing.
The radionuclide samplers filter various radioactive particles and noble elements from the atmosphere. Nobel gases such as neon, argon, xenon and krypton that are released during underground nuclear explosions are rare in the atmosphere. When high levels of radioactive particles are detected, an alert is activated for the other stations to try and pinpoint the source.
There are 11 hydroacoustic stations that monitor the oceans of the world. They regulate natural events such as sub-sea volcanic activity, earthquakes and man-made disturbances.
Seismic sensors detect activity ranging from earth-quakes to road-building and mine blasts. When nuclear bombs are exploded underground, a seismic shock wave travels through the earth. The sensors are able to pinpoint the exact location and size of the explosion. Namibia’s Geological Survey has a seismic station located near Tsumeb.
Of the 60 infrasonic stations around the world, six are in Africa, Namibia has one, which is located near Tsumeb. This station is operated by the Geological Survey of Namibia. The infrasonics device is fairly simple, consisting of five individual arrays of tube networks that are connected to sensitive low-frequency microphones. Signals from all the stations are sent to a central computer where they are analysed and transmitted digitally to the CNTBT headquarters. The complicated network of tubes at each array is individually fine-tuned to filter out any subsonic noise originating from local pressure changes such as wind and nearby industrial activities. These are then linked to computers, which send the signals to Vienna.
The infrasound network detects very low sound waves (.02 to 10 Hz with periods from 0.1-50 seconds) that are below the range of human hearing. The system was designed to detect all explosions greater than a 1 kilometer nuclear explosion, which creates a signal with a predominate period of five seconds or 0.2 Hz. Normal audible sounds will travel only relative short distances. However, scientists have found that there are two sound channels in the upper atmosphere that can carry infrasound very well. A lower one at 20 kilometers high is not effective at carrying sound great distances, but the higher one at 100 kilometers can carry sound around the world. When an above-ground explosion occurs,. seeps back to ground level as the wave travels along. As the sound travels back to earth, the sensors can detect both amplitude and arrival direction.
The system cannot detect illegal underground blasts unless there is a collapse of the earth into the blast cavity or a venting. The Fairbanks, Alaska station is able to calibrate its signal from blasting operations at a nearby gold mine that sets off a 30,000 pound explosion of dynamite daily. In 1980 the Chinese detonated a large nuclear weapon at Lop Nor. The Fairbanks station located 7,237 kilometers away first detected an explosion after 12 hours of travel time. The signal continued for a long time, but it soon became obvious that is was a nuclear blast. The Antarctic station, 14,185 kilometers away, also recorded that blast.
Even though Namibia is a relatively new African nation, its citizens can be proud that their country hosts two of the world’s monitoring stations for the Comprehensive Nuclear Test Ban Treaty and that it is a strong supporter of the ban on nuclear testing