5 January, 2003
Metal Detecting in Antarctica
Post by Dante Lauretta
The wind was howling again this morning, meaning that we spent most of the day in our tents. I decided to take this opportunity to write for the website. The 2002-2003 ANSMET season is rapidly coming to an end. It is hard to believe that we have been on this continent for more than six weeks now. Everyone agrees that this season has been a great success. At last count we had well over 440 meteorites. Most of these have been found in moraines, which are concentrations of rocks deposited along the edges of moving glaciers. In the moraines that contain a lot of meteorites there are also many other different types of rocks. These rocks come from all over Antarctica and in some cases have been transported for hundreds or thousands of miles. The moraines are the most difficult areas to search for meteorites because, unlike out on the blue ice, there are thousands of terrestrial rocks for every meteorite.
This season was the first in many years in which a metal detector was used to help in the moraine searches. Metal detectors are used by many professional meteorite hunters around the world. However, a metal detector had not been used on an ANSMET expedition since the mid-1980s. The metal detectors of this era did not perform well in the Antarctic moraines because of the wide variety of highly mineralized rock types, all of which produce a response similar to that of a meteorite on these metal detectors. However, since this time there have been many improvements in metal detector technology, the most important of which is the ability to "ground balance" or cancel out the dominant background rock. This feature greatly improves the ability of a metal detector to find meteorites in glacial moraines. I have been interested in metal detecting for several years and asked Ralph Harvey if I could bring one along on this trip to test its ability to detect different meteorite types.
It is important to remember that only certain types of meteorites can be found with a metal detector. In parcticular the ordinary chondrites, certain carbonaceous chondrites, and iron meteorites can be detected. Other carbonaceous chondrites, achondrites, lunar meteorites, and Martian meteorites do not contain enough iron metal to produce a response. Thus, there is an inherent bias in the meteorites that one can find with a metal detector. Even for the meteorite types that can be detected, it is not as easy to find them as some people think. The metal detector produces a constant hum, not unlike that of a small fly in your ear. The pitch and volume of this hum increases when a metallic object is under the detector's coil. Because of the wide variety of rock types in the moraines the ground balancing can only cancel out some of the rocks. Other mineralized rocks, known in the metal-detecting world as "hot rocks", will still produce a signal on the metal detector. Thus, metal detecting requires a lot of concentration. You have to listen to the audible signal of the detector, examine every rock that produces a signal to determine if it is a meteorite or a hot rock, and keep your eyes open for any interesting meteorites that the metal detector can not find. On the other hand, metal detecting in Antarctica is much easier than in most other places in the world for one reason: there is no trash out here!
The metal detector has been used in every moraine that we have searched this season, with varying degrees of success. On one day we hit a large concentration of ordinary chondrites and found twenty meteorites in the span of four hours. On other occasions the metal detector had been used all day only to find one or two meteorites. Some areas are loaded with so many different types of hot rocks that it becomes impossible to find the meteorites among them. We have also covered ground that contained many meteorites which for one reason or another did not produce a response on the detector. These meteorites were only found by painstakingly searching every square inch of the moraine on foot. In some areas we had to get down on our hands and knees to find tiny meteorites hidden among the other rocks in the moraines.
There is no doubt that the metal detector has contributed to this year's meteorite recovery. So far over 60 meteorites have been found in the moraines with this technique, many of which were buried under several inches of snow. Thus, the metal detector can find meteorites that would be missed by foot searching and foot searching moraines has produced meteorites that could not be found with a metal detector. It seems that the best way to recover meteorites from these areas is to use a combination of metal detecting and good old-fashioned foot searching.
The wind didn't abate much this afternoon but most of us had developed enough "tent fever" to be willing to work for a few hours. We left camp around 2 pm and decided to finish a few odds and ends nearby. We finished a search of a nearby moraine which we call "That Moraine" and found five more meteorites including two by metal detecting, which were buried in snow. We systematically searched a small ice patch between the moraine and the large ice sheet called Lower MacAlpine Hills. This search yielded one more meteorite. We continued to search the ice around That Moraine, slowly working our way back to camp. We ended the day with seven new meteorites, bringing the grand total to 444. As I finish writing this message the wind is getting stronger, making it seem doubtful that we will be able to work a full day tomorrow. However, the weather around here is difficult to predict and all of us hope that morning will bring the clear skies and gentle breezes that we were blessed with for most of the season.
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