it is Allen Shaw...not Alan, Sorry Allen,
John > Dave, > > Being a former resident of Western PA and now living in Eastern PA...it is > hard to imagine how difficult it would be find a meteorite on the ground > surface in this "jungle" of a state. I would suspect the high amount of > precipitation and the extreme temperatures seen through the year would be > real tough on an LL6 chondrite over a 75 year period. However, if your are > ever looking for a partner to go look...let me know, I'll make plans to be > there if I can. I visit that part of the state quite often to see family, and > for work. > > In our case(here in PA) with an extremely high deposition rate, the effort to > find new specimens would probably be more effective by going door to door and > asking like Nininger in the past, and Alan Shaw and others in recent times. > The use of a metal detector in the know vicinity of the Chicora finds would > be the next best thing. > > Good luck if you get started without me, > > John > > > > > The comment was made that: > > > > "If you want to reduce search time per (cold) meteorite find (i.e. > > non-strewnfield), the #1 factor is "survival time" -- you must > > maximize it any way you can: > > 1. Low deposition rate -- ideally a ~negative~ deposition rate: you'd > > > prefer a surface that is "deflating" > > > > > > 2. Low annual precipitation > > > > > > 3. Minimal human presence" > > > > There is yet another way. Search a known strewn field - not one that has been > > picked over but one that has not. > > > > For instance, there have been 8 falls/finds in Pennsylvania - 3 near my home > > town of Pittsburgh. Not many pieces have been recovered. Barring weathering, > > there is a good chance that these "strewn fields" may yet be fertile, > > particularly for stony meteorites. > > > > The incoming Chicora meteoroid was observed by many in 1938 and calculations > > indicate that the total incoming mass was around 519 tons before it exploded > > about 12 miles up. Only four pieces were ever recovered. I just bet there > are > > pieces yet to be found. When I retire, I hope to search this area - it's my > > square mile!! > > > > Dave P. > > > Hi Norm and List, > > > > > > > As an exploration geologist, I spend at least 15-20 long days every > > > > month wandering the alluvial fans and dry lakes of Nevada searching > > > > for mineralized float (and, unofficially, meteorites!). Some of > > > > the remote dry lakes are almost certainly unsearched, and can cover > > > > many square miles. > > > > > > You might be surprised. Aside from playas on military installations (which > > > in Nevada is a pretty big fraction!) I'm fairly confident that most > > > of the major dry lakes in Nevada (and California) have been searched at > > > least once by one or more competent meteorite hunters. Of course, they > > > haven't been searched "completely"; indeed, no location can ever be > > > completely searched due to the dynamic nature of playas. > > > > > > > Putting along on my ATV, I can give a reasonably large area a pretty > > > > decent search. After several years of this, still NO cold finds. > > > > > > This is actually a bit surprising, though I can think of a couple > > > factors which could bring it about: > > > > > > 1. your size threshold (how small a stone you will stop for) > > > 2. too broad a search image > > > > > > By broad search image I mean that your primary target (mineralized > > > float) is so dissimilar to your secondary target (meteorites) that > > > the subconscious pattern-matching that your brain is trying to > > > accomplish will suffer. (It's hard enough picking out meteorites > > > among terrestrial brown and black rocks). > > > > > > > I think the point may be that there's a pretty good chance that > > > > stones have at some point fallen on most any square mile of earth's > > > > surface. > > > > > > Absolutely. Even if each fall produced only a single meteorite, in > > > any square mile you could expect a fall about once every 5000 > > > years. However, the average number of meteorites per fall is > > > certainly more than one (perhaps in the neighborhood of a half > > > dozen?), so this improves things. Maybe a meteorite every 2500 > > > years per square mile (a complex problem that requires some > > > Monte Carlo modeling to come up with a good figure). This leads > > > to Norm's next point: > > > > > > > However, in most areas, survival times are short. In many areas, > > > > erosion has erased the record. In other areas, deposition has > > > > buried every trace. > > > > > > Exactly. I liked this wording: > > > > > > > From the cosmic perspective, every square mile is created equal, but > > > > for us grunts on the ground, that's far from the case. Some square > > > > miles are just right. Most are not. > > > > > > If you want to reduce search time per (cold) meteorite find (i.e. > > > non-strewnfield), the #1 factor is "survival time" -- you must > > > maximize it any way you can: > > > > > > 1. Low deposition rate -- ideally a ~negative~ deposition rate: you'd > > > prefer a surface that is "deflating" > > > > > > 2. Low annual precipitation > > > > > > 3. Minimal human presence > > > > > > Fortunately point #3 tends to go naturally with #2. It's only in the > > > modern era of weekend warriors (and meteorite hunters!) that #3 has > > > become an issue. Still, the historical importance of point #3 can > > > not be ignored for iron meteorites. Chondrites wouldn't have been > > > > > particularly useful to native Americans 500 years ago; irons certainly > > > were. > > > > > > But detection isn't just about "signal" (signal in this case being > > > the presence of meteorites); it's about signal-to-noise ratio (SNR) > > > and scan rate. What else is sharing space with your meteorites, > > > and how does this impact the rate you can search an area? It's > > > not much fun looking for meteorites in a sea of basalt. > > > > > > Scan rate, incidentally, is the reason one should never hunt cold for > > > meteorites with a metal detector. It is more than 50 times less > > > efficient that visual searching. But you also don't want your scan > > > rate to be too high or you'll miss the small stuff. Remember that > > > there are far greater numbers of small meteorites than large ones. > > > Searching in a car or truck is fine for finding the big ones, but > > > most places that ~can~ be searched by car/truck in Nevada and > > > California already have been. You'll have better luck looking for > > > small meteorites, and this means getting out of your car and its > > > > > limited viewing angles. Most of my searching is done on foot. > > > > > > An ATV is even better than walking: you're still close to the ground > > > with an unobstructed view, but you have the comfort and convenience > > > of motorized transport. ATVs can also get into distant areas that > > > cars can't (and by extension, walking searchers). > > > > > > So to summarize: search old, simple surfaces on foot or by ATV, > > > and you will eventually find meteorites. > > > > > > Cheers, > > > Rob > > > > > > > > > ______________________________________________ > > > Meteorite-list mailing list > > > [EMAIL PROTECTED] > > > http://www.pairlist.net/mailman/listinfo/meteorite-list > > > > ______________________________________________ > > Meteorite-list mailing list > > [EMAIL PROTECTED] > > http://www.pairlist.net/mailman/listinfo/meteorite-list > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
