[meteorite-list] Cold hunting

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:53 2004
Message-ID: <20030911023430.306195368B_at_pairlist.net>

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
> > > Meteorite-list_at_meteoritecentral.com
> > > http://www.pairlist.net/mailman/listinfo/meteorite-list
> >
> > ______________________________________________
> > Meteorite-list mailing list
> > Meteorite-list_at_meteoritecentral.com
> > http://www.pairlist.net/mailman/listinfo/meteorite-list
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://www.pairlist.net/mailman/listinfo/meteorite-list
Received on Wed 10 Sep 2003 10:34:28 PM PDT