Geology Reference
In-Depth Information
2.3.1. Reconnaissance Procedures
examined and allows the visit to do more than establish
the presence or absence of meteorites; the full scope of
the concentration can often be gauged. These extended
first visits therefore often lead to some important decision
making for ANSMET. Sometimes a two-person field
party will find too few meteorites to support full-scale
systematic recovery, and under those conditions the team
may try to complete systematic recovery themselves.
Examples of this kind of action from recent ANSMET
history include the icefields near Bates Nunatak,
Lonewolf Nunatak, and in the Geologist's Range.
Similarly, an icefield may be considered “uneconomical”
for other reasons, such as a very low concentration of
meteorites, or an overwhelming abundance of terrestrial
rock that compares poorly with other known icefields
where recoveries are easier. The best situation is when the
team quickly encounters large numbers of meteorites,
immediately proving the need for large-scale systematic
recovery. Having met the primary goal of reconnaissance,
that team will typically move on to new targets as soon as
possible. Nature, of course, has provided us with icefields
exhibiting every level of concentration between these end
members, and as the availability of logistical support and
the demand for meteorites change, some icefields thought
uneconomical by earlier explorers may be targets of
systematic work in the future.
The goal of ANSMET reconnaissance work is to deter-
mine whether a blue ice area harbors a meteorite
concentration, and if so, to understand its full extent.
While individual rocks can be seen from the air (even
satellite-based imagery can now pick out rocks in the 10's
of cm range), determining the nature of these rocks
(extraterrestrial or otherwise) still requires a personal
visit. Reconnaissance visits typically take a variety of
forms in a hierarchy of effort levels, from first visits to
full-scale expeditions (Figure 2.2 a and b).
2.3.1.1. Early visits.
Even a single meteorite find can
prove the value of the site to ANSMET and serve as the
impetus for future larger-scale recoveries. As a result (and
given time constraints) the goal for most early visits is to
examine as much high-priority blue ice as time and equip-
ment allow. Often the first visit to a site will occur as part
of a long day trip, where icefields within reach of an
existing ANSMET camp are visited by snowmobile and
examined for a few hours. Day trips are fairly common
during the early sessions of systematic searching at a
given icefield, since they are easily supported by the larger
field team and fuel supply associated with such a camp.
These efforts can also be very effective; day trips taken
during the early years of systematic searching at the
Lewis Cliff Ice Tongue led to the discovery of several
additional meteorite concentrations in the Walcott Névé
region, including the Foggy Bottom/Goodwin Nunatak
and MacAlpine Hills icefields, home of the QUE and
MAC meteorites, respectively. Thus a few reconnaissance
day trips more than tripled the number of specimens
recovered in the Walcott Névé region. Aerial support has
also been effective in spite of obvious limits on the
number of people and amount of equipment that can be
transported. The first meteorite concentrations discov-
ered by ANSMET in the Allan Hills region were all found
during helicopter-supported day trips, as at the Lewis
Cliff Ice Tongue and the Miller Range icefields about a
decade later. Similar day trips, supported by helicopter or
Twin Otter, take place whenever aerial support and
potential targets coincide.
When a target icefield is simply too distant to be visited
without an overnight stay, the need for increased survival
gear scales up the complexity of a reconnaissance visit.
For such visits ANSMET will typically send a team of
two equipped with snowmobiles and survival gear
sufficient for several days. Many major meteorite concen-
trations were first explored through two-person visits;
notable examples include the LaPaz icefields, first visited
in 1991, and more recently the Buckley Island icefields.
The additional time and mobility available during such
visits dramatically increases the area of ice that can be
2.3.1.2. Large-scale reconnaissance.
ANSMET has
periodically dedicated whole field teams and seasons to
reconnaissance efforts, usually when we have identified a
broad region that contains numerous potential target ice-
fields. Such a season is designed to send a lightly-equipped
four-person team to a number of icefields, either on a
long overland traverse or with extensive aerial support.
Such a season may include opportunistic first visits to
icefields, as well as visits to sites where meteorites
have been previously recovered but the extent of the
concentration (if any) remains unknown.
The amount of time planned for each icefield is esti-
mated from previous visits or its geographical extent,
with visits lasting from a few days to a week or more.
With the many unknowns including rapidly changing
weather conditions and challenging logistical schedules,
preseason reconnaissance plans rarely survive first
contact with the target icefield. We have learned that a
dedicated reconnaissance season requires a very flexible
timeline that allows for dramatic shifts in priorities as the
season progresses. As noted previously, even a single
meteorite find can lead to many days of searching a new
icefield; and on many occasions long days of searching
can lead to few or no finds at all. High numbers of mete-
orite recoveries are not typically expected during large-scale
reconnaissance: the increased number of days dedicated
to travel between icefields alone limits searching time.
