Penedo do Lexim Earthcache EarthCache
Penedo do Lexim Earthcache
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Difficulty:
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Size: 
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Penedo do Lexim (Lexim’s Rock) is one of the extinct volcanic
chimneys of the so called Lisbon’s volcanic complex. It is
nowadays classified as of public interest. To do this cache don't
look for a container, but bring a camera with you (read description
below).
Taking a look around Lexim’s Rock, and despite the
low-mountain area that surrounds us, the calm and colourful scenic
view we admire (the green fields, Cheleiros village down in the
valley, the main road some distance away, the little farms all over
the place, the silent power plant windmills) may lead us to think
we are facing a landscape that has always been like that. That, if
any change would have happened, those would only been small and
neglectable. But remember you are only on top one of the many
volcanoes that actually shaped this landscape over 70 Million years
ago. If by any chance you would have passed by then, you would have
found a very different scenic view, that would have made you
remember that the ground in which you step daily is part of a
ever-changing globe – only at a timescale incomparably larger
than our memory can even understand.
Measuring 230 metres high on its peak, this hill originated on the
end of the Mesozoic period, around 72 Million years ago, in a
strong volcanic activity period (‘Volcanic chart’
figure). What we can see nowadays is part of the remaining volcanic
chimney, namely the solidified magma material, stronger, that
survived the natural erosion process (and the former stone quarry
that operated in this place…) of the last 72 Million years
(‘Erosion chart’ figure). Studies indicated that this
chimney originally was 30 metres in diameter and 2000 metres
deep.
Basalt shows its presence here, and you should observe hexagonal
basalt prisms (resulting from the magma cooling process) and
several crystals.
To log this cache you need to:
- measure the prismatic forms in the fallen basaltic column in this
location (cache's coordinates) (note: You don't actually need to
measure every single one of them, they are quite similar);
- find why does lava assumes a prismatic form when it cools down
(you will not find information in the location, you will need to
chase it somewhere else);
- mail me both answers;
Please include a picture of yourself and some of the prismatic
basaltic forms on the cache's coordinates in your log. You may also
admire more of those at the stone quarry area (N38º 53.549
W009º18.670).
VERY IMPORTANT NOTICE:
- Park the car and go directly to the mentioned coordinates,
following the trails (the path is pretty obvious). Do not approach
the hill's peak (N38º53.529 W009º18.677) nor South Face, due to the
archaelogical sensitivity and importance of discoveries made on
that area. If you stay by the mentioned path and given coordinates,
you can still admire this ancient volcano without endangering any
archaelogical feature.
Information and charts extracted from Ciência Viva
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Geocaching in
Portugal
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