Karst limestone, caves, sinkholes, and radio telescopes

We drove the back roads of Puerto Rico from our house in Aguadilla on the northwest coast to the Arecibo observatory the other day, and decided we love everything about this place: the climate, the food, the people, and definitely the scenery.  This area of PR is composed of karst limestone, which is ancient sea floor being slowly dissolved by the acidic water flowing through it.

A good example of the "holey" limestone that makes up the karst substrate of most of western and west-central Puerto Rico.

A good example of the “holey” limestone that makes up the karst substrate of most of western and west-central Puerto Rico.

When the erosion occurs from underground water percolation, it can excavate huge underground spaces, leaving cavernous cave rooms.

Dragon's mouth entrance to Rio Camuy cave features a set of fearsome stalactite teeth from its roof.

Dragon’s mouth entrance to Rio Camuy cave features a set of fearsome stalactite teeth from its roof.  The underground cavern here opens up to the light from a sinkhole where the cave ceiling fell in.

When the porous limestone roof becomes too thin to support its weight, it collapses, forming a sinkhole, and carrying everything on the surface into the cave system with it.  Sinkholes are conspicuous circular depressions, looking like bowls, covered with forest vegetation.  One such depression south of the town of Arecibo, P.R. caught the eye of some Cornell scientists back in the 1960s who decIded that the particular sinkhole was the perfect spot to build the world’s largest radio telescope.

The spherical collector of the radio telescope is 1000 feet in diameter.  A special focusing

The spherical collector of the radio telescope is 1000 feet in diameter. A special focusing receiver (weighing 900 tons) is suspended above the collector by 18 cables, 6 from each of three 300 foot towers.  The entire structure was too large to photograph, even with my wide angle lens.

Although it was originally designed for research on the earth’s atmosphere, minor alterations in the collector and receiver structures have enabled the largest radio receiver in the world to explore the electromagnetic radiation of the planets of this solar system as well as distant ones in far-off galaxies.

all because there was an underground river carrying acidic water through an ancient sea bed…

Bougsinvillea grows luxuriantly everywhere, including the Arecibo visitor center

Bougsinvillea grows luxuriantly everywhere, including the Arecibo visitor center

2 thoughts on “Karst limestone, caves, sinkholes, and radio telescopes

  1. When I read your title, I wondered how you were going to tie together all of those elements into a single posting, but you managed to do so really well. The porous limestone is fascinating to learn about and see. It incredible to think that someone looked at a hole in the ground and thought, “This looks like a great place for a radio telescope.” Ah, those crazy 1960’s.

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