Edit 25.11.2011: Logging requirements modified!
Bartolomé is a small island belonging to the Galapagos islands. This Earthcache will guide you along the two visitor places on that beautiful island.
General informations of Galapagos’ Geology:
The Galapagos islands, which belong to Ecuador, are a group of volcanic islands located on the equator in the pazific ocean only 1000km west of South America. Like many oceanic islands (such as Hawaii) the Galapagos islands are thought to be situated on a „hot spot“ in the earth’s crust, a structural weakness of the mantel plume where magma flows through the solid plate, building volcanoes when it does this. The plates of the earth's crust (Galapagos is lying on the Nazca Plate) float on the mantle, slowly moving in the process known as Plate Tectonics. As a result, the volcanoes of the hot spot seem to appear in different locations over the time.
In the case of the Galápagos, the oldest islands are to the east (Española (5 million years old)), even older islands (nine million years old) are submerged 2km below the surface. On the other hand the newest island (Fernandina, only hundreds of thousands years old) is the most volcanically active (last eruption 1994). The hot spot is now under Isabella and Fernandina.
Most of the islands of the Galápagos are formed around single shield volcano cones (exception for example Isabela made up of six volcanoes).
But after growing through volcanic activity, erosion take place. Since the islands of the Galápagos are situated in the middle of the sea, the primary force of erosion is water. Tide and storm wash the shores of the islands even as the volcanoes build them, and the shape of the cliffs becomes changed, according to the composition of the rock. Soft volcanic ash such as tuff or pumice erode quickly into more gentle shores, while harder and newer basaltic flows form rugged, steeper island walls. The softer soils of Bartolome create a rapidly-eroding landscape, with a long sandy beach (partly filled by the prevailing southwesterly currents and winds). Other important erosional tools are rain, wind and storms.
Bartolome:
The little island Bartolome is only 1,2qkm small (900m*2220m) and 114m high situated close to Santiago Island. When the volcano that formed Bartolomé erupted, there was not any water present resulting in large amounts of basalt on this island (when water is present in an eruption tuff is created). The basalt hardened together with air creating very light rocks.
Bartolome’s surface is covered with volcanic ash, which is suposed to be blown over from Santa Cruz Island. The island consists of an extinct volcano and volcanic formations in a variety of red, orange, green, and glistening black.
Pinnacle Rock is the eroded remains of a tuff cone. This large partially eroded lava formation was created when magma expelled from the volcano reached the sea. When the seawaters cooled, the hot lava caused an explosion. The exploded particles eventually fasten together forming a rock composed of thin layers. Bartolome's Pinnacle Rock has become one of the most photographed sights in the islands. As a prominent landmark it was used as a target for US military during World War II (you can still see the bullet holes). Galapagos Penguins are living behind the rock. A small submerged crater can be seen just offshore. To the east you can see a series of small spatter cones. Lying beside the Pinnacle Rock are twin half moon shaped beaches. On the northern one (wet landing) you are allowed to swim and snorkel. Don’t miss that!
A trail leads you across a sandy isthmus (vegetation: mangroves) to the other half moon shaped beach at the southern side (approx. 120m). Swimming is not allowed there, because White tipped sharks live close to the beach. Watch out for ghost crabbs.
The second way to enter Bartolome starts with a dry landing in the North. Watch out for little submerged crater at the landing spot. The path is about 600m long and you will need half an hour for it. The trail begins with a rock but then you have to walk through volcanic sand. A wodden stairway (~360 steps) will bring you through the lunar landscape with almost no visible pionier vegetation up to the summit hill (altitude 114m) and the viewpoint. From there you will have -looking in direction southwest- the „classic view“ of Galapagos: the two half moon shaped beaches, Pinnakle Rock, turquois water and Sullivan Bay (Santiago) in the background.
While walking up the hill you can see a lot of volcanoes features:
1.) Lava tubes: These are formed by flowing rivers of lava whose outer surface cooled and solidified quicker than the insides (creating a skin) while the liquid lava continues to flow through the middle, hollowing out an area creating a tube like structure especially when the inside lava kept flowing until the tube emptied itself. These tubes could be seen in lines down the mountain.
2.) Spatter cones: You can see those cones in deep red, gleaming black or intense greens at both side of the trail. These cones are formed when there is pressure below magma in an active lava flow, and the gases there push upward. The gases escape and carry big pieces of lava into the air where the outside of the lava ball cools down and turns black. Gravity pulls the lava down, and when it hits the ground, the lava ball bursts open, releasing the still hot magma inside.
3.) Lava bombs: These are the outcomes of a spatter cone. The outside of these "bombs" are smooth, but the insides when it burst are broken, creating Aa lava. The broken lava, aa, is very runny and breaks and rolls once burst. However, once the gases all escape, then the lava will start to slow, creating pahoehoe.
Attention: Stay on the path and do not hurt the National Park rules!
The listing coordinates seems to be a little out of the trail, don't bother, just stay on the path!!!
For fulfilling the log-conditions you do not need to have a GPSr with you.
To log this cache as a found, you have to
1.) climb up the hill and make a photo of you in front of the „postcard view“ which you upload in your log (optional since 1.1.2011).
2.) Look around while climbing up. You will find all of the three descripted volcanoes features easily. Make a photo of one them and upload it in your log too (re-allowed by GC since June 2019).
3.) Contact me via geocaching and tell me what geological feature you will find under water, directly at the jetty.
If your trip does not include the hike up to the summit of Bartolome, you can log this cache as a found by
1.) taking a picture of you at the beach in front with pinnacle rock in the background, which you upload in your log (re-allowed by GC since June 2019).
2.) Draw a scetch of Pinnacle Rock and the bay while standing on the beach which you upload too in your log (attention: it is a wet landing)
3.) Contact me via geocaching and tell me the name of the grey pionier plant which grows up the hill (your tourguide may help you).
Logs without the required upload or the awnser to the question via e-mail will be deleted. Due to "administration" of the log-permissions it is nessecary that every team send an e-mail by itsself even if you were there together. Do not wait for log-permission, just log your found directly after sending the mail; we will contact you if there is something wrong.
Old holiday logs are wellcome if you can still fulfil all three log-conditions (the picture must show you at a typical recognisable spot on Bartolome).
If you shot nice photos of Bartolomes flora, fauna or geology please load them up too.
And your favorite ones of the whole Galapagos trip are wellcome, too. Please note where the photo was taken.
For further and much more detailed information about Galapagos’ geology visit: http://www.geo.cornell.edu/geology/GalapagosWWW/GalapagosGeology.html
Book recommendations (field guides of Galapagos):
• Collins, Safari Guides: Wildlife of the Galapagos (Fitter, Fitter & Hosking), HarperCollinsPunblishers, London 2000
• In German: Pölking, Fritz: Nationalpark Galapagos, Das Naturparadies im Stillen Ozean, Kilda-Verlag, Greven 1989
• In German: Bittmann/Fugger: Reiseführer Natur: Galapagos, BLV, München 2002
Quellen:
http://www.doc.ic.ac.uk/~kpt/terraquest/galapagos/atlas/geology/geology.html
http://www.geol.umd.edu/~jmerck/gal04/events/htmls/dauttl.html