Basalt Coast at Arnarstapi EarthCache

Basalt Coast at Arnarstapi

Arnarstapi Coast

Arnarstapi is located on the south side of the Snæfellsjökull volcano and has a strikingly eroded black cliff with caves and rock gates. This can be seen particularly well on a 3 km hike to the neighboring village of Hellmar.
At Arnarstapi, the sea has reshaped the basalt columns on the beach and formed a wide variety of bays and caves that extend under the cliffs. Some of these caves are open at the top and in storms and high waves it foams up from them. Various rock pillars, former lava Channels and remains of craters stand in the sea and serve as nesting sites for the numerous sea birds. Above all, one can find black-backed gulls, kittiwakes and fulmars here. Many arctic terns also nest here.

Basalt

Basalt is created when the earth's mantle melts. Thin, low-SiO2 magma cools relatively quickly on the earth's surface or in the ocean when it emerges into basaltic lava. When they emerge, the magmas usually have temperatures between 900 degrees Celsius and 1200 degrees Celsius, depending on their chemistry. The magma is usually not 100% liquid, there are often inclusions (xenocryst) of minerals or whole rocks (xenolite) with a higher melting point, which were carried away during the ascent.
Basalt is the most widely distributed rock, both on the continent and at the bottom of the ocean. Of these, the tholeiitic basalts, named after the town of Tholey in Saarland, form the main part of the oceanic crust and a number of occurrences of the continental crust.
Basalt is usually dark grey to black. Since it arises volcanically, it consists for the most part of a fine-grained matrix due to the rapid cooling. Larger crystals that can be seen with the naked eye are relatively rare, but can be more common in some basalt varieties.
The appearance of cooled basaltic lava depends mainly on two factors. Erupted lava cools down very quickly to form a coherent rock structure, which solidifies as Pāhoehoe lava or Aa lava, depending on the temperature and gas content. However, if the cooling takes place with a delay, the contraction often results in meter-long angular basalt columns (columnar basalt) that are perpendicular to the cooling surface, preferably with a hexagonal geometry.

As molten rock cool below ground, they may shrink, forming joints.

Most commonly, columnar jointing is observed in basalt.

A rather seldom appearing form of basalt is spherical basalt, which is preferably found on the edges of basalt deposits.
Basalt often has ferromagnetic properties, as it can contain small amounts of magnetite.

Your task to log the cache:

Answer the following questions via my geocaching profile:

1.) At the coordinates you are standing on a viewpoint platform. Facing the ocean, when you are looking to the right (in direction SW), what two different basaltic features can you observe? Are the columns aligned perpendicular or horizontally? Why do you think it is so?
2.) Facing the ocean, when you are looking to the left (in direction NE), what basaltic feature can you observe here? Tell me the main difference from the right side!
3.) Search near the platform, take a handpiece of the basalt and tell me how it looks like! Do you think it has been cooled down rapidly or slowly?
4.) Optional: Post a photo with your log, showing you and/or your GPS near the given coordinates in the header!


After you've sent me the message with your answers, feel free to log! Only if there's something wrong, I'll contact you via message!

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