Jan Mayen lies about 550 kilometers north of Iceland and 450 kilometers east of Greenland. It is a strangely shaped island, stretching 53 km long from southwest to northeast. It was discovered early in the 17th century, and is a part of Norway since 1930. In the past, there were several active whaling stations, but now only an active Norwegian military and weather station is present.
The most impressive feature of the island is the 2277 m high Beerenberg, the northernmost active volcano. It is a glacier-covered stratovolcano with a 1-km-wide summit crater and numerous cinder cones. The island rises from a subsea volcanic mountain chain called the Jan Mayen Ridge, which forms the boundary of the 1500-metre-deep Iceland Plateau in the northeast. The oldest rocks which extend above sea level are only around half a million years old, making it a quite young island, having hardly experienced more than the last three Quaternary ice ages.
The bedrock on the island consists of basalt lava flows alternating with pyroclastic rocks. The latter are rocks of volcanic origin flung out during eruptions and more or less consolidated in the air. The youngest volcanic eruptions in 1970 and 1985 took place on the lower slopes on the northeast side of Beerenberg. There is thought to be an average of one volcanic eruption on Jan Mayen every 100-130 years.
Geological map of Jan Mayen (source: www.npolar.no):
Most people who arrive on Jan Mayen will probably do this by boat, and as soon as you set foot on the beach, you will notice that the sand on the beach is black. Black-sand beaches occur worldwide on volcanic islands. They are black because many volcanic minerals and rocks are dark-coloured. Common rock types of volcanic islands are basalt (black when fresh), andesite (usually dark gray) and volcanic glass (often black in color).
Black sand on the coasts of volcanic islands is mostly composed of volcanic minerals and lava fragments. Volcanic sand made up of volcanic minerals is similar to most other types of sand in terms of its formation. However, the composition is generally different, and this type of volcanic sand is typically immature because most of its components are susceptible to weathering. It is often composed of rock fragments rather than individual mineral crystals. The other group type of volcanic sand is composed of volcanic glass, rock fragments, and crystals in all possible proportions.
Black volcanic sands sometimes contain many non-black grains like green olivine crystals, reddish (usually because of weathering) volcanic rocks, light-colored quartz (when the source area is continental) and carbonate biogenic grains (coral sand). Most volcanic minerals are not very stable and decompose pretty rapidly.
Olivine is usually green and mostly present in volcanic sands. It is the least resistant to weathering among the common heavy minerals. Weathered olivine may be brown, orange or yellowish.
In order to log this EarthCache, go to the coordinates posted above (or close enough that you're standing on the black sand beach) and answer the questions below. You can send your answers to me either by email or using the messenger system. You don't need to wait for a response before logging your find, but don't put the answers in your logs or pictures.
Questions:
1. Take a handful of sand and watch it closely. Would you say this sand is fine, medium, coarse or very coarse?
2. Do you think the black sand is composed of volcanic minerals and lava fragments, or of volcanic glass, rock fragments, and crystals? Justify your answer.
3. a. Can you find any other colours in the sand?
b. If so, which mineral do you think this is?
c. Are the crystals larger or smaller than the sand grains?
d. Based on what you see, has this mineral weathered much already? Why do you think this is?
4. (as of March 1st 2020) Add a picture of yourself and / or your GPSr next to the whale bones or the remembrance plate for the Dutch whalers.
Sources:
http://www.npolar.no/en/themes/geology/arctic/jan-mayen.html and www.sandatlas.org