Aldeyjarfoss is regarded by many people as the most attractive and considered one of Iceland’s photographic gems. The setting of the waterfall is unusually beautiful. One of the most interesting features of the waterfall is the contrast between the black basalt columns and the white waters of the fall. (In this, it is similar to the much smaller Svartifoss).
The river Skjálfandafljót drops here from a height of 20 m into a wide bassin in a dramatic gorge. The river has hollowed out many potholes, and the gorge is lined with many impressive basalt column formations. The basalt belongs to a lava field named Suðurárhraun, which was originally formed by eruptions, some 9500 years ago. In Icelandic, hraun simply means lava.
Lava is the name for the molten rock expelled by a volcano during an eruption and also for the solid rock after cooling. The heat of geothermal energy liquefies the rock within the earth. Lava is liquid at temperatures from 700 to 1,200 °C but up to 100,000 times as viscous as water. A lava flow can reach flow great distances before it is cooling down and becomes solid igneous rock.
There are three main types of basaltic lavas (also called mafic lava). Most are ´A´a or Pāhoehoe types, some basaltic block type. These official terms for basaltic lava flows are taken from Hawaii.
(1) ʻAʻā lava (icelandic: apalhraun) is a platy lava flow with a rough or rubbly surface composed of broken lava blocks. (2) Pāhoehoe lava (icelandic: helluhraun) looks has a smooth, billowy, undulating, or ropy surface. This surface develops when very fluid lava is moving under the congealing surface crust. (3) Basalt columns: When a lava flow is cooling rapidly it is shrinking which causes contractional joints or fractures. These columns are mainly hexagonal, but can also have less or more sides.
Basaltic generally erupt at temperatures higher than 950 °C. Basaltic magma contains much iron and magnesium, and less of aluminium and silica. Due to the long distance lava flow basalt lavas build flat shield volcanoes or “flood basalt fields".
Aldeyjarfoss is located in the valley of Bárðardalur about 40 km from Goðafoss, on the edge of the Icelandic highlands. To reach the waterfall, take the 842 road off the ring road 1 km west of Goðafoss. This turns into the 4WD mountain road, F26, towards the end.
From parking lot where you can already see the foss a smoothly descending walking path (T=2.5) of about 5-10 minutes leads you to a viewing area (N 065° 21.962 W 017° 20.295). To answer the questions it is not necessary to climb on the rocks or to go further down to the fall. The rocks can be very slippery. It is up to each one´s own risk to go any further or lower than this upper viewing area.
Questions:
1. Go to the coordinates (viewing area) and look to the far right side of the bassin at the rock wall. There are a few small waterfalls pouring out over a layer of basalt columns. Please describe what kind of columns you see and what do you think caused this appearance?
2. What is another word for “basaltic” lava.
3. Some columns show red colouring. Where does the colour come from ?
4. Make a photo of the waterfall with you, your thumb up or your GPS device and post in the log.
Send your answers to araphoe@web.de . You don´t need to wait for my response to log your find. I will contact you if there is any problem with your answers. Logs without E-Mail answers will be deleted. Do not write the answers in the log.
It would be very kind of you to upload a photo that shows you with your GPS at the waterfall. (This is optional).
Enjoy Aldeyjarfoss and this earthcache !
Sources: Wikipedia and www.visithusavik.com
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