HLJÓÐAKLETTAR (ICELAND) EarthCache
Hidden : 9/5/2012
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:

Your way: Good marked easy path, suitetable even for little children, about 2,5kms long, about 1-1,5h

Approach: Over the F862 (you need a 4*4 for this one).
Parking: at N65.55.860 W016°32.824, WC there

Check the road conditions before setting out for this cache!

Geology:
The Hljóðaklettar (echo rock) is situated in the National Park Jökulsagjlufur. It got its name due to the fact that the sound is reflected from its walls.

The canyon Jökulsárgljúfur is located in the palagonite belt of northern Iceland. The surrounding area is geologically recent, with the oldest surface strata dating from the last interglacial, grey basalt lavas, which flowed from shield volcanoes such as Grjótháls. There exists isolated palagonite mountains (for example Eilífur, 689 metres in altitude, which were formed by subglacial eruptions during the last Ice Age) and several impressive waterfalls such as Selfoss, Dettifoss, Hafragilsfoss and Réttarfoss are part of the river Jökulsá á Fjöllum, which runs through the canyon.

Jökulsárgljúfur and its surroundings are thought to have been cut into the bedrock through a sequence of catastrophic glacial floods, or jökulhlaups, after the end of the last glaciation. The last such flood probably occurred some 2,000 years ago, but the canyon terrain still clearly shows its erosive force.

Geology of Hljóðaklettar:

About 8000 years ago a volcanic fissure erupted, running parallel to today’s river for a distance of some 6 km, producing the two volcanoes Rauðhólar and Hljóðaklettar. At the same time another fissure erupted north of Dettifoss creating the volcano Randarhólar roughly at the same time.
Both fissures produced broad lava fields.
The glowing lava from Hljóðaklettar was drowned by the glacial river. When the lava flow came in contact with the water of the river there had been hugh explosions. But the water had to admit defeat of the power of the volcanic eruption, the explosions decreased in intensity and then the magma flowed slowly out of the volcano. The rock slowly solidified in block lava formation forming in many places basalt columns, partly filled up the river canyon. Afterwards erosion took place and the removal of bedrock was caused by catastrophic floods, washing large parts away, leaving cliff-edged hills behind. Subsequent floods of lesser magnitude, occurring in historical times, have left their marks on the lowlands downstream from the canyon.


In the course of time the tufa layer, which was also created during the volcanic eruption, was digged away by wind-, water- and sand erosion, and the castle like lava formations beneath were layed open. These are now called Hljóðaklettar (echo rocks) consisting of a big labyrinth of caves, vertical cliff formations, rock castles and columnar basalt and basalt rosettes. At some places you can see special erosion effects like the so called honeycomb weathering.

When you hike around the castle like Hljóðaklettar you will see columnar basalt everywhere. So whole area seems be consisting of it. Basaltic pillars evolve during the cooling of a thick lava flow. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it can't easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The topology of the lateral shapes of these columns can broadly be classed as a random cellular network. These structures are predominantly hexagonal in cross-section.

But a lot of these basalt pillars at this place are forming lava roses (= basalt roses = basalt flowers = basalt rosettes = stone roses ...). To be honest I never saw such an amount of lavas roses together in one place.
Lava roses develops when the lava stream forming the columns is not only cooling from one front but from every side around.



This earthcache guides you to the two top places of interest at Hljóðaklettar but the whole area is really worth a visit, you will have fantastic views in all directions after every corner.
The first feature at waypoint T1 is the so called "Troll", a hugh standing rock covered with many basalt roses.
The second one is the so called church "KirKjan", a lava cave at waypoint T2. Use reference point R1 for getting there.
We suggest walking counterclockwise but do as you like it. You are in a national park, so stay on the marked path.

To log this earthcache as a found
you have to send the awnsers to the following questions via GC profile BEFORE online logging. Please log directly afterwards without waiting for logpermission, we will contact you if there will be something sincerely wrong.
1.) How many basalt roses do you count at the "troll"?
2.) Tell me the diameter of the basaltic columns in average.
3.) Explain in simple words why there are so many of these rosettes at this point.
4.) Go inside the cave Kirkjan and observe its ceiling. How many basalt roses do you count here?

5.) Edit 2.8.21: Foto-upload of you, part of you, your GPSr... in your online-log is required (re-allowed by GC since June 2019)

Of course we would be glad about a flood a picture uploads. You can also look out for honeycomb weathering (we were unable to find a place with this special erosional effect during our hike) and post the co-ordinates when you find it.

Sources:
http://www.geysir.com/de/reisefuehrer/dernordosten/staedteorte/hljodaklettar/
http://www.iceland.de/index.php?id=659
http://english.ust.is/media/fraedsluefni/Jokulsarg_ensk.PDF
http://www.vatnajokulsthjodgardur.is/media/nordursvaedi/Jokulsargljufur_baekl_ENS.pdf
http://en.wikipedia.org/wiki/Basalt

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