Jökulsárgljúfur National Park is situated in the north of Iceland around the river Jökulsá á Fjöllum. It lies to the north of the famous Dettifoss waterfall. The National Park is fascinating because of its chaotic canyon and volcanic mountains. The center of the park is Hljóðarklettar (rock of echoes/GC3W6RA). Rauðhólar (red hills) is the most beautiful mountain of the park because of its special colouring.
The way to the earthcache is an extremely varied walk along good waymarked paths with a height difference of 100 m. The roundtrip from the carpark in Vesturdalur to Rauðhólar and back is about 5.1 km. It. takes around 1.15 hrs to get to Rauðhólar and 45 minutes back. You are in a national park, so stay on the marked path.
Approach: Over the F862 (you need a 4*4 for this one).
Parking: at N65° 55.860 W016° 32.824
Check the road conditions before setting out for this cache!
The Randarholar and Rauðhólar crater cones are regarded as parts of the bifurcating Fremrinamur Volcanic System. The Rauðhólar cones and its eroded southern part Hljóðarklettar mark the easternmost branch of the Fremrinamur Fissure Swarm (Fig.1, marked in red) and occur as fissurealigned scoria cones. The approximately 6 km long crater row is aligned NNE, in and along the Jökulsargljufur canyon, while its southern end bends slightly NNW, giving it an arcuate shape. The unglaciated Rauðhólar scoria cones are situated along the narrow river canyon of Jökulsa a Fjöllum, a minor part of the cones are inside the canyon. The Rauðhólar eruption has an estimated early Holocene age of around 9000 years. It is associated with an intracanyon lava flow that fills an area of 2 km², just west of the prominent valley Vesturdalur (Fig. 1). The lava flow stratigraphy there shows that the Jökulsa river cut a canyon, nearly to present depth, before the Rauðhólar eruption.
Figure 1: Detailed geological map of the northern part of the Fremrinamur Fissure Swarm. The
Rauðhólar Cone Row and Hljóðarklettar plugs are highlighted in red.
The Rauðhólar cones are spaced at 200 m in N-S direction und up to 800 m in E-W. The height of the plugs varies between 10 m - 190 m and up to 205 m for the Rauðhólar cones. Several bigger plugs are flanked on their western side by small, aligned dyke conduits, which represent subsidiary vents or lava breakouts. The conduits are elongated in N-S direction, and are funnel-, horseshoe-, and irregular shaped, which indicates an overlapping of cones of the same age.
Rauðhólar has been variably eroded such that, in the northern part, the original scoria cones are preserved, while the central and southern parts expose their shallow feeders. The southernmost part contains only plugs and necks with a thin pyroclastic cover as well as multi-tiered lava flows. The central part combines partially eroded scoria cones, (feeder) dyke intersections, and welded scoria interbedded within rootless and clastogenic lava flows; the welded scoria is composed of different kinds of lithics and bombs. The northern part preserves almost intact, overlapping scoria cones with voluminous lapilli-sized scoriaceous deposits (fig 2).
Figure 2: Lithofacies of fallout deposits
(A) Elongated Rauðhólar scoria cone. Pyroclastic beds are visible on the outer hinge, see person for scale. Jökulsargljufur canyon is in the background.
(B) View into eroded part of scoria cone. 1 m thick pyroclastic beds alternate with fall-out
deposits.
(C) Inclined sheet above fall-out deposits ranging from scoria lapilli to smaller bombs, reflecting Strombolian-type eruption.
(D) Layered scoria-cone deposit. Scoria lapilli, fluidal-elongated small bombs and fragments of juvenile rocks. Compass for scale, close-up view in E indicated by square.
(E) Close-up view of (D) showing scoria lapilli, fluidal small bombs and fragments of juvenile rocks.
(F) View north-northwest inside of the Rauðhólar cone, exposed by river outbursts. Columnar lava flow showing prominent entablature structure.
To log this earthcache as a found
you have to send the answers to the following questions via GC profile BEFORE online logging. Please log directly afterwards without waiting for log permission, we will contact you if there will be something sincerely wrong.
Logs not accompanied by email the same day will be deleted per earthcache rules. I don't like doing that. But you need to complete the requirements. The questions are not difficult and are designed so that anyone can fulfill them.
1: Lightly feel the surface of the tephra and describe the texture of the surface. What does it feels like? Is it smooth, rough, or porous? Explain why it feels this way and what do you think happens if a lot of people walk beside the walking trail?
2: Look at the scoria cone. Is the angle of the steepest slope smaller of larger than 35 degrees? Explain why you think the slope has this angle?
3: If you stand next to the sign and look down to the canyon. You see a beautiful formation on the left just above where the black colour stops. What do you see and how do you think this was formed?
4: We would be glad if you could upload a photo of the beautiful colours and formations but is only optional !!
Sources:
https://www.vinirvatnajokuls.is/media/3065/en_north-area.pdf
https://www.stjornarradid.is/library/01--Frettatengt---myndir-og-skrar/UAR/unesco-nomination-of-vatnajokull-national-park-dynamic-nature-of-fire-and-ice.pdf
- From feeder dykes to scoria cones: the tectonically controlled plumbing system of the Rauðhólar volcanic chain, Northern Volcanic Zone, Iceland / Bulletin of Volcanology
- Rother walking guide Iceland