Öxarfjörður Junction EarthCache
Hidden : 9/29/2015
Difficulty:
2 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:

Öxarfjörður lies within an area where the Northern Volcanic Zone (NVZ) intersects the Tjörnes Fracture Zone (TFZ), which is being slipped westwards to the offshore Kolbeinsey Ridge (KR).

The TFZ was formed 6 - 7 million years ago when volcanic activity was transferred eastwards to the Northern Volcanic Zone.The average spreading velocity across the NVZ is 19 mm/year in a direction of 105°. The TFZ is seismically very active, with frequent earthquake sequences which are mostly concentrated on three northwest trending transform zones: The Grímsey Volcanic Zone (GVZ), the Húsavík-Flatey Fault System (HFFS)and the Dalvik lineament (DL). The earthquakes can reach values of 6 to 7 on the Richter scale. Volcanic systems within the NVZ and GVZ are Fremri-Námar, Krafla, Þeistareykir, Mánáreyjar, Nafir, Hóllinn and Stóra-grunn. The results of which can be observed in numerous places in Öxarfjörður.

At least three volcanic systems stick with their swarms of faults and fissures in the active zone in Öxarfjörður: the 70 - 80 km long and 7 - 8 km wide Þeistareykir, the 100 km long Krafla and Fremrináma fissure swarms. They control the occurrence of geothermal and cold springs in the area. Open fissures and fault scarps belonging to these fissure swarms can be observed in many places along the road. Earthquakes are frequently felt in Öxarfjörður and the area is one of the most active earthquake zones of Iceland. Part of the earthquakes are associated with widening of the fissure swarms. A large swarm of earthquakes in this area in December 1975 - February 1976 was related to activity of the Krafla volcano and its fissures swarm. The series of eruptions in the years until 1984 were called Krafla fires and are responsible for an expansion of 900 mm of the swarms.

To log this cache please send us your answers for the following questions via the GC-contact form before logging it online. You don´t have to wait for a permission, but we will contact you if there are any problems with your answers.

1. What developed during the swarm of earthquakes in the time between December 1975 and February 1976 and what´s its name?

2. Standing at Stage 2 you find examples of Krafla fissures. Estimate their height and describe their shape. Do you find any diffrence between the left and the right fissure? If so, what do think is the reason therefore?

optional: Please take a photo of you and your GPS and attach it to your log.

Additional Hints (No hints available.)

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