Onshore analogues North Iceland
North Iceland - a fantastic natural laboratory for viewing active volcanic and tectonic processes. IODP Exp. 396 post-cruise field trips.
Iceland is a fantastic natural laboratory for viewing active volcanic and tectonic processes. Northern Iceland has much to offer regarding subaerial examples of geological features encountered and sampled during Exp. 396, including active hydrothermal systems, carbon capture and storage initiatives, geomorphological features, and other spectacular outcrops. During this two-day field trip, we will visit analogue sites in North Iceland from Eyjarfjörður to the Northern Volcanic Zone within the active rift zone of the Mývatn and Krafla areas and the lava fields within the Aðaldalur valley towards the Skjálvandi Bay close to Húsavík.
Iceland's unique geological setting makes it a remarkable place for studying and experiencing volcanic activity. Its location at the Mid-Atlantic Ridge, where the Eurasian and North American tectonic plates diverge, results in extensive volcanic activity due to the rising magma from the mantle. This tectonic boundary is one of the few places where you can see the Mid-Atlantic Ridge on land, unlike most of it, which lies under the Atlantic Ocean. The presence of the Iceland mantle plume beneath the island further intensifies volcanic activity. Mantle plumes are regions of hot, upwelling mantle material, and when combined with the spreading ridges, they create a hotspot of volcanic and geothermal activity. This combination explains the large number of volcanoes and geothermal features in Iceland, like geysers and hot springs. Iceland's volcanic zones contain en-echelon arrays of volcanic systems, such as the Northern Volcanic Zone. These systems consist of central volcanoes, calderas, and associated fissure swarms. The fissure swarms are long eruption fractures through which lava can emerge, sometimes resulting in large-scale eruptions like those at Leirhnjúkur during the Krafla rifting episode in the 18th century or between 1975 and 1984 (e.g., Sæmundsson, 1974; Einarsson, 1991; Hjartardóttir et al., 2012); etc.), or the more recent eruption at Fagradalsfjall in 2021. Understanding Iceland's geology ( https://arcgisserver.isor.is/ ) provides insight into plate tectonics, volcanic processes, and the dynamic nature of the Earth's crust (Jóhannesson and Sæmundsson, 1998; Hjartarson & Sæmundsson, 2014). Additionally, it underpins Iceland's renewable energy infrastructure, which relies heavily on geothermal energy derived from this volcanic activity.
The oldest rocks in Iceland are exposed along the coast in the Northwest, East and central north Iceland ( https://arcgisserver.isor.is/ ) (Sæmundsson, K., 1974). Present-day volcanic activity is confined to the neo-volcanic zones trailing the island. In the southwest, the volcanic zone is a landward continuation of the Reykjanes Ridge. To the North of Iceland, however, the Kolbeinsey-ridge is offset to the West by about 120 km, compared to the volcanic zone in North Iceland. The Tjörnes fracture zone connects the two. It has been suggested that the so-called Eastern volcanic zone in south-central Iceland is a propagating rift.
Active central volcanoes are only found in the volcanic zones, e.g. Krafla, Askja, Kverkfjöll, etc. Swarms of faults and fractures characterize the structure of the Northern Icelandic volcanic zone. Most of them are arranged in an “en echelon” pattern sub-parallel to the direction of the volcanic zone. In the centre of each swarm, a central volcano may develop, characterized by high volcanic activity, silicic rocks, and high–temperature geothermal fields. The central volcano may develop a caldera, e.g. Askja and Krafla.
The climate in Iceland during the late Tertiary period has been documented through rather scarce occurrences of fossilized plant and animal remains. The results suggest a relatively warm climate in the early Miocene about 15 million years ago, with the possibility of a maximum mean temperature as high as 15°C, compared to 4.5°C today. It was comparable to the present-day climate in coastal North-East America and the European mainland. At this time, Iceland was largely covered by leaf-forest (e.g., Denk et al., 2011). The climate was humid, warm and temperate; summers were warm, and the temperature in winter rarely dropped below 0°C. About 8 Ma years ago, the mean temperature dropped to 10°C and continued to drop gradually over the next 4-5 million years. Because of this cooling, the leaf forests were replaced by conifer forests about 7-8 million years ago.
About 5 Ma ago, in the Pliocene, the climate was similar to that we know from the west coast of Europe today. The temperature of the coldest month was 0°C, and grassland became more common, replacing conifer forests. Signs of Iceland's first full glacial-interglacial cycle are dated at about 2.6 Ma. However, glacial sediments can be seen in mountain areas of North East Iceland and in other areas that date back to 4 Ma ago. In the last 2 Ma (quaternary), several glacial-interglacial cycles are recorded. The last glacial maximum was followed by an extended warm period that reached a maximum of about 5.000 years ago. A birch forest covered the country again, up to 60% of the land. The climate cooled gradually from 2500 B.P., glaciers advanced, and forests declined.
The two-day field trip will lead us from Akureyri to the Northern Volcanic Zone, the Myvatn and the Skjálfandi Bay (the shacking bay) areas. We will cross from the Miocene Plateau Basalt domain into the active Northern Volcanic Zones. This will allow us to observe the morphological changes from subaerial shield volcano landscapes to subglacial eruption deposits, fissures, and explosive eruption deposits within the Krafla caldera region. Specifically, the Myvatn area is a natural analogue for shallow water and lava flow interaction that resulted in a unique landscape of pseudo-craters and lava forms. Furthermore, we will visit the geothermal power plant in the Krafla high-temperature geothermal field to learn about the long-standing production history and challenges of geothermal energy production and volcanic reservoir behaviour. We finish our excurse in the Skjálfandi Bay and the Aðaldalur, where we will visit the transition from a regionally extensive lava flow from the Myvatn area through a glacial valley into the river and lake environment of the Laxádalur and out to sea across the river delta plain of the Skjálfandafljót in the Aðaldalur. Thus, this makes this a unique onshore analogue that allows us to observe the different lava flow and physiographical environment interactions.
The only geothermal waterfall in Iceland that leads ~50°C hot water from the Vaðlaheiði tunnel into Eyjafjórður, cascading across a complex NNE-SSW striking dyke system. (Photo: Anett Blischke)
Dimmuborgir
A typical and still preserved example of the complex Dimmuborgir lava tunnel system, located along the eastern shores of Lake Mývatn. (Photo: Anett Blischke)
Lava flow boundaries - Millilög
A typical example of a "millilag" an inter-basaltic sediment bed that is typical for the Miocene Plateau Basalt sections and can contain valuable plant records to aid with geochronology, climate, or paleo-environmental studies. (Photo: Anett Blischke, Eyjarfjörður)
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