The Black Waterfall

22 September 2016

You are a surface geomorphologist. After a long strenuous uphill hike, imagine sitting and relaxing at the foot of a breathtaking waterfall surrounded by basaltic lava pillars with a field notebook in one hand and a rock pick in the other. Something about this geologic wonder seems almost satisfying as if it is a rewarding reflection of your uphill struggle.

This is the exact impression that geologists, tourists, and hikers are likely to experience when they set foot on Svartifoss. Svartifoss is an Icelandic waterfall found in Skaftafell in Vatnajökull National Park, Iceland. Formed in the midst of a volcanic eruption with a quick cooling environment, Svartifoss was given the name “Black Falls” due to its prominent structural features, which consist of dark, hexagonal basaltic lava columns surrounding the overhang and backdrop of the falls illustrated in Figure 1 (Mallet, 1875).

Figure 1: A panorama shot of the Svartifoss outcrop showcasing basaltic lava pillars that are approximately 40 to 50 metres in height (Photo by: Chimira Andres)

Naturally, scientists have studied this site for several decades and research regarding its formation has been compiled continuously until today to determine the overall process of this natural phenomenon. Before Svartifoss formed within the boundaries of the conservation park in Skaftafell, it once was a major farm with a great agricultural histroy. However, the eruption of a subglacial volcano, Öræfajökull, in 1362 wiped out the livestock and surrounding community entirely (Sharma et al., 2008). As the farmers tried to settle back on their land, the cooling climate and lithifying magma made it too difficult to re-establish their farms. With this, lava was rapidly cooled, glacial melt water outflowed in high velocities, and Svartifoss was formed with highly extrusive, igneous-based rocks (i.e. hyaloclastite, basalt) (Hetényi et al., 2011).

The shape and orientation of these pillars is caused by the naturally occurring structure of basalt itself and the direction of magma flow (Tanner, 2013). By definition, basalt is a fine-grained, aphanitic rock that is black in colour. The hexagonal shape of these pillars (shown in Figure 2) is due to the jointing and contraction of the cooling lava bodies as the basalt fractures propagate throughout the different points of the rock (Hetényi et al., 2011). Subsequently, pillars form perpendicular to the surface of the lava flow, growing both from the top surface and also from the base, which is why when lava flows along the horizontal edge of the Skaftafell’s volcanic field, the pillars slowly cool in a vertical fashion, downwards due to gravity (Christensen et al., 2016).

Figure 2: The uneven, hexagonal shape of a columnar basalt that was cut laterally to show perspective from a bird’s eye-view (Tanner, 2013).

Due to the growing presence of this site, these basalt columns have provided inspiration for Icelandic architecture, particularly in the Hallgrímskirkja Church and the Harpà Symphony Orchestra Theatre in the city capital, Reykjavík (shown in Figure 3). With this, geologists and tourists are also commonly attracted by Svartifoss because of its uniqueness to Iceland making it one of the many geologic wonders of the world. Without a doubt, it is important to understand the significance of geologic structures, such as Svartifoss as they provide a mirror to the earth’s past that can later be used to explain various phenomena that may arise in the future.

Figure 3: The outside structure of Hallgrímska Church (left) and the stained glass windows of the Harpà Theatre (right) analogous to basaltic lava pillar features found in South Iceland (Photos taken by: Chimira Andres, 2015).

References:

Christensen, A., Raufaste, C., Misztal, M., Celestini, F., Guidi, M., Ellegaard, C. and Mathiesen, J. (2016). Scale selection in columnar jointing: Insights from experiments on cooling stearic acid and numerical simulations. J. Geophys. Res. Solid Earth, 121(3), pp.1462-1482.
Hetényi, G., Taisne, B., Garel, F., Médard, É., Bosshard, S. and Mattsson, H. (2011). Scales of columnar jointing in igneous rocks: field measurements and controlling factors. Bulletin of Volcanology, 74(2), pp.457-482.
Mallet, R. (1875). Prismatic Structure of Basalt. Geological Magazine, 2(11), p.566.
Sharma, K., Self, S., Blake, S., Thordarson, T. and Larsen, G. (2008). The AD 1362 Öræfajökull eruption, S.E. Iceland: Physical volcanology and volatile release.Journal of Volcanology and Geothermal Research, 178(4), pp.719-739.
Tanner, L. (2013). Surface Morphology of Basalt Columns at Svartifoss, VatnajökulsÞjóðgarður, Southern Iceland. Journal of Geological Research, 2013, pp.1-8.

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