Silfra Fissure is known to scuba divers the world over for the incredible visibility of its glacial meltwater. The fissure, like Nesgjá in the north of Iceland, is located on the tectonic plate boundary of the Mid-Atlantic Ridge. Silfra is also a site that can be accessed throughout the year, as the temperature of the water does not fluctuate by much and remains between 2 to 4 °C. During winter, snow-cover in Iceland is usually quite heavy, and hiking paths are closed off for safety. This makes Silfra a perfect winter option for those who are in search of outdoor activities.The only way to dive the Silfra Fissure is to join a tour from one of the many dive operators in Iceland. The tours that they provide include a divemaster as well as all the gear that will be required for cold water diving, such as a drysuit and a thermal undersuit. The tours can also include a pick-up from (relatively close) Reykjavík, but since the park is located along the Golden Circle route, driving there yourself in a rented car is probably the more exciting and adventurous option. The only dive operator that operates in winter is dive.is, and they also happen to be the longest running dive and snorkel company in the whole of Iceland. If you do not happen to meet the requirements to dive Silfra, dive.is also provides drysuit speciality courses at an additional cost.Requirements:
- You must be a qualified diver with a certification in a drysuit speciality; OR
- You must be a qualified diver with at least 10 logged dives in a drysuit conducted over the past two years, signed by an instructor or divemaster.
Silfra Fissure is located in Þingvellir National Park (Anglicised: Thingvellir), a UNESCO World Heritage Site that was designated in 2004 based on cultural criteria. This is because the park is the historical meeting place of the Viking Age commonwealth parliament, referred to as Althingi . There has been ongoing discussion about a possible "serial trans-boundary nomination" for the Mid-Atlantic Ridge, however, so the park may fulfill the geological criteria at some point in the future. If that happens, Þingvellir National Park would be considered a 'mixed' site and would then be included amongst the Natural World Heritage Sites.The park encompasses Lake Thingvalla (Icelandic: Thingvallavatn), which, at 14-kilometres long and covering an area of 84 square kilometres, is the largest natural lake in Iceland. Only ten percent of the lake's water comes from surface water such as rivers and brooks, whereas the rest of the water originates from springs and fissures on both the bed and the shore of the lake. The underwater catchment area of these springs and fissures extends as far as Langjökull glacier , which is located more than 50 kilometres away.
One of the rivers that flows into Lake Thingvalla is Öxará river. The river meanders towards Þingvellir from another lake called Myrkavatn in the north, and forms a waterfall called Öxarárfoss where the river meets the Almannagjá gorge, which is essentially the eastern edge of the North American tectonic plate. Öxarárfoss, which literally means 'Waterfall in the Ax River', turns out to be a human-made waterfall, as evidence indicates that Öxará river was diverted in the ninth century to channel the water into the gorge in order to create a source of water for the Althingi.Öxarárfoss can be reached by a short hike along Almannagjá gorge either from the park (the waterfall is not too far from the Silfra fissure itself), or from a path that can be reached from a turnoff from Þingvallavegur road. For fans of the TV series 'Game of Thrones', this path is also the way into the inpregnable Eyrie!
Silfra Fissure was formed within the divergent tectonic boundary between the North American and Eurasian plates. This 'fissure zone' runs across the middle of Iceland and makes up a small portion of the Mid-Atlantic Ridge. The Mid-Atlantic Ridge, on the other hand, runs from the Mid-Arctic Ridge, which is located northeast of Greenland, right through the Atlantic Ocean until it meets the Antarctic Plate. This not only makes Iceland one of the few places in the world (including Jan Mayen, the Azores and Tristan da Cunha) where volcanoes on the Mid-Atlantic Ridge are visible above sea level, but also the only place in the world where the axis of the ridge can actually be observed.The Silfra Fissure, although located inside a large rift valley, lies much closer to the west edge of this valley--the edge marked by the 7.7 kilometre-long Almannagjá gorge. The eastern edge of the valley, in turn, is marked by the Heiðagjá gorge. When the tension that builds up over decades is released and causes the plates to split apart, the rift valley ends up sinking between these two gorges--sinking valleys like this are known as 'grabens'. During the earthquakes that struck the area in 1789, the valley floor of Þingvellir sank by almost two metres.This slow remodelling of the land creates all sorts of cracks and fissures, but what makes Silfra unique is that when it was created, an underwater spring was cracked open in the process, and it flooded the fissure with crystal clear water. From the surface, this narrow channel of water really does not look like much, but when you are diving inside it, in-between two tectonic plates, and when the enormous geological power that is slowly splitting the land apart dawns on you, the experience becomes incredibly surreal.
One thing that immediately strikes divers is the unbelievable visibility of Silfra Fissure, which can be in excess of a hundred metres. The water is so clear, in fact, that I found the reflections of the rocks on the surface of the water to be somewhat disorientating. The water originates from the Langjökull glacier , which lies more than 50 kilometres away from Þingvellir National Park. Approximately 12,000 years ago, the glacial meltwater flowed unimpeded via rivers directly to Lake Thingvalla, but the eruptions that created the Skjáldbreiður volcano also created a lave field that covered more than 300 km2 and blanketed the river, essentially forcing the water underground to form an aquifer. Volcanic rocks, especially vesicular rocks such as scoria, are porous, and they act as filters that trap particulates within the glacial water. The journey through these rocks, that supposedly takes between 30 and 100 years, not only ensures that the water that emerges is incredibly clear and pristine, but, due to the high mineral content, also refreshingly potable.
The dive begins with a short walk from the carpark towards the stairwell that descends into the Silfra Fissure. Just behind the stairwell is a hole of sorts that is referred to as the 'toilet bowl'. The reason for this is because the hole links to a small tunnel that is approximately 16 metres deep, that the water from the underground spring travels through on its way into the fissure. The tunnel was also used in the past to 'flush' scuba divers, hence the name, into the fissure itself using the pressure of the water that is generated by the narrow opening. This is now rarely done, however, as the stability of the tunnel is supposedly compromised. There are also networks of cave passages behind the tunnel towards the direction of the carpark, but they are not accessible to recreational divers.Once divers descend the stairwell, they enter the first section of the Silfra Fissure that is known as the 'Big Crack'. This section is more than a hundred metres long and its deepest section reaches 45 metres. The depths of this section cannot be explored even though you may be certified to dive that deep, as Icelandic regulation does not permit divers to dive below the 18-metre open water recreational limit. Not only does this section contain the deepest parts of the fissure, but it also contains the narrowest as well as the shallowest. Divers usually stop at the narrowest part to take pictures as they are able to touch both sides of the fissure at the same time to give the impression that they are pushing the continental plates apart. The shallowest parts also end up making the dive a multi-level dive as divers have to shallow up multiple times to pass through three 'islands' that are only about 0.5 metres deep.