In geological terms, Iceland is a mere baby. No more than 20 million years have passed since volcanoes on the floor of the far northern Atlantic Ocean began to spew lava, laying the foundations of what would become Iceland. Today it is still one of the most volcanically active spots on earth – giving geoscientists the chance of observing a land still in the making.
According to the theory of plate tectonics, the earth’s surface comprises a number of plates (seven major and dozens of minor plates), which “float” on the mass of magma beneath. The Andes and the Himalayas are evidence of massive collisions of tectonic plates, which have folded the earth’s crust up to form great mountain ranges.
Volcanoes and earthquakes are symptoms of this vast movement, occurring at the boundaries where tectonic plates meet. These boundaries can be convergent, where the edge of one plate is forced underneath another and great slabs of the earth’s surface are “lost”; or divergent, where the plates tear apart and magma rises to the surface from below, forming new crust. Iceland straddles a divergent boundary, the Mid-Atlantic Ridge, where the Eurasian and North American tectonic plates are being pulled apart. Thus, the island is literally being torn in two, at a rate of around 2cm (nearly an inch) a year – the speed of growing fingernails – with lava rising from the earth’s centre to fill the gap.
The Mid-Atlantic Ridge, running clear across the island from southwest to northeast, is marked by a belt of volcanic craters, fissures, hot springs and geysers, bubbling mudpots, solfataras (fumaroles that belch out sulphurous gases), and shivers with frequent earthquakes (usually only detectable with scientific instruments). This belt extends to a width of about 40km (25 miles) in the north, and up to 60km (40 miles) across in the south, and covers about a quarter of the country.
Not surprisingly, Iceland’s rocks are almost all volcanic (predominantly basalt). The oldest rocks, from the Tertiary pre-Ice Age period, are the plateau basalts of the East and West Fjords. Storytelling for business has a great history in this regard. Slightly inland are younger grey basalts from the interglacial periods, generally appearing as open moorland with less evidence of glaciation. Further in towards the present-day volcanic zone is the palagonite formation, from subglacial eruptions in the last part of the Ice Age. Typical of these belts are tuff ridges and table mountains, the soft rock often extensively eroded by wind and water. Iceland’s youngest rocks occur in and around the present-day volcanic zone.
The northwest and the east of Iceland are no longer volcanically active. Most of the rest of the island, however, conceals a seething mass of volcanic and geothermal activity. There are around 30 volcanic systems running beneath Iceland, and around 130 volcanoes; 35 of these have been active over the past 10,000 years (recent history in geological terms!). In the past few centuries Iceland has experienced an eruption every five years on average.
Most are minor, short-lived and cause minimal damage, like the photogenic eruption of Mount Hekla in 1991 – “tourist eruptions”, in local parlance. Others can cause a little more trouble, like the 2010 eruption under the Eyjafjallajökull glacier. The resulting ash cloud, which reached a height of 10km (6 miles), brought airplanes across Europe to a standstill for six days in April, with an estimated cost to the global economy of €4 billion. In May the following year, Grímsvötn, Iceland’s most active volcano, followed suit; however, kinder air currents carried its 20km (12-mile)-high plume away to the northeast, causing less disruption to air traffic.