Eldur úr Jörðinni: the Why and How of Iceland’s Volcanoes
Note: Dr. Lozoz will present a talk on Icelandic Volcanism during a free online public webinar on Friday, November 20, 2026. Details on our event calendar.
By Dr. Julian C. Lozos, Associate Professor of Geophysics, California State University,
Northridge
Iceland is classically referred to as the Land of Fire and Ice. The Ice has not always
been a big part of the landscape; its presence now is largely an effect of latitude. But
the Land itself, which that ice occupies, has a far more unusual origin that ties into a
very specific set of circumstances with the Fire.
The birth of Iceland as a landmass is extremely recent from a geological standpoint
(around 17 million years ago), both as a result of and an unusual case within plate
tectonics. To briefly take you back to Geology 101: the theory of plate tectonics states
that the outermost layer of the Earth is broken into large rigid chunks that drift around on more pliable rock deeper inside the planet. At the edges of these slabs of rock, where
they move toward, away from, or past each other, the forces of that interaction can be
intense and violent, leading to the formation of mountains, to earthquakes, and to
volcanoes. At one point, Europe and Africa were attached to the Americas, but a crack
between them slowly expanded and moved them apart, all the while the Atlantic grew
larger. The Atlantic is, in fact, still expanding, as new ocean floor forms by erupting out
of the 16,000-kilometer-long volcano that runs north to south through its center, called
the Mid-Atlantic Ridge.
This type of spreading is textbook plate tectonics. Mid-ocean ridges, by definition, make
ocean floor. But Iceland, above sea level, also sits atop the Mid-Atlantic Ridge, also
growing at the rate that the Atlantic Ocean spreads. This would not be able to happen
under normal conditions, however. This land only exists because of a hot spot (heitir
reitir á íslensku) – a superheated plume of molten rock shooting upward from the edge
of the Earth’s core and burning through to the crust like a geological flamethrower –
situated right under the Mid-Atlantic Ridge. The extra molten rock from the hot spot,
plus the easy way out as North America and Europe move further apart, allowed
enough material to pile up to build an island where there would otherwise only be ocean floor. On the modern Earth, Iceland is the only place with this exact coincidence of forces.
Iceland is land and not ocean, but its rocks and their behavior still have more in
common with the ocean than with continents. The black rock that makes up most of the
island, basalt, is the same stuff that makes up the ocean floor. This is a dense, metal-
rich rock that is very runny when in its liquid form. Under water, it spurts out of long,
narrow cracks that parallel the mid-ocean ridge, then it cools nearly instantly upon
meeting cold water. On land, those same fissures rupture the surface and into the air, as
we have seen so many times on the Reykjanes Peninsula over the last few years. The
chemical properties of that ocean-floor lava are responsible for the glowingly energetic
fountaining and flowing that make these eruptions as much of an attraction as they are
a hazard. These curtains of fire are so characteristic of Iceland that even when they
happen somewhere else on Earth, they are still called “Icelandic-style eruptions.”
But when the ice meets the fire, a volcano’s behavior can change. Heat a glacier and
you get meltwater; put water into a volcano, and it turns to steam. Steam is a volatile gas that rises and expands in its own right, and can also escalate a more effusive eruption into a more explosive one. The infamous 2010 eruption of Eyjafjallajökull was one such case. This was not a large eruption from an amount-of-lava standpoint, nor was the lava sticky and viscous enough that only an explosion could clear it from the plumbing system within the mountain. It was just the confluence of heat, steam, and the current wind conditions that allowed this eruption to freeze up air travel across Europe. But there are bigger volcanoes with more voluminous magma sources in Iceland, many also capped with glaciers; the same kinds of conditions that influenced Eyjafjallajökull, but acting on a larger scale, could lead to more widespread, longer-lasting, and severe consequences.
Just as volcanism has shaped the landmass of Iceland, just as nobody could possibly
have had Icelandic roots if this extremely particular strange tectonic configuration had
not made land where there would normally just be ocean, lava and ash have continued
to have a say in who remains on the island. The 1362 eruption of Öræfajökull, with its
explosions, ashfall, and flooding from rapid glacial melt, drove those whom it did not kill
outright away from the Skaftafell area for more than 40 years. The 1780s saw ashfall
and glacial melt flooding from Hekla, Katla, and Öræfajökull again, but those damages
to farmland were still relatively minor when compared to the 1783-4 fissure eruption at
Laki, which spewed so much toxic gas in the air that the resulting losses of life due to
immediate poisoning or growing famine extended well beyond Iceland, into mainland
Europe. The volcanoes made it clear that this could be inhospitable, outright hostile
land.
However, the human outcomes of a major eruption in 1875 were somewhat different
than just the survivors buckling down to weather the aftermath. Askja is a large volcano
with lava that is more viscous, and therefore requires more explosive force to clear it out
of the volcano, than the baseline Icelandic basalt, but its location in the eastern
Highlands buffered settlements further to the east from a directly fatal hit. But the
damage done against farmland and the many livelihoods tied to it was enough to fuel a
movement west, beyond the half of Iceland that plate tectonics carries east with Europe,
and onto continental North America. By this time, word of encouragement from
Scandinavian immigrants to the United States ' Upper Midwest, as well as formal
government efforts to bring Icelanders to the prairies of Canada, had already started a
wave of immigration. The 1875 Askja eruption only served to dramatically accelerate
that movement. The winters in this area proved to be harsher than what people were
used to in Iceland, and the new settlements still had to grapple with difficult fishing and
farming, and with waves of disease. But because the North American prairies are
central on the oldest part of the continent, far from the influence of any other tectonic
plates, there was, at least, absolutely no risk of volcanism here.
