Much Ado About Earthquakes: Understanding the Eldey and Reykjanes Volcanic Systems

Two volcanic systems, both alike in dignity, in fair southwest Iceland, where we set our scene. But what’s in a name, and why do these two volcanic systems keep getting confused in the social and news media?

To erupt, or not to erupt: that is the question at the Svartsengi volcanic system, which is currently awaiting a potential tenth eruption in two and a half years as magma accumulation reaches 30 million m3 (equivalent to 30 billion litres!) below the world-famous Blue Lagoon. But if you have been watching Iceland's earthquake maps lately, you may have noticed that there’s been a lot of seismic activity offshore now, around the western tip of the Reykjanes Peninsula and out along the Reykjanes Ridge.

And if you have been following the headlines, vlogs, or social media updates, you may also have seen these earthquakes described as happening “at Eldey,” “on Reykjanes,” or simply “near the Reykjanes Peninsula.” These may sound geographically interchangeable; but geologically, they are not!

How connected is the Eldey volcanic system to neighboring systems?

Iceland's Reykjanes Peninsula and offshore ridge extension contains several separate volcanic systems, each with its own fissure swarms, eruptive history and shallow plumbing system (although many of these systems may be connected at a deeper level, but this is a discussion for another article). The Eldey volcanic system and the Reykjanes volcanic system are two of them.

They are neighbours. They are both basaltic. They both sit on the same tectonic plate boundary. And both extend or are located wholly offshore. But they are not the same volcanic system, and that distinction becomes particularly important when we try to interpret earthquake swarms and ask the question everyone really wants answered: is magma moving, and could an eruption be coming?

The short answer is that some evidence points in that direction, some evidence is clearly not volcanically linked. The longer answer is much more interesting and complicated, like most things in geology. Let’s explore these two volcanic systems, the plate margin they sit on, and the seismic unrest we have been seeing over the past few years now.

Map of southwest Iceland showing the volcanic systems of the Reykjanes Peninsula shaded in pink and the offshore Eldey system outlined in pink.

Map of the volcanic systems of the Reykjanes Peninsula, as well as the offshore system of Eldey in a pink outline.

The Reykjanes Ridge: the through-line that ties Iceland’s southwest volcanic systems together

The Reykjanes Ridge is the submarine expression of the Mid-Atlantic Ridge (MAR) in southwest Iceland, i.e. a section of the global mid-ocean ridge system where the North American and Eurasian plates are pulling apart. As the ridge approaches Iceland, it rises toward the surface and eventually comes ashore at the Reykjanes Peninsula, making the peninsula essentially the land-based continuation of an oceanic spreading ridge. But the transition isn't quite as simple as a line continuing neatly from sea to land. Offshore, the Reykjanes Ridge is dominated by extension and seafloor spreading; on the peninsula, the plate boundary becomes more oblique, producing a combination of extensional normal faulting and strike-slip motion. This complex geometry has created a series of elongated volcanic systems and fissure swarms stretching across the peninsula, while offshore the volcanic activity mirrors typical Mid-Atlantic Ridge geologic architecture.

It is key to note that this ridge can see a lot of seismic activity that is purely tectonic in nature as the two major plates spread apart from one another, and many of the earthquakes along this ridge have no direct ties to magma movement or volcano formation.

The Reykjanes Peninsula Volcanic Systems: a new era of volcanism in the region

If you have been following Iceland volcano news, you know that the Reykjanes Peninsula has entered into a new, active phase of eruptive activity, with twelve eruptions between two volcanic systems in the past five years. The volcanic systems along the peninsula all seem to be genetically linked deep within the earth’s crust, erupting in cycles together of dense activity for 100-200 years followed by 800-1000 years of quiescence. With the eruptions at Fagradalsfjall followed by Svartsengi, it is clear we have entered into a new chapter of active volcanism.

The big question is: which system will erupt next and when?

There has been a flurry of seismic activity at almost all the other systems of the Reykjanes Peninsula, but it can be daunting to distinguish between magmatic and tectonic movement within the crust when analyzing just a single earthquake. Geoscientists need multiple data points over a period of time to be able to propose trends and assign hypotheses to the seismicity they see.

Two such seismically active areas along the Reykjanes Ridge and Peninsula are neighbors Reykjanes Volcanic System and Eldey Volcanic System.

The Reykjanes Volcanic System

The Reykjanes volcanic system is the westernmost volcanic system on the peninsula. It has no central volcano. Instead, it consists primarily of fissure swarms that trend roughly southwest–northeast, with both onshore and offshore portions. The lavas of this system build out southwestern tip of the peninsula into the ocean, and many lava flows have been lost to the waves either through erosion or subaqueous deposition.

Its fissures have produced lava flows, crater rows, scoria cones and tuff cones, while offshore eruptions have left tephra layers that can be identified in soils on land. At least 15 tephra layers have been associated with eruptions from the offshore part of the Reykjanes system.

These were not one single eruption; this is an important decision. When local volcanologists say that the Reykjanes system “last erupted 800 years ago,” it is tempting to imagine a volcano that erupted once in 1210 and then switched off. That is not what the geological record suggests.

The Reykjanes system, along with its counterpart systems along the peninsula, appear capable of entering periods of repeated eruptive activity with multiple eruptions per active episode.

The Eldey Volcanic System

The Eldey volcanic system lies on the northernmost Reykjanes Ridge, southwest of the Reykjanes Peninsula offshore. Unlike the largely land-based systems farther east along the peninsula, Eldey is overwhelmingly submarine. The system includes Eldey Island and several smaller skerries, but most of its volcanic landscape is hidden beneath the ocean.

That makes Eldey fascinating… and frustrating.

Eldey is a submarine fissure-vent system whose characteristic activity is explosive submarine basaltic eruptions. Six small eruptions have been identified within the system during approximately the last 1,100 years, with the most recent in 1926.

Historical records suggest eruptions or suspected eruptions around Eldey in 1211, 1340, 1422, 1879, 1884 and 1926, although some of those events are considerably better documented than others and some historical locations are uncertain. Several produced temporary islands that were subsequently destroyed by the waters of the North Atlantic.

That is one of the defining characteristics of Eldey: scientists know it erupts, and know it has erupted much more frequently than its neighbors in modern times, but because the system is fully underwater means nobody can directly see what is happening.

Most of the system is deeply submerged, and its eruptions can be short-lived and difficult to observe directly. The geological record is therefore much less complete than it is for a system such as Reykjanes, where lava flows and crater rows are sitting on land waiting for geologists to map them.

Geochemically speaking, the lavas appear to have more in common with Mid-Ocean Ridge Basalts (MORB) than volcanic systems of the peninsula. The island is largely composed of volcanic tuff produced by explosive interaction between magma and seawater, also. And because so much of the system lies offshore, knowledge of its past behaviour is inevitably patchier. But given its eruptive history and trends, its geochemistry, and geography, the prevailing hypothesis is that the Eldey volcanic system is not linked to the volcanic systems on Reykjanes.

What does the offshore seismic unrest tell geologists about upcoming volcanic eruptions?

The recent earthquake swarms must mean one of these volcanic systems is about to erupt, right? Wrong. Interestingly, there are different types of seismic activity happening directly offshore of the Reykjanes Peninsula and each type could indicate something different:

Map showing dense, colour-coded earthquake swarms along the Reykjanes Ridge and western Reykjanes Peninsula, with the largest clusters offshore near Eldey and southwest of Reykjanes.

All earthquakes in the region from 01 January 2026 through 22 August 2026. Swarm Type One is typified by quakes in red; Swarm Type Two can be represented by quakes in blue and yellow; and Swarm Type Three is similar to the light green quakes (sitting under the red colored data).

Swarm Type One: Small earthquake swarms that happen semi-regularly and semi-linearally, mainly NNE-SSW trending, concurrently with small swarms to the west of the Kleifarvatn, just off of Reykjanesta, and at a depth of a few kilometers. These have been happening since inflation at Svartsengi began, sometime in 2020-2021. What this could possibly be: as the earth is being pushed up by magma at 4-5 km depth above Svartsengi (called inflation), this can cause the crust to bend and flex at the edges of curvature. These are sometimes referred to as trigger earthquakes.
Swarm Type Two: Moderate earthquake swarms that happen every few months forming a vertical line or sheet geometry in the subsurface, spanning deep to semi-shallow, close to Eldey island. These have been happening for about two-three years from 2024 onward. What this could possibly be: this could be normal tectonic movement along the Reykjanes Ridge, but it also could be magma movement at the Eldey volcanic system. Scientists would look for other data types that would corroborate the magma movement hypothesis, but this is hard since this volcanic system is entirely submarine and thus data collection is difficult.
Swarm Type Three: Moderate earthquake swarms that happen every few months forming a vertical line or sheet geometry in the subsurface, spanning deep to semi-shallow, close to Reykjanesta. These have been happening for about two years from 2024 onward. What this could possibly be: this could be normal tectonic movement along the Reykjanes Ridge, and could also be trigger quakes, but it could be magma movement at the Reykjanes volcanic system. Scientists would look for other data types that would corroborate the magma movement hypothesis, and so far no inflation is seen on GPS or satellite data.

To summarize, many of the earthquakes we see are normal Mid-Ocean Ridge tectonic movement and/or trigger quakes. However, we now see swarms at various depths surrounding Eldey island and just off the tip of the Reykjanes Peninsula (called Reykjanesta) that look similar to magma movement swarms as seen at other volcanic systems on Reykjanes. Without further data to corroborate a magma movement hypothesis, we cannot say with confidence that this a sign of magma movement at the Reykjanes and/or Eldey volcanic systems.

To add data to which volcanic system might be experiencing unrest, Reykjanes or Eldey (or both), the current research and past eruption records present several ideas.

Prevailing theories about the genetically linked volcanic systems of the Reykjanes Peninsula

These theories say that each system erupts separately and discretely, and that other systems will not erupt while one is erupting; that said, this does not preclude one system from gathering magma while another is active. Both Fagradalsfjall and Svartsengi systems were “charging” simultaneously, they just erupted at different times. This could mean that Reykjanes volcanic system could be starting to gather magma in the subsurface to erupt eventually, but with Svartsengi still potentially active, that adds doubt to Reykjanes erupting soon.

The volcanic system of Eldey has erupted on a very different schedule than the Reykjanes Peninsula systems, including four confirmed and/or suspected eruptions in the past 150 years. So the Eldey system is marching to the beat of its own drum and not tied to the possible constraints exhibited by the systems along Reykjanes. Thus an eruption there could occur while activity is ongoing at Svartsengi volcanic system, or even Reykjanes volcanic system.

So, will we see a new eruption at Eldey anytime soon?

The fault (pun intended) is not in our volcanoes, but in our data. A volcano will erupt when it chooses; sometimes there will be eruption trends to help us predict, sometimes not. But unfortunately in submarine systems where data collection is difficult and patchy, and data collection has only been occurring at modern, high-tech levels for a few decades only, scientists simply do not have enough data to make confident predictions in some areas. Unfortunately this is most likely a “wait and see” situation with both volcanic systems, as scientists will collect more data, build more analog trends, and continue to build hypotheses as to what will happen next.

Experience Real Molten Lava

The earthquake swarms around Reykjanes and Eldey reveal how active and complex Iceland’s plate boundary can be—but seismic activity does not always mean that magma is moving or an eruption is imminent. At Lava Show, you can safely witness what happens when magma reaches the surface and becomes lava. Feel the intense heat of real molten lava, hear it crackle as it cools and watch it solidify just metres away.

Plan your visit:

Experience Lava Show Reykjavík – Watch real molten lava flow in Iceland’s capital.
Experience Lava Show Vík – Experience the world’s only live lava show on Iceland’s South Coast.