A new chapter in volcanic activity on the Reykjanes Peninsula

Haraldur Sigurðsson, volcanologist and professor emeritus at the University of Rhode Island, says a new phase of volcanic activity began on April 1 in the Sundhnúkur volcanic system. This chapter, he believes, is likely to be marked by renewed magma flow beneath the surface.

In a social media post, Sigurðsson reflects on the current situation in light of a recent scientific article by Michelle Parks and 20 co-authors. While praising the study for offering a strong overview of the Sundhnúkur system's activity, he also notes its limitations.

“The interpretation doesn’t go deep enough—only down to about four kilometers,” he writes. “To truly understand what’s happening, we need to look deeper into the Earth’s crust and the underlying mantle.”

Three distinct phases

Sigurðsson outlines three distinct phases that, in his view, characterize the ongoing activity in the region:

1. November 2023 to April 2024
   During this period, six eruptions occurred in rapid succession, with magma inflow into the system steadily declining—from 7.6 cubic meters per second down to 4. This downward trend formed the basis for a prediction by geophysicist Grímur Björnsson that the eruption series would end by summer or autumn 2024. “But the trend shifted, and the prediction no longer held,” Sigurðsson notes.
2. April 2024 to March 2025
   This second phase was characterized by pauses of roughly three months between eruptions, and a continued decline in magma inflow—from 4 cubic meters per second to just 2.5.
3. April 2025 to Present
   Marked by large-scale crustal movement and tectonic shifts, this latest phase may once again lead to increased magma activity.

“The unifying factor throughout all three periods is the steadily decreasing magma inflow into the chamber beneath Svartsengi, at a depth of about four kilometers,” he writes.

Magma flow has dropped by two-thirds

Since November 2023, magma flow from the mantle has dropped by nearly two-thirds—from 7.6 to 2.5 cubic meters per second. The rate at which magma is produced in the mantle and rises toward the magma chamber is key to understanding these changes.

According to InSAR satellite data, the magma chamber forms a flat cone beneath the surface, centered just south of the Blue Lagoon and west of Mt. Þorbjörn. It may span up to 10 kilometers in diameter. The land directly above this chamber has risen by as much as 40 centimeters.

More than just lava and eruptions

While the public often focuses on lava and visible eruptions, Sigurðsson argues that the most important processes are happening deep below. The major tectonic event that occurred on April 1—likely due to significant plate movements and crustal shifting—could make it easier for magma to rise from the mantle.

“Land uplift resumed immediately after the last eruption, potentially at a faster rate than before,” he says. “The question is whether the tectonic shift has facilitated magma movement into the Svartsengi system.”

A call for deeper research

To answer these questions, Sigurðsson advocates for deeper geophysical investigations of the region. He points to seismic imaging from research vessels as a promising method. These ships send powerful sound waves through the crust and mantle, producing high-resolution images of what lies below.

Sigurðsson says his colleague, Professor Yang Shen at the University of Rhode Island, is currently seeking funding for such an expedition around the Reykjanes Peninsula.

“To fully understand what’s happening here, we must go deeper—beyond four kilometers—into the Earth’s mantle,” Sigurðsson concludes. “Only then can we grasp the full story of this remarkable volcanic system.”