Investigating long-period and ultra-long-period oscillations in magma density of the current Cumbre Vieja eruption on La Palma (Canary Islands, Spain)

Volcanic eruptions in the Canary Islands are rare events. They occur on average every few couple of decades to centuries.

In mid-September 20 21 and eruption started on La Palma after a 50 year hiatus in eruptive activity on the island. It has now become clear that this eruption is the largest eruption on La Palma in several thousands of years and probably among the largest eruptions in the archipelago in several thousands of years.

The eruption started out as a fissure eruption feeding magma to form several lava flows. At the end of October the eruption style changed drastically turning increasingly explosive with the advent of giant lava fountains reaching heights in excess of 600 m above the event.

This change in activity requires drastic changes in magma density as magma rises from depth to erupt at the surface. We suspect a reduction in density by a factor of 2 to 3. However, there is currently no instrumentation on La Palma which can shed light on these density changes. This project aims at quantifying magma density changes by installing a network of three gravimeters: geophysical instruments that are sensitive to density changes at depth. The gravimeters will be strategically installed atop of magma reservoirs that we now know are connected between 35 km and around 5 km depth to feed the current eruption. Based on preliminary findings from project partners, the plumbing system of the eruption is geometrically complex and requires substantial lateral flow of magma from an intermediate-level magma storage at around 10 km depth to the most shallow storage at around 5 km depth. There is now the opportunity to study the drastic variations in density along the path of magma in unprecedented detail. Theoretical models of magma replenishment indicate variations in physical properties of magma such as density over periods of hours to weeks. The eruption on La Palma provides us with hence an unprecedented and unique opportunity to test these theories. We will be able to quantify not only the variations in magma density but also its evolution in time and space using advanced numerical models and data interrogation tools. Furthermore we can link our findings with the dynamics of the eruption that is captured by publicly available video footage to study the relationship between magma density changes and eruptive activity.

This will afford us with new insights into processes within the plumbing system of the current eruption in La Palma and also more broadly for similar eruptions elsewhere in the archipelago and other volcanic ocean islands. Ultimately, there is scope in project to evaluate the benefit of gravimetric networks to aid eruption forecasting and hazard assessment.