[Rockhounds] Iceland Volcano Leads Geologists to New Lava Fountain Theory

[Kreigh Tomaszewski]

A past eruption of Iceland's Fagradalsfjall volcano has led scientists to a
new theory on why and how volcanic fountains form.

An international team of scientists studied a 2021 eruption of the
Icelandic volcano to reach their findings, which have been published in the
journal *Nature Communications.
<https://www.nature.com/articles/s41467-023-42569-9>*

While studying the spectacular lava fountains of Fagradalsfjall, the
scientists theorized that these types of low-lying volcanoes have a shallow
cavity filled with magma beneath the caldera. They believe that, as the
magma rises, a layer of foam accumulated by gas forms. A collapse of this
layer creates pressure that then pushes the magma out of the cavity and
into the air—creating the captivating lava fountains that we see.

https://www.newsweek.com/iceland-volcano-geologists-lava-fountain-theory-1847045


Lava fountains are a common manifestation of basaltic volcanism. While
magma degassing plays a clear key role in their generation, the controls on
their duration and intermittency are only partially understood, not least
due to the challenges of measuring the most abundant gases, H2O and CO2.
The 2021 Fagradalsfjall eruption in Iceland included a six-week episode of
uncommonly periodic lava fountaining, featuring ~ 100–400 m high fountains
lasting a few minutes followed by repose intervals of comparable duration.
Exceptional conditions on 5 May 2021 permitted close-range (~300 m), highly
time-resolved (every ~ 2 s) spectroscopic measurement of emitted gases
during 16 fountain-repose cycles. The observed proportions of major and
minor gas molecular species (including H2O, CO2, SO2, HCl, HF and CO)
reveal a stage of CO2 degassing in the upper crust during magma ascent,
followed by further gas-liquid separation at very shallow depths (~100 m).
We explain the pulsatory lava fountaining as the result of pressure cycles
within a shallow magma-filled cavity. The degassing at Fagradalsfjall and
our explanatory model throw light on the wide spectrum of terrestrial lava
fountaining and the subsurface cavities associated with basaltic vents.

https://www.nature.com/articles/s41467-023-42569-9