The Canary Island of La Palma has taken 50 years to host a new eruption. Since September 11, La Palma has been in the news for the numerous earthquakes and deformation that the National Geographic Institute has recorded in its volcanic surveillance network. Finally, the magma reached the surface yesterday, Sunday, September 19. What does it mean in geological terms what is happening?
A complex journey: the rise of magma to the surface
Active volcanic areas, such as the Canary Islands, bring magma from the depth to the surface. But this is only the end of the story.
Under the volcano, the magma accumulates in the form of reservoirs, and is transported through conduits, or dikes, as if they were the arteries of the volcano. The trip abroad is not easy or predictable, but we have the help of seismicity and deformation as precursor signs of eruptions.
Molten magma or rock “breaks through” by breaking the surrounding rock. This fracturing produces waves that are measured on the surface using seismometers, and can be felt by the population as earthquakes.
On La Palma, the seismic swarm at the beginning of last week came from depths of about 12 km, reflecting the accumulation of magma in reservoirs at the base of the earth’s crust, around the critical point that can lead to an eruption. Although this seismicity began in 2017, its intensity has increased in recent days, and has been felt by the population. In addition, the progressive rise of the magma has been generating shallower earthquakes.
Taking into account the seismicity recorded on La Palma, it could be said that there have been at least 5500 rock fractures in recent days. Finally, the beginning of the eruption generated the largest earthquake, when the feeder dam completed its journey breaking the rocks on the surface, generating the eruptive fissure, which has several emission centers or eruptive mouths.
In addition to fracturing the rocks, magma accumulates in areas of the crust where it finds “holes”. This accumulation causes the magma to “push” the materials that are still above it, which is expressed on the surface as a bulge or deformation, which in the Palm has been approximately 10 cm.
Oceanic volcanic islands: the tip of the iceberg of large volcanic buildings
Oceanic volcanic islands such as the Canaries represent the emerged part of large volcanic buildings. La Palma, for example, is just over 2400 meters high, however, under the sea it continues to be about 3000 meters higher. In other words, the island is the tip of the iceberg of that great volcano that is more than 5 km high.
This means that most eruptions occur under the sea, like the last one on El Hierro. In the case of La Palma, the eruption is occurring in insular territory, like the seven eruptions of the last 600 years on the island. The current eruption is located in an area with a large number of emission centers and fissures from past eruptions, which shows the importance of our study of the geological past to understand its present and future.
The danger of eruptions
We live on an active planet that has been in operation for 4.5 billion years. The increase in world population has led to the occupation of geologically active areas, such as the fertile volcanic lands of the Canary Islands. All geological processes, including volcanic ones, imply a “danger”.
If these processes generate economic losses, human lives or productive capacity, then they also imply a “risk”.
Faced with the event of the eruption on La Palma, the Canary Islands Government activated the Canary Islands Volcanic Emergency Plan PEVOLCA. The alert situation is established qualitatively with a traffic light that changes from green to yellow, to orange, to red as the probability of an imminent eruption increases.
At this time, the traffic light is red, which indicates that the evacuation of the population that may be affected must be carried out as an active measure of Civil Protection. The development of the new eruption is associated with the emission of lavas and falling pyroclasts, which are fragments of magma separated and cooled during the eruption, due to their explosive nature.
The last eruption of La Palma in 1971 gave rise to the Teneguía volcano and generated not only the growth of the island, since the lavas gained ground from the sea, but also a great expectation and an advance in the scientific knowledge of the eruptions in the archipelago .
These days we are witnessing that most of the Canary Islands are volcanically “alive”, and will continue to produce eruptions in the future.
Laura Becerril, Geologist, volcanologist. Assistant Professor, University of O’Higgins (Chile); Carlos Galé, Geology, University of Zaragoza; Patricia Larrea, Assistant Professor, Geology Department, Universidad de Chile and Teresa Ubide, Senior Lecturer in Igneous Petrology / Volcanology, The University of Queensland
This article was originally published on The Conversation. Read the original.
