Student Reports

Written by Megan Campbell, Becca Tanner, Charlie Jackson and Rebeka Bacova

Abstract

A microseismic survey was conducted at the Cuevas del Viento lava tube in the Icod valley in Northern Tenerife. The survey was implemented by Group A GeoInterns 2022 who designed the experimental layout and procedure. The survey was conducted over two days to explore whether microseismicity can be a useful tool in identifying shallow subsurface features, such as lava tubes, which are abundant in the Icod valley. The results were obtained and processed by Pablo Gonzalez a local scientist overseeing out survey and we analysed the possible results. The results sound small anomalies across the transect but not anything of extreme significance. A similar study of lava tubes at Mt Etna (Muniruzzaman, 1978) found small peaks at similar values so we hypothesise that we detected the topsoil layer rather than any notable subsurface feature. In future, longer time should be spent both completing the survey and in collection time, to see if this yield more significant results.

Background

A microseismic survey consists of applying passive seismological techniques to image the interior of the Earth. Acoustic waves are naturally occurring and are continuously generated by different motions, such as earthquakes and vibrations. There are 4 different types of acoustic waves: P-waves, S-waves, body waves and surface waves, and these all exhibit their own properties which distinguish them from each other and can be used in different ways to image the planet.
S-waves are used in this study and are a type of transverse wave where the particle motion moves parallel to the direction of motion. Geophones are used to detect these waves and work by employing the fundamental mass on a string principle for detection. This applies a mass on a spring which is sensitive enough to move when in contact with acoustic waves. This movement is detected and transformed into an electrical signal which can then be interpreted by the reader and the data can be used in processing. The signal received is recorded in three component directions: north, east and vertical, although other geophones record in two or four dimensions e.g. Brenguier et al. (2016).
Applications of passive seismology include seismic tomography studies which can image complete magmatic systems and further into the mantle. For example, a study by Gorbatikov (2013) used a seismic tomography study to image the plumbing system of El Hierro in the Canary Islands which found a deep seated 35km anomaly indicating that magma was localised in this region deep below the island.

Geological Setting

The survey was completed above the Cuevas del Vientos lava tube in Icod del lod Vinos, in Northern Tenerife. This area is situated north of Teide volcano and the Las Canadas caldera and has been inundated by many lava flows during the Holocene-Pleistocene. Thus far, the lava tube has been detected for up to 17km through previous surveys, but it is estimated that it could be as long as 75km. At its current measurements, it is the fifth longest lava tube in the world, and largest outside of Hawaii. The caves showcase unique geomorphologies due to the three distinct levels of tubes which are superimposed on one another. Other typical features of lava tubes can be found within the cave, such as lava stalactites, cascades, terraces and lakes. The cave, like other lava tubes on the island also hosts unique species of insects that are endemic to the caves.
A lava tube is formed through the natural lava cooling process. When the lava flows the outside of the lava is exposed to the elements, meaning it cools down more rapidly than the centre. The lava cools on the sides of the flow first, creating levee type structures. After long enough this builds up forming a roof, which allows the interior of the tube to start cool. Whilst this exterior shell has hardened the inside is still largely molten and continues to flow under the influence of gravity. This allows the tube-like shape to form as the inside will eventually become hollow forming the lava tube.
This study aims to investigate the role of micro seismic surveys and their use in identifying subsurface features like lava tubes, where in the Icod de los Vinos area, ~80% of the lava tubes remain undiscovered.

Methods

The microseismic survey was designed by 9 GeoInterns in the GeoTenerife internship and carried out on the 12th and 13th of September 2022.
The geophones were spaced 3m apart along transects perpendicular to the direction of the lava tubes, which was north. The Old Lady Skylight was used as a reference point as we had been in there to understand what we were trying to detect. The geophones were switched on and left for 45 minutes to record the ambient acoustic waves. After this time, the data was converted in the field by Dr. Pablo Gonzalez and able to be analysed immediately in the field. This set up was repeated along along the transect covering a total distance of ~45m. Upon starting a new measurement observations of the weather and local conditions were made to ensure we could refer back if the results contained obvious noise or something unexpected.
Geopsy software was used to process the data collected by the geophones. It created H/V (horizontal component/vertical component) plots against frequency detected. The peaks observed corresponded to the fundamental frequency, f0, of the layer being imaged.

Conclusion

A microseismic survey was conducted at the Cuevas del Viento lava tube in Northern Tenerife to try to justify the use of this method for identifying shallow subsurface features. The experiment was designed and conducted by 9 GeoInterns in September 2022 under the supervision of Dr Pablo Gonzalez. The results found that there was a small anomaly in a region of the transect infront of the Old Lady Sky light, however this was small and a physical conclusion of what the subsurface looked like was not reached. We suggest that in the future this method could be used to explore the shallow subsurface but time should be spent re-designing the experimental procedure and set-up.

References

Brenguier, F., Kowalski, P., Ackerley, N., Nakata, N., Boué, P., Campillo, M., Larose, E., Rambaud, S., Pequegnat, C., Lecocq, T. and Roux, P., 2016. Toward 4D noise-based seismic probing of volcanoes: Perspectives from a large-N experiment on Piton de la Fournaise Volcano. Seismological Research Letters, 87(1), pp.15-25.
Gorbatikov, A.V., Montesinos, F.G., Arnoso, J., Stepanova, M.Y., Benavent, M. and Tsukanov, A.A., 2013. New features in the subsurface structure model of El Hierro Island (Canaries) from low-frequency microseismic sounding: An insight into the 2011 seismo-volcanic crisis. Surveys in Geophysics, 34(4), pp.463-489.
Muniruzzaman, M., 1978. Microearthquake and background seismic noise studies of Mount Etna, Sicily.

Written by Federico Pingitore, Gregor Melville, Kez Page, Louis-Alexandre Lobanov and Molly Maenner

Introduction

During the third week of the GeoIntern Scheme, the nine students of Group A developed their fieldwork skills and undertook active research with Dr Richard Brown of Durham University, to further the project begun by the Interns the year before – “Closing the gaps in Las Cañadas eruptive history”. The overall aim of this research is to identify and categorise the gaps in the onshore eruptive history of the ancient Las Cañadas caldera. The caldera has been responsible for around 40 probable Plinian eruptions in the past 1.8 Ma, with ~18 of these being associated with widespread pyroclastic density currents. The apparent average timeframe of each eruptive event appears to be around 40 Ka.

Compared to a consistent stratigraphic history of explosive eruptions demonstrated by the marine records, surface records erroneously contain large gaps between known eruptions of the ancient volcano over the past 1.6 Ma. Furthermore, the larger and more interesting eruption deposits have experienced a selection bias within the Geological record in comparison to their smaller counterparts. By identifying these gaps, Dr Brown aims to determine the frequency and true number of Plinian and sub-Plinian eruptions on the island, as well as the likelihood of Tenerife experiencing an eruption of this scale in the future.

Methodology

For each of the five days of fieldwork from the 5th to the 9th of September 2022, we set out to visit outcrops of pumice fall and ignimbrites in the Bandas Del Sur region of the island of Tenerife. This area of the island’s south was chosen for the study as it demonstrates the best preservation of deposits within the Granadilla and Guajara Formations, influenced by the island’s NE trade winds and the direction of dispersal. Once at the localities, we traversed outcrops on foot and recorded significant findings such as the spatial relationship to other horizons, the petrology of any lithic/glass fragments and key identification characteristics of the observed lithologies within our field notebooks. Of important note is the use of field names when discussing some of the identified layers. Field names are those given to each new pumice fall identified, usually based on a defining characteristic of the pumice or the locality it was first identified at. These will not be used in the final published research and are instead used for easy remembrance and correlation of layers between the various localities.

The grain sizes of the clasts within each outcrop were studied using hand lenses and measured and categorised using the University of Leicester grain size cards. Samples of each named and identified pumice fall horizon were collected using common garden hand tools such as hoes, trowels and forks to scrape away chunks of the matrix for closer study. Around 200 small mass samples were collected for each pumice horizon, with lithic clasts or obsidian fragments being collected separately from any layers which contained them. The pumice mass and lithic samples were then bagged and labelled in the field. Upon returning to GeoTenerife HQ, the pumice samples were washed and sorted into grain sizes, which separated any mixed lithics from the matrix. At the same time, the separate lithic fragments were sorted into their respective sizes and horizon of origin and photographed for reference. Field photographs and stratigraphic records were also taken to aid in the classification of the layers by defining their prominent characteristics. These samples will later be used by Dr Brown in glass chemistry and 40Ar/39Ar laboratory analyses, allowing for fingerprinting and dating of the fall deposits.

Conclusion

As this is still ongoing research, an overall conclusion cannot be made at this stage. However, over the week of work we did, we were able to build upon the work started last year and laid the foundations for the next set of Interns to continue where we left off. Given that 24 distinct eruption events have been identified so far, it can perhaps be assumed that the Las Cañadas volcano erupted more frequently than what was previously believed.

Written by Megan Pelly, Ella Richmond, and Lucy Benniston

Introduction

The Canary Islands are a group of volcanic ocean islands formed by intraplate volcanism (Anguita and Hernan, 2000). The islands are volcanically active and are classified within the top 20 countries/territories for proportional volcanic threat (Longpre & Felpeto, 2021). The 2021 La Palma eruption caused extensive damage to property and infrastructure making it the most destructive eruption in La Palma to date (Martí et al., 2022). With increasing population and tourism in the Canary Islands, the risks associated with these events are increasing (Longpre & Felpeto, 2021).  

Understanding the awareness and attitudes of the general public towards volcanic events can be of significant importance in developing effective disaster risk reduction and management plans (AlQahtany & Abubakar, 2020). This project aims to collect data on the public perception and attitudes towards volcanic hazards in the Canary Islands to help build resilience.

Methods

Preparation and Resistance to Volcanic Eruption surveys were prepared by Catalina Argüello-Gutiérrez of the Universidad Internacional de La Rioja, Spain as part of the research project: PREVIA (Preparation and Resistance to Eruptions of Volcanoes in Ibero-America). The surveys are voluntary and anonymous. 

Surveys were distributed by students and staff of GeoTenerife on the Islands of Tenerife and La Palma in the Canary Islands, Spain. On the Island of Tenerife surveys were distributed on the 31st of August in the town of Garachico and the town of Arona. On the Island of La Palma, surveys were distributed at multiple locations across the island between the 5th and 14th of September 2022. 

Surveys were distributed to residents of the Islands over the age of 18 at shops, bars and restaurants, as well as to people met at GeoTenerife events and excursions. The principles and content of the survey had to be explained to each person a survey was handed to. There was an extra sheet with all information on accessing the results for the person to keep after survey completion. It was crucial for the student or staff member of GeoTenerife to stay with the person completing the survey in case of any questions. The surveys were collected after completion, numbered, and the data was compiled into an excel spreadsheet using a coding system. 

This report focuses on people’s perceptions of different volcanic Hazards and how this may differ depending on the island on which they live and their age.

Difficulties and Challenges Encountered During Project

Multiple difficulties and challenges were encountered during this project. Most of our days in Tenerife and La Palma were spent as field days. We were often working in rural locations and completing work tasks that weren’t to do with the surveys. This meant that we didn’t always bump into people and even if we did it would be on a ten-minute stop at the gas station. We also discovered quickly that the surveys can take anywhere between 10 – 20 minutes for people to complete. Due to the number of questions and length of time it takes to complete the surveys, it was often hard to find people in a suitable setting and/or environment to fill them out. This meant finding the right place and time to do the surveys was a real challenge at points. Many people were usually working too which added an extra element of difficulty. We overcame this by leaving surveys with people at specific locations and picking them up at a later date. 

One of the biggest challenges we faced was the language barrier. Most of the interns are not fluent in Spanish and this was a real difficulty when first handing out the surveys. It also made it harder to answer questions that the participant had throughout completion of the survey. We tried to overcome this challenge by getting Spanish speaking colleagues to be present whilst handing out the surveys. If there were no Spanish speaking colleagues, we had a piece of text written in Spanish that explained the principles and aims of the survey. 

Another challenge we faced was ensuring we surveyed people from a wide range of age groups and backgrounds. Many of the people we met during the day were elderly. Many of the people from the younger age categories were those that worked in the visitor centers and for INVOLCAN. This would have created a skew in the data and impacted how representative the dataset is of the population as a whole.

Conclusions

We compared how participants from Tenerife and La Palma perceived the likelihood of natural hazards and how prepared they felt to cope with these hazards. We found that in general, participants from La Palma perceived the risk of either a volcanic eruption or earthquakes affecting their community as ‘Very likely’ compared to participants in Tenerife, likely due to their recent experience with these hazards in the 2021 eruption.  Most residents in both islands perceived the risk of a volcanic eruption as either ‘Very likely’ or ‘Somewhat likely’ however, suggesting that the average resident is aware that they live in a volcanically active area that could potentially be affected by an eruption. 

Age was found to affect perception, with older and younger participants tending to perceive the risk of volcanic eruption as being lower compared to middle-aged participants. Dividing this data by island revealed clearer patterns in the data, showing that participants in La Palma generally agreed on the perception that a volcanic eruption was likely to affect their community, with age groups 45-54 and 55-64 almost unanimously agreeing with the statement a volcanic eruption was a ‘Very likely’ phenomena to affect their community. This age range may be some of the most affected by the 2021 eruption, with houses, jobs and businesses lost to the eruption. Tenerife showed a similar trend, with the same age groups showing high agreement, but with the ‘Somewhat likely’ statement. This suggests a potentially complacency when considering the risk of volcanic eruption amongst the population of Tenerife, however recent events in La Palma may have changed this.

We found that people that live on the island of La Palma felt more prepared in case of a volcanic eruption and know the potential hazards and risks these pose, probably due to their recent experience of a volcanic eruption in 2021. As the eruption caused significant damage and ruined many people’s livelihoods, many were anxious of the potential for another eruption, and felt that they would not be able to manage their emotions and feelings. Participants in Tenerife however felt more confident witnessing the event from afar and most would not have been directly impacted. However further surveys must be conducted to improve the reliability and validity of the results.

Participants feedback suggested that the survey could be more streamlined, and whilst often received well in Tenerife, in La Palma residents were more sensitive to the questions, suggesting that it may not be suited to locations that have recently been affected by a volcanic eruption.

Next Steps:

• Survey more people, from other islands, more age groups and a wider range of socio-economic backgrounds
• Analyze other data patterns and relationships – eg. Educational level and perception of risk
• Compare to data from other locations around the world

Acknowledgments

Thank you very much to all students and staff of GeoTenerife 2022 for handing out surveys. A special thanks goes to Ana Clara Pelliciari Silva, Tamsin Backhouse and Ignacio Garcia for all their invaluable help with translation.

Note/Disclaimer

This report presents a first approach to the data and it is part or a pedagogical exercise of interpretation. The conclusions presented here are tendencies observed in a first descriptive analysis and should not be considered definitive.

References

AlQahtany, A.M. and Abubakar, R. 2020. Public perception and attitudes to disaster risks in a coastal metropolis of Saudi Arabia, International Journal of Disaster Risk Reduction, 44(101422)

Anguita, F. and Hernan, F. 2000. The Canary Islands origin: a unifying model, Journal of Volcanology and Geothermal Research, 103, 1-26

Longpre, M-A. and Felpeto, A. 2021. Historical volcanism in the Canary Islands; part 1: A review of precursory and eruptive activity, eruption parameter estimates, and implications for hazard assessment, Journal of Volcanology and Geothermal Research, 419, 1-23

Martí, J., Becerril, L. and Rodríguez, A. (2022). How long-term hazard assessment may help to anticipate volcanic eruptions: The case of La Palma eruption 2021 (Canary Islands). Journal of Volcanology and Geothermal Research, p.107669. doi:10.1016/j.jvolgeores.2022.107669.

Written by Jacob Nash

Research summary

Aerial and submarine drone survey of the 2021 Tajogaite Lava flows and lava deltas to identify geomorphological, structural, and ecological locations of interest, completed between the 06/09/2022 to 09/09/2022. The 3D models produced from these surveys are available to view on our 3D Drone Models page as part of GeoTenerife’s #VolcanoStories project.

Case Study 

Tajogaite Eruption of Sep. 2021 to Dec. 2021; La Palma (Canary Islands, Spain). On the 19/09/2021 a basaltic fissure eruption began at Tajogaite Volcano located on the Cumbre Vieja Ridge, following a series of seismic swarms recorded since 2017 (Global Volcanism Program 2021b; Pankhurst et al. 2022). Lava flows travelled west up to 6.5 km to the shore and continued 1.1 km into the sea forming a lava delta (Carracedo et al. 2022). The eruption ceased on the 13/12/2021 (Global Volcanism Program 2021a; Carracedo et al. 2022)

Survey Location(s)

Lava flows and lava deltas of the 2021 Tajogaite eruption (Figure 1A). These Lavas have been identified as alkali basalts enriched in olivine, pyroxene, and amphibole (Pankhurst et al. 2022). Six zones of interest were identified for the aerial surveys: 

• Zones 1 – 2: 2021 southern and northern lava deltas (Figure 1B) – The focus of this report 
• Zone 3: Base of main eruptive cones at Tajogaite 
• Zone 4 – 6: Different heights across the lava flows between the main cones and lava deltas

Zones 1 – 2 were identified as zones of interest for the submarine drone survey.

Aims – Investigating the 2021 Lava flows and deltas for any features of interest that might affect the local population, using two techniques:

1. Aerial Surveys – Identify and monitor geomorphological, structural, and ecological changes on the 2021 lava flows, develop digital elevation models (DEM) of the 2021 lava deltas, collect data that can freely be utilised by geoscientists and to stimulate interest in Earth Science.  
2. Submarine Survey – Initial aim was to investigate the state of the submarine environment including vegetation growth, erosion and/or other noticeable geological processes present on the 2021 lava flows/delta that entered the Atlantic Ocean. However, permission was not granted by authorities to access 2021 lava flows. Aim was changed to investigation of the areas surrounding the 2021 lava flows/deltas and the 1949 lava deltas to identify and geomorphological and ecological changes.

Aerial Survey Field work – Aerial flights were performed at all six zones of interest using the DGI Maverick 2Pro Drone (Figure 2). All flights were performed by Fernando Borras Castello. The drone has a GPS receptor allowing it to place coordinates on the images it takes. The drone was flown across the landscape/landform of interest constantly taking photos of the ground below. Aerial surveys of Zones 3-6 were performed without the presence of GeoTenerife interns. Interns were present at for flights at Zones 1-2. 

Zones 1-2 – Three aerial surveys were completed:

• 07/09/2022 – Survey undertaken from Mirador Las Hoyos (28o 35’ 46’’ N 17o54’43’’W, Figure 1B & Figure 3). Four individual flights were performed with the aim to generate an entire overview of the southern 2021 lava delta, lava slopes and the 1949 lava delta that the 2021 lavas flowed onto (Figure 3). All flights were taken at a hight of 150m. Flight 1 photographed the lava slopes (Figure 1B) as such the photos were taken at 45o to the zenith. Flights 2-4 took photos at the zenith angle. 
• 08/09/2022 – Three surveys were performed. The first survey consisted of one flight from a viewpoint overlooking the southern 2021 delta at a hight of 100m. The second and third surveys were performed a top Montana la Laguna (28o37’32’’N 17o54’52’’W, Figure 3). The second survey consisted of one flight at 150m with the aim to provide an overview of the northern lava delta (Figure 1A). The third survey consisted of a pre-programmed flight at 150m imaging a hollow channel structure. 
• 09/09/2022 – Aerial surveys were taken from a boat at a distance of approx. 800-900m west from the 2021 lava flows exclusion zone (Figure 3). Two flights were undertaken photographing the underwater sections of the 2021 lava deltas. 

Submarine Survey Field Work – All submarine surveys were undertaken using the FIFISH V6 drone (known as Fifi). Denied access to the 2021 lava flow deltas meant that the submarine drone surveys explored the ecology and geomorphology of the ground beneath the boat including volcanic sand dunes. 

Data Processing – Photos taken during the aerial surveys were analysed using DCIM PIX4D. This software selects points of interest in the photos e.g., colour, shape etc, and of known coordinates (using the GPS in the drone). By identifying the same point in multiple images the software can locate the point in an XYZ coordinate system. The software identifies > 200,000 points, this is known as a dense point cloud (DPC). The DPC is then analysed to create a digital elevation model (DEM). 

Results – DPC models and DEMs of the northern and southern 2021 Lava slopes and deltas (Figure 4) and the main Tajogaite cone were developed. High definition photos of the lava flows were produced to be used in ecological surveys (Figure 5A). The submarine drone took numerous photos of the sea floor including volcanic sand dunes (Figure 5B).

Discussion: The DPC models and DEMs show clear images of the 2021 lava slopes and deltas. We can clearly identify the transitions between the lava flow, lava slopes, and deltas. Specifically, on the lava flows the models clearly illustrate the geomorphological features present including a possible collapsed lava tube on the flows that feed the northern delta (Figure 4C). Regarding ecological changes, the images taken to produce the DPCs and DEMs were taken at heights insufficient to perform detailed ecological surveys on the lava flows but can be used to locate regions of interest for ground based surveys. Submarine surveys provide a new angle on investigating geomorphology and ecological changes but require further work within the exclusion zone to provide information on the 2021 lava flows. However, the drone surveys and generated images can be utilised by geoscientists to provide a new opportunity for improved understanding of lava flows and delta structures, which can subsequently be used in hazard management and mitigation as well as post-eruption responses.

Future Work: We recommend that the majority of future work focus on the submarine drone surveys to investigate the ecological changes and geomorphological structures on the 2021 lava deltas that are submerged underwater. For future aerial surveys we recommend focused flights on individual structures within the lava flows, specifically structures that may change over short periods of time and that may impact anthropogenic structures such as the lava slopes and channels. The collapse of these structures and potential land-slide possibilities may have a direct impact on local populations and anthropogenic land-use. Areas of interest away from the lava deltas and slopes remain the vents of Tajogaite, as well as the performance of surveys at lower altitudes (<100m) to provide images of greater detail (e.g. Figure 5A) which can be utilised in ecological surveys. More detailed images alongside DPCs of the lava flows can be used to determine locations for ground based ecological/vegetation surveys.

References:

1. Carracedo, J.C., Troll, V.R., et al. 2022. The 2021 eruption of the Cumbre Vieja Volcanic Ridge on La Palma, Canary Islands. 37.
2. Global Volcanism Program. 2021a. Report on La Palma ( Spain ) — 15 December-21 December 2021. 2021–2022.
3. Global Volcanism Program. 2021b. Report on La Palma (Spain) — 15 September-21 September 2021. 2021–2023.
4. Pankhurst, M.J., Scarrow, J.H., et al. 2022. Rapid response petrology for the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands.

Written by Sofia Della Sala and Brannock Hackett

Introduction and Rationale

Lava flows are fresh rock that can be colonized by vegetation over time. Though this can be a long process, it is important to understand how various types of vegetation may colonise lava flows and over what timescales, to be able to monitor the development of vegetation on lava flows. In this study, the vegetation of lava flows was investigated for lava flows of different ages on the Canary Island of La Palma.

The amount and maturity of vegetation of lava flows from eruptions in 1677, 1949, and 1971 were noted and described to understand how vegetation differs with age of lava flows and within different locations. Multiple areas of 1 x 1 m^2 were studied on each lava flow to gain an insight into the vegetation that might be growing on the lava flows from last year, the 20th century and nearly 500 years ago.

Geologic Setting and Eruptive History

The Cumbre Vieja is an active 25-km long volcanic ridge (from 28°42’18”N, 17°50’44”W, elevation of 2058-m to 28°27’30”N, 17°50’37”W, elevation of 79-m) on the southern flank of the island La Palma in the Canary Islands. There are approximately 67,839 people who live on either side of the ridge and therefore are vulnerable to volcanic eruptions. 

Within the last 450 years there have been seven recorded volcanic eruptions on La Palma, all of which have produced both lava flows and variable volumes of tephra with eruptions in 1677 and 1949 having phreatomagmatic phases (Figure 1). Furthermore, the latest eruption in 2021 produced both effusive Hawaiian-style lavas, and more explosive, tephra-producing phases. Eruptions are more prominent on the western flank of the ridge, except the eruptions in 1646 and 1949 which occurred on the eastern flank.

Methods

Surveyable points on all four lava flows were identified. The boundaries of the lava flows were surveyed as well as five meters into the lava flows. The quadrant sections were chosen at random.

The sections of lava surveyed were chosen based on accessibility from nearby roads. Upon reaching the edges of the lava flows, the 1 x 1 m^2 quadrants were placed on the lava at random and the features of the rocks as well as the presence of any vegetation were recorded (Figure 2). This was repeated at least six times at each lava locality. The lavas surveyed included the 1677 eruption, the 1949 and the 1971 lavas.

The lavas were surveyed at low, mid and high altitudes in order to ascertain whether there were any differences in vegetation at different points along the lava flows. 

The criteria that were noted included: location, date and time, surface description, rock description and presence of vegetation (description of what vegetation, surface coverage, and direction).

Figure 2: Examples of the laying of the quadrats at various points along the lava flows and in tephra at the lava flow edges. The grids are 1m x 1m, in 50cm segments.

References

Carracedo, J.C., Troll, V.R., Day, J.M., Geiger, H., Aulinas, M., Soler, V., Deegan, F.M., Perez‐Torrado, F.J., Gisbert, G., Gazel, E. and Rodriguez‐Gonzalez, A., 2022. The 2021 eruption of the Cumbre Vieja Volcanic Ridge on La Palma, Canary Islands. Geology Today, 38(3), pp.94-107.

Written by Anabel Pozniak and Gemechu Bedassa

1. Introduction 

1.1 Aim

This report aims to assess the risk of an imminent effusive eruption in La Palma within the Cumbre Vieja Natural Park if seismic trends continue to occur in this region. An exclusion zone will be developed based on an eruption simulation if past volcanic eruption data fits with this model. The report will assess the region where the volcanic eruption could occur, by using probability data from past eruptions so future eruptions can mimic these. GIS and seismic data have been used in conjunction with statistics to assist in the assessment of volcanic eruption risk. 

1.2 Regional Setting 

The Cumbre Vieja is an active 25-km long volcanic ridge (IGN 2022) (from 28° 42’18” N, 17° 50’44” W, elevation of 2058m to 28° 27’30” N, 17° 50’37” W, elevation of 79m) on the southern flank of the island La Palma in the Canary Islands (Figure 1 and 2). There are approximately 67,839 people who live on either side of the ridge and therefore are vulnerable to volcanic eruptions.

1.3 Geological context 

The geology of La Palma comprises of two major volcanic domains. The first one is, the older volcanic series (1.7 Ma to 400 ka), which includes the Garafia volcano, the Taburiente shield volcano with Cumbre Nueva and the Bejenado edifice (Klugel et al., 2017). This volcanic domain is an enormous, truncated cone shaped relief with a semi-circular plant that currently rises to 2,426 m (Roque de los Muchachos), with a large central depression of erosive origin called the Caldera de Taburiente (Figure 3). It is mostly dominated by basaltic flows that are crossed by basic vertical-subvertical dikes. This part of the Island is, at present, totally inactive.

Now, Volcanism migrated southwards (∼0.5 Ma) to the second volcanic domain (Cumbre Nueva and Bejenado units) through the eruptive fissure of the Dorsal or Cumbre Vieja (Marrero et al., 2019). This domain is structured by an eruptive axis aligned in the north-south direction containing two known volcanic sectors; Cumbre Nueva (northern sector) and Cumbre Vieja (southern sector). In the last 500 years, the seven historical eruptions including the 2021 eruption have taken place on the Cumbre Vieja ridge. The main volcanic products resulted from the historic eruptions include basic alkaline rocks (alkaline basalts, basanites, trachyba-salts, and tephrites) and pyroclastic deposits of strombolian character.

1.3.1 Historical Eruptions 

The Canarian Archipelago have been through a total of 19 historic eruptions. Of the 19 eruptions, 8 of them (1470, 1585, 1646, 1677, 1712, 1949, 1971, and 2021) occurred on the Island of La Palma (Figure 4). This confirm us, La Palma Island is one of the highest potential risks in the volcanic archipelago of the Canaries (Fernando et al., 2021). Nearly all historic eruptions on La Palma were relatively moderate, restricted to regions in the island with limited extension and mostly last from a few days to 3 months. These historical eruptions have traditionally been considered as quite eruptions, with slight explosions (VEI 1-2). The eruptive behaviour is mostly attributed to fissure mafic eruptions, low VEI and typical Strombolian eruptive styles.

1.3.2 Seismicity 

The historic seismicity in the Island of La Palma was due mostly to volcanic activity. Most of the eruptions were preceded by seismic swarms which lasted from days to weeks and were felt by the population of the island. But, starting 1980’s, very few earthquakes with a diffuse epicentral distribution running in an east-west direction has been recorded. In the era of no measuring instrument, numerous earthquakes occurred during and after the historic volcanic eruptions in 1470, 1585, 1646, 1677, 1712, 1949 and 1971(Romero, 1991). Magmatic activity that does not result to a subsequent eruption also resulted to earthquakes (Figure 5) occurred in the years 1920, 1936 and 1939. More recently, in 2017 and 2018, anomalous seismicity with about 300 earthquakes at a depth of about 25 km and with about 1000 slightly deeper earthquakes were detected (López et al., 2018; Fernando et al., 2021).

The latest eruption (2021) in the Island of La Palma was preceded and accompanied by several phenomena, such as ground deformations and seismic activity (Luca et al., 2022). Accordingly, about 4,222 earthquakes were detected before the 2021 eruption by the Spain’s National Geographic institute in areas of the Cumbre Vieja national park, around the Teneguia volcano in the far south of the island. Eventually, more than 22,000 earthquakes were detected throughout the eruption. Such an increase in frequency, magnitude, and shallowness of the seismic activities were an indication of a pending volcanic eruption, which occurred on 19 September.

1.3.3 Future eruptions in La Palma 

After the 2021 volcanic eruption ended in December 13, the low-level seismic activity continues including no signs of tremor signals although quakes are not ruled out. The ongoing seismic activities after the latest eruption are important indicators to explain possible future volcanic activity in the Island.

2. Methodology 

2.1 Seismic data and vent location 

In this work, seismic data recorded across the last 90 days across La Palma by the Instituto Geográfico Nacional (IGN 2022), seismic data recorded before the 2021 Tajogaite eruption, and the location of historic vent and hydro magmatic eruption locations (Marrero et al, 2019) were used to predict the future eruption to occur in the southern volcanic domain of the Island. 

2.1.2 Lava flow simulation 

Potential flow of lava was modelled using the Q-LavHA plugin for QGIS and a DEM (Digital Elevation Model) from the Copernicus Land Monitoring Service EUDEM. The point of origin was predicted to occur to the north of Lavas la Malforada, the northeast limit and highest elevation of the seismic swarm. Parameters like those observed in the 2021 eruption were used to model the flow of lava, with a length of 6.2 Km and default lava coverage probabilities used. 

2.1.3 Event Tree 

Shows the statistical likelihood of volcanic hazards occurring during a volcanic eruption. Each branch of the tree leads to a more specific volcanic e.g., from a Strombolian eruption to an ash fallout. Probability estimates of the likelihood of each hazard occurring is derived using observations from past volcanic eruptions and creating an assumption that future eruptions will follow a similar trend. Seven past eruptions on the Cumbre Vieja Ridge, where a new volcanic eruption may occur, were analysed. Eruption type, hazard, and risks were grouped together for each past event. A basic probability formula was used by comparing which hazards occurred at each event to create a percentage outcome of likelihood of occurring in future eruptions. There are limitations to this method as hazards that have been calculated with low probability could still occur and are still very dangerous.

3. Results

Hazard maps and events tree suggest the eruption will be magmatic and that the lava flow will follow existing topography created in a previous eruption, creating approximately 5 lobes flowing towards the west and a spreading lobe towards the east of the Cubre Vieja ridge. These have the potential to increase risk and damage to property in the mapped exclusion zone. 

3.1 Hazard Maps 

Three Hazard maps were created. The first map (Figure 3) highlights infrastructure in the area including housing, agricultural land and communications that has the potential to be damaged during an eruption. Inside the exclusion zone, El Remo has large amounts of agricultural land whilst El Charco have more infrastructure, which are likely to be affected by the eruption.

The second map (Figure 7) displays the depth of earthquakes that have occurred on the island of La Palma between the 1st July 2022 and the 12th August 2022. Earthquakes with a depth of 12-16km are the most common within the exclusion zone, with the seismic activity forming a south-west/ north-east trending swarm.

The third hazard map (Figure 8) displays a modelled lava flow for a potential eruption. No towns are likely to be destroyed by lava flows, but agricultural land and main roads are likely to be covered.

3.2 Event Trees 

An event tree was created to show all the possible outcomes resulting from the volcanic eruption. It is likely that the eruption will be a strombolian magmatic eruption, with a 57% chance of also being Hawaiian. 

Analysing past data sets, most eruptions display more than one eruption styles, for example the La Palma 2021 eruption was both Strombolian and Hawaiian. 

If an eruption was likely to occur, it is 100% likely to have expansive lava flows, tephra/ash falls and toxic gases.

3.3 Plume model simulation 

A plume model simulation was created using PlumeRise. Figure 10 shows two models comparing a 90m (blue) wide vent and a 50m wide vent (red). Data from the 90m vent has been collected from the average vent size in La Palma, contrasted with a smaller hypothetical vent. Graph A shows how a larger 90m vent radius produces a plume with an elevation 10,000m with a downwind distance of approx. 2000m. Compared to the smaller 50m wide vent, the plume has a height of 7000m with a downwind distance of approx. 1000m. This model suggests with NE wind, the volcanic plume would closely reach the airport. 

Graph B is the calculated plume radius for the two sized vents. The 90m vent is suggested to produce a plume radius up to 10,000m in elevation and continue over the same distance as the plume produced at a smaller vent, which will rise to a lower elevation of 7000m.

4. Risk Assessment and Mitigation Strategies 

This eruption has the potential to impact the following villages: El Remo (28.5543°N, 17.8900°W) and El Charco (28.533869°N, -17.865419°W). The land surrounding El Remo is mainly banana plantations and thus a population of likely farmers. Residents in this village and the nearby village El Charco as well as residents in the northern portion of the Fuencaliente de La Palma municipality will need to be evacuated in case of a lava flow. Banana plantations in El Remo, La Zamora, and Roques las Galeras are likely to be lost and represent a hazard due to toxic fumes created when the fabric covering the banana plants burns. There will likely be an impact on infrastructure, in particular the LP-2 and the LP-210 roads, which would cause disruption to traffic travelling North to South. This eruption is unlikely to impact the airport, port, and hospital. 

4.1 Pre-eruption mitigation plan 

1. Residents in El Remo, El Charco, and northern Fuencaliente should be informed of the possibility of an eruption and loss of private land using multiple communication methods such as official letters, town meetings, and press conferences, etc. 
2. Residents in El Remo, El Charco, and northern Fuencaliente should be informed of the likely hazards, using the event tree described above, and the uncertainty surrounding prediction of volcanic hazards 
3. Residents in El Remo, El Charco, and northern Fuencaliente should have a revised evacuation plan which accounts for the potential loss of LP-2 road from a lava flow. This evacuation plan should be practiced during a drill. 
4. Implementation of gas monitoring and seismic monitoring systems around the identified eruptive zone, in order to timely change from yellow, orange, and red traffic light system. 

4.2 Mitigation strategies during the eruption 

1. Implement the evacuation plan of El Remo, El Charco, and northern Fuencaliente. 
2. If not previously changed the traffic light system should be upped to red. 
3. Establish an exclusion zone and close the Cumbre Vieja Natural Park, this will need to be monitored by rangers to prevent death. 
4. Close the airport depending on ash/plume direction.
5. All residents and tourists within 5 km radius of the lava flow are prepared for evacuation e.g, residents in Monte de Luna and Tigalate.

4.3 Limitations 

Several limitations have occurred when collating this report. It was difficult to predict where the location of the eruption might take place with very little data to support our ideas. This then impacts the decisions on the actions that need to be taken if you don not know where the eruption will occur, creating difficulty in producing a hazard and mitigation action plan. In future, more time considering the area to find a range of data such as gas emission and land deformation will help select a more likely area for a volcanic eruption. 

Furthermore, a short time span to perform hazard assessment meant that only a lava flow was considered as a hazard on the hazard maps. In future attempts, tephra/ash, pyroclastic and toxic gases will be considered. 

There were also limitations to the event tree method. Hazards were calculated from just 7 past eruptions creating an unrepresentable assessment of the likelihood, in particular hazards and risks. In future, a larger range of past eruptions will be analysed so more accurate representation can be produced. Furthermore, hazards calculated with low probability could still occur and are very dangerous, so the probabilities should not be used solely on this. 

When creating the model simulation, a range of data from different eruptions had to be used to create a simulation as similar to the predictive volcanic eruption as possible. Not all the data input was from the La Palma eruption, some was used from other Strombolian/Hawaiian eruptions. In future, a more accurate simulation could be produced if the data was all from La Palma.

Conclusions 

Our risk assessment using seismic data, lava flow simulation and event tree methods lead us to the following conclusions: 

• Based on the seismic data obtained from IGN in 2022 we predicted the eruption is most likely to occur to the NW of Lavas la Malforda (28.56157° N and -17.845230° W) on the western flank of the Cumbre Vieja ridge. 
• The hazard zontation map shows us the lava flow will follow existing topography created in a previous eruption mainly to the west of the Cumbre Vieja ridge. 
• The indicated eruption will be magmatic with both Strombolian and Hawaiian type eruption style. 
• The eruption has a potential impact to the residential buildings, agricultural lands and different infrastructures found in El Remo and El Charco areas. Therefore, residents in El Remo, El Charco and northern Fuencaliente should be informed of the possibility of an eruption and loss of private land using multiple communication methods such as official letters, town meetings and press conferences.

References 

IGN (2022). Seismicity in La Palma. URL: https://www.ign.es/web/resources/sismologia/tproximos/sismotectonica/pag_sismotectonicas/can_la_palma_en.html Accessed: 15th September 2022 

Klugel A., Galipp K., Hoernle K., Hauff F., and Groom S. (2017). Geochemical and Volcanological Evolution of La Palma, Canary Islands. Journal of Petrology:Vol. 58, No. 6, 1227–1248 

López, C., Villasante-Marcos V., Domínguez Cerdeña I., Lamolda H., Luengo-Oroz N., del Fresno C., Pereda J., Torres González P.A., García-Cañada L., González-Alonso E., Fernández-García A., Meletlidis S. and Blanco M.J. (2018). On the origin of the 2017 seismovolcanic activity in La Palma. 20th EGU General Assembly, EGU2018, Proceedings from the conference held 4-13 April, 2018 in Vienna, Austria, p.7694. 

Luca C.D., Valerio E., Giudicepietro F., Macedionio G., Casu F., and Lanari R. (2021). The September 2021 eruption at Cumbre Vieja volcano (La Palma, Canary Islands): investigation on the pre- and co-eruptive phases through DInSAR measurements and analytical modelling: EGU22-12844. 

Marrero J.M., García A, Berrocoso M., Llinares A., Losada A.R. and Ortiz R. (2019). Strategies for the development of volcanic hazard maps in monogenetic volcanic fields: the example of La Palma (Canary Islands): Journal of Applied Volcanology.8:6 

Paolo F.D., Ledo J., Ślęzak K., Dorth D.M.V., Pérez1 I.C. and Pérez N.M. (2020). La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion: Scientific Reports | (2020) 10:18181 

Romero, C. (1991). The historical volcanic manifestations of the Canary Archipelago.

Written by Ajay Wynne Jones and Kelsey Hewett

Introduction

Chemical analysis techniques are commonly used by geoscientists to determine precise compositions of bulk fractions of rock. For the Department of Geological Sciences at the University of Florida, the use of a new XRF spectrometer will introduce highly precise geochemical analyses of lava and tephra surfaces. A hand-held XRF, or X-Ray Fluorescence, is a type of analyser that focuses on a very small area of material to collect bulk and trace elements to determine the overall composition of a sample surface, in this case, volcanic rocks. 

The research conducted in La Palma is just one small piece to a bigger scientific picture related to the recycling of Earth’s crust and determining what processes are the most important for making volcanic material bioavailable. This is valuable research as the concentration and variation of chemicals within volcanic rocks may have affected the evolution of early life.

In order for this research to begin, rock samples are needed from various ages. Here in La Palma, a volcanically active island of the Canary Islands, there are distinguishable features of the landscape by the many lava flows of the Cumbre Vieja volcanic complex. The permit gathered for this project allowed 6 sample locations collected on 3 lava flows, the 2021, 1949 and 1585.

Method

The locations selected from the permit are representative of mid and low altitudes of the 2021, 1949 and 1585 lava flows. Biologic indicators, like vegetation, vary based on conditions from altitude, thus, it was essential to collect samples of lava from the same eruption from multiple areas. Samples were collected from the center of the flows and only at the surface. This was done to reduce any possible contamination from the lava flow margins. Tephra/ash samples from the 2021 eruption were collected from multiple sampling locations and collected by hand-scooping only the top surface layer. 

While out in the field, the method for collecting samples included filling out a table indicating the date of collection, lava flow age, sample name (e.g. GT-LP-21.1), sample type (rock or tephra), location using UTM, and elevation with any error if given. Sample bags had the sample name and date written on them. Pictures included a scale and a view of the sample in-situ before removal. GeoInterns wore hi-visibility vests, hard hats, gloves while using a rock hammer, eye protection and masks. The goal of each sample was to be a minimum of 1 kg and a maximum of 5 kg.

Conclusions

During sample collection we noted that the vegetation cover on all flows was sparse, however, in particular, the 2021 lava flow, had very little indication of colonization. The oldest flow we sampled, the 1585 lava flow, had some shrubbery and grasses. Also, it was noted that the sharp edges of the Aa texture in the 2021, 1949, and 1971, lava flows had not yet been weathered down. Despite historical records suggesting a similar basanitic composition for all of these flows, the textures and vesiculation showed variation between the samples, thus there is evidence suggesting that there were compositional changes within the gas fraction of the magma.

Future research for La Palma includes trying to get a permit approved for other lava flows, including the 1430 lava flow just north of the 2021 flow, the 1712 lava flow south of 1585, and the 1971 and 1677 flows at the southernmost portion of the island. It would also be helpful to include both surface and subsurface samples to get a true distinction of the original rocks for comparison between rocks that have been exposed to the atmosphere.

The sampling conducted in La Palma was a vital component of Dr. Foster’s overarching research project on Earth material recycling and how the composition of the atmosphere has changed and lifeforms have evolved over time. As soon as the samples are received in Florida, the geochemical analysis will begin and Dr. Foster will be able to seed a new proposal to have a funded research project in this area of interest.

Written by Divas Parashar

Amongst the myriad of interesting tasks that the Scicomm students were asked to undertake, one of them was to interview the local residents of El Paso and surrounding areas to understand the situation on the ground, a year after the Tajogaite eruption in September, 2021. We had already been trained well on conducting interviews in the first week of the internship by Andy Ridgway and much of the learnings did come handy during the completion of this task. Myself Divas and my co-intern Ana went onto the ground trying to identify the right people who could tell us about the present situation. The specific goals of this task were the following:

1. To understand if there still looms uncertainty and confusion today about the eruption and the reconstruction efforts on the island.
2. If the government has been able to fulfill their promises of reconstruction and rehabilitation.
3. If the local residents are happy with the work and communication by the scientists and officials.
4. What are the concerns and problems the residents are facing today due to the eruption that need to be highlighted to a wider audience?
5. How has their lives changed due to the eruption and if we could learn something from this to prepare better for future events?

Much of the information that we gathered through our ground-work would also help the makers of ‘Lava Bombs – Truths Behind the Volcanoes’ to plan the sequel better and focus on the right themes. The goal of the sequel would be to cover the situation on the island a year after the eruption and our work would lay the foundation for a good narrative. 

I and Ana went up to random houses in the locality and rang their doorbells, hoping that the residents would be willing to spare us some time and talk to us. While some residents politely refused due to lack of time or unwillingness to talk, some others were more than happy to help us find answers to our questions. We spoke to residents in El Paso and Las Llanos, two of the areas affected by the eruption, directly or indirectly. Our interviewees were from diverse background, ranging from housewives to saleswomen to business owners and this helped us get a wide range of perspectives on the issues. 

Personally, it was a humbling experience for me to be able to talk to residents and hear their stories about the eruption and everything that has happened as a result of it. They spoke to us about the problems they are facing, ranging from uncertainty and confusion regarding the reconstruction and rehabilitation efforts, the unavailability of the promised help from the local government and the slow progress in everything. We also realized that there exists a strong fear amongst the residents that the volcano might reactivate and cause more damage in the coming weeks or months. This speaks volumes about the lack of proper scientific communication by the scientists and officials. Many of their lives have changed forever after the eruption, but there exists a hope for a better future. We are glad that our interviewees opened up to us about a sensitive matter and had a conversation that isn’t always easy.

We hope that the work that we have done will help the makers of the sequel of Lava Bombs documentary to focus on the important matters and cover the themes that will bring about a positive impact, not only for the residents of La Palma but also for disaster zones across the globe. As for us, we return home with some memorable conversations and moving tales that we shall remember for a long to come. The skills that we have learnt in the past 4 weeks, not only in theory but also in practice shall go a long way in shaping our futures and the lives that we carve for ourselves and those around us.