Thursday, 25 June 2015

Day 4 - Adios Tenerife! Hola La Palma!

So today is the day! 

Myself and Hannah leave Tenerife for three weeks of work on La Isla Bonita; the beautiful island of La Palma. We met our trusty 'teacher' who will guide us for the next three weeks, at the port on Tenerife. Samara Dionis is a PhD student at InVolcan, who has her viva on the 3rd July. Fingers crossed Samara! Her second in command is Paulo Teixeira who is a member of the technical team at the Observatório Vulcanologico de Cabo Verde (OVCV) and the Instiuto Nacional de Meterológia e Geofiśica (INMG).

Leaving La Palma

La Palma is the fifth largest of the Canaries covering a total area of ~706km2 and the second tallest at 2426m asl. It is located to the northwest end of the archipelago.

The Canary Islands; La Palma top left

The island is elongate following a N-S axis and is easily separated in to two distinct units; the older Seamount Series (4 - 2.9 million years old (Myr), associated with the submarine volcanics and the Coberta Series which forms the sub-aerial part of the volcanics. Most of the island is covered by the Coberta Series and its sub-series the Taburiente Series (2 - 0.6 Myr) and the younger Cumbre Vieja volcano (0.6 - 0 Myr). The Taburiente series to the north, consists of the Taburiente stratovolcano, the Bejenado stratovolcano and the Cumbre Nueva edifice. The southern part of the island is made up of the Cumbre Vieja volcano. An elongate Hawaiian style rift volcano with in excess of 15 cones and eruption centres along its ~23km crest, with its highest point of Pico Birigoyo 1950m asl to the north.   

Aerial image of La Palme (photo credit to Sergio Socorro)

At the centre of the northern part of the island there is the Taburiente Caldera. This is not a caldera in the classic geological sense, but more a translation sense. It is a large crater that has not formed by means of collapse as a classic caldera forms, but instead has formed due to aggressive erosional processes. This erosion has exposed the submarine stratigraphy of the upper Seamount Series. Kilometres of pillow lavas line the walls of the caldera with dyes, sills and sheeted dykes cutting the pillow lavas in all directions. The intrusions are made up of peridotite, pyroxenites, anorthosite, gabbros and syeno-gabbros.

All volcanic activity on the island is currently concentrated to the south along Cumbre Vieja, the most active in the Canaries. The most recent eruption occurred to the very south part of the island from Volcan de Teneguia in 1971. Most of the eruptions have been strombolian and phreato-strombolian in style and studies of olivines from the lavas indicate interaction between recycled lithosphere, depleted mantle and mantle plume.

Geologists have shown increased interest in Cumbre Vieja in recent years, particularly since the 1949 San Juan eruption. Associated with this eruption is the development of a west facing fault system along the crest of Cumbre Vieja (northern third). The eruption was the most explosive on the Canaries during historical times and the faults are believed to be the first surface rupture along a zone of flank instability.

See Padrón et al. (2015) for details of references.

Here in the Canaries, the gases monitored closely are CO2 and Helium. The main reasons for targeting these gases is because Helium is very stable under most conditions and CO2 is chemically inert; that is, it does not react chemically.

The soil gas and temperature surveys are carried out during the summer months when the weather is better, mainly because high winds and rain (though La Palma lacks greatly in the latter!) can affect gas concentrations.

The definition of an active volcano is "a volcano that has erupted in the last 10,000 years and/or has surface emanations including fumaroles, geysers, steam jets, steaming ground, bubbling springs, surface temperature anomalies, notable gas fluctuations and inflation/deflation of the edifice and surrounding areas". Based on this the only island within the Canaries that is believed to be extinct is La Gomera.

Volcanic hazards monitoring is vital not just in the Canary islands but in many areas around the world, especially if those areas are populated in any way. Such monitoring allows for scientists of various disciplines to advise populations who live on or near to active volcanoes, of any potentially pending activity that could be hazardous to those nearby. Safety procedures are developed in accordance with the population and in extreme cases, evacuation procedures also. Though it does not apply to the Canaries, there are many populations who worship their volcano. There will be ceremonies and offerings made to appease the volcano. Many people in poorer countries rely heavily on the fertile volcanic soils to make a living and will often refuse to leave their lands and livestock behind. Safety and evacuation procedures are developed to take such aspects in to consideration. But sadly, no one can force someone to leave their home, even in such a situation as a volcanic eruption. Mount Merapi in Indonesia and the tribes people who live in its shadows are an example of this.

In the case of geothermal exploration, the same soil gas sampling methods can be used to observe CO2, Helium, Neon, Hydrogen, Nitrogen, Oxygen, Methane and Hydrogen Sulphide values depending on what is already known about the area of interest and what is needed in the area of interest. Such information is coupled with surface temperature records and efflux measurements taken in situ. This again can vary, looking at CO2, Hydrogen Sulphide, Methane, Sulphuric Acid, Helium and Hydrogen, though the last two are rarely used as they are  much more complex. In La Palma, CO2 efflux is the only one that is required.

We will be staying in the municipality of Fuencaliente and the town of Los Canarios, towards the south of the island, almost at the end of the volcano trail of Ruta de Los Volcanes (see Day 9!).
This municipality includes the youngest land of La Palma and the Canary Islands. In the last 400 years there have been 4 volcanic eruptions that have produced large lava flows that have left their mark on the landscape and extended the island seaward. The municipality is 56km2, including the coastal region of the southern tip of the island. From here to the opposite side of the municipality, Fuencaliente reaches an altitude of 1600m.

Within this small area you can move from the beautiful pine forests to desert-like terrain of the lava fields and find grape vines growing deep within a volcano to agriculturally developed lands where figs, bananas and mangoes are harvested, perched on the ends of lava tongues.

Two-thirds of the municipality is part of the Canary Islands Network of Protected Natural Spaces. Included in this are the Cumbre Vieja Nature Park, Tamanca Protected Landscape, Volcanes de Fuencaliente Natural Monument that includes the recent cones of Teneguia and San Antonio, Salinas Marinas de Fuencaliente as mentioned above, part of which has also been deemed a Special Area of Conservation within the Natura 2000 network of the European Union.
There is so much going for this municipality. It cares about its heritage, named after Fuente Santa, it has the longest coastline in La Palma and there are wine Bodegas everywhere!

Every day is an adventure!

Buenas noches de La Palma!

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