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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