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Scientific paper reveals massive historic Tenerife volcano flank collapse
Last update: November 7, 2011 at 4:36 pm by By
Armand Vervaeck
Written by
Dave Petley
Dave Petley is the Wilson Professor of Hazard and Risk in the
Department of Geography at Durham University in the United Kingdom. His
blog provides a commentary on landslide events occurring worldwide,
including the landslides themselves, latest research, and conferences
and meetings.
Latest news of the El Hierro volcano eruption :
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This post provides a brief review of a new paper that describes a
newly
discovered catastrophic landslide deposit in Tenerife.
One of the most intriguing but poorly understood landslide types is that of the
volcanic flank collapse.
In a volcanic flank
collapse, the side of a volcano fails, usually catastrophically, generating a
landslide.
These slides can be really big –
tens or even hundreds of cubic kilometers – and they can travel huge distances
along the sea floor. Such failures grabbed attention a few years ago due
to the potential (overstated, in my opinion) for generating a catastrophic
tsunami.
However, we understand such phenomena really poorly. There are a
number of reasons for this, principally that:
a.
They occur rarely (globally about one in every 25 years on
average), so actually recording one is a challenge
b.
the remains tend to lie in a very dispersed state on the floor of
the deep ocean. Fieldwork at 4 km water depth remains difficult,
even if you are really good at holding your breath.
However, it is one particular aspect of these landslides that remains
elusive, but is crucially important. This is the trigger of the collapse
event (i.e. of the landslide itself). Numerous mechanisms have been
proposed, including sea level change, climate change, hydrothermal pressure,
intrusion of volcanic material, and various others. It has proven very
difficult to ascertain the importance of each of these. This is an
important question if we are to reliably estimate the hazard associated with
future potential collapses.
In a
paper published in Geology this month,
Harris
et al. 2011 report a very interesting find on the island of Tenerife,
one of the Canary Islands. This is
the remains of an ancient collapse
event on the south-eastern part of Cañadas volcano.
The
landslide deposit, which is up to 50 metres thick, has been mapped across a
large area – 90 square kilometres – and this is just the onshore
component of the mass, which may extend another 50 km offshore. The
deposit consists of a classic debris avalanche material, with large (typically
up to 12 m long axis), shattered blocks in a highly disrupted, unsorted
matrix. This is typical of a highly energetic, very large collapse event.
Intriguingly, in the upper part of the deposit some fluviolacustrine
(water/lake) sediments are found in the remains of hollows, indicating that in
the aftermath of the landslide shallow lakes formed on the surface, presumably
as a result of blockages created by the landslide. Associated with the
landslide deposit are the remains of pyroclastic flows.
This is really interesting in itself, but the very well-preserved deposit
allows both highly precise dating and a reconstruction of the events that
occurred.
The dating yields a date of about 733,000 years ago,
with an error of just 3,000 years. So, the sequence of events is
interpreted as being:
- An
eruption event, termed the Helecho eruption started in
the form of an explosive event that showered ash and then pyroclastic material
across the local area;
- A
dome grew on the volcano;
- This
dome collapsed catastrophically, generating a landslide
that travelled 17 km to the shoreline, and then probably much further in the
ocean;
- Subsequent eruptions draped further pyroclastic, and then pumice, deposits on
the surface of the landslide, and rainwater collected in hummocks to form small
lakes;
So,
in this case the volcanic flank collapse was triggered by a
large, explosive volcanic eruption. Interestingly, the authors
note that
the landslide collapse left a gap in the rim of the caldera which
subsequently channeled pyroclastic deposits to the south-east.
Of course
this paper does not solve the question of what triggers
volcanic flank collapses, but it is an important data point that
validates one of the most likely mechanisms. It also provides a great
opportunity to study these landslides in detail, which should give us a much
greater insight into the dynamics of these immense mass movements.
Reference
Harris, P.D, Branney, M.J., & Storey, M. (2011). Large
eruption-triggered ocean-island landslide at Tenerife: Onshore record and
long-term effects on hazardous pyroclastic dispersal Geology, 39 (10), 951-954
: 10.1130/G31994.1
We encourage our readers to read regularly Dave Petley’s “The Landslide Blog“, probably the best in the world!
And now for my readers, erm reader...
There are rumours of wars and catastrophes worldwide. This is
a paper about Volcanic flank collapse, this may, I say again may, in the future
lead to mega tsunamis on the Western coasts of Europe and Africa, and Larger
waves striking the east coast of the Americas. We need to be aware of the
possibilities of what may come, but I hasten to add, we should not stay up at
night worrying. For one the amount of caffeine in the system could set airport
sniffer dogs howling.
I will in later posts draw together some of the possibilities
that may strike us. Carrington 2, Bolts from the blue (asteroids), Super
volcanoes, Gamma Ray Bursts and of course The promised “Three days of darkness”
Fire from heaven, Global Govs etc. I’m
just getting started.
