With the recent flurry of media articles professing imminent cataclysmic events on the island of Tenerife, we decided to ask resident volcanologist Gerardo Vallelijes what his thoughts were on the situation and to get down to the scientific facts.
Below is his detailed response and we hope it settles the ongoing debate.
Tenerife Seismic Activity October 2017.
From 1st October 2017 up to midnight 31st October 2017, a total of 62 small earthquakes were recorded beneath Tenerife. That is an average of 2 a day.
No earthquakes were recorded on 2nd, 9th, 12th, 18th, 23rd, 25-27th making a total of 8 days with no recorded activity, meaning that on average 2.7 earthquakes were recorded on the other 23 days.
You should remember that Tenerife is a volcanic ocean island, and that in recorded history, several eruptions have occurred, the last one was in 1909 at El Chinyero.
Teide is classed as “Active but Dormant,” its actual last eruption was about 1200 years ago!
The historical eruptions were all relatively short lived – days, weeks etc. rather than years. Unfortunately what we don’t know, and have no way of knowing, is what precursory activity occurred before those eruptions.
Indeed the 2011 eruption off Restinga on El Hierro was the first eruption in the whole of the Canary Islands to be monitored from the onset of the seismic activity.
The fact as some “experts” claim that an eruption is “overdue” is frankly just scaremongering.
There is no statistical evidence to support that claim and indeed even worldwide very few volcanoes erupt to a “timetable.”
So briefly the statistics that are quoted state that an eruption occurs about every 100 years are very wrong. The chance they quote of eruption imply that one should have occurred in 2009, and back tracking in 1809, 1709, 1609 etc – they did not.
From 1704 when the vents above Fasnia opened on 31st December until 1909 is 205 years. In that period there were 5 eruptions, meaning an average of 41 years between each one.
If we count the “Columbus eruption at the Boca Cangrejo” in 1492, the interval is 417 years and in that period 6 eruptions occurred at an average rate of 1 every 69 years 6 months!
Again none occurred at that frequency!
In my opinion, the media are generating hysteria. The deep tremors are located in a region centred on latitude 28 degrees, 19 minutes, 2.64 seconds North; longitude 17 degrees, 43 minutes, 12.15 seconds West. They have a maximum depth of about 27 kilometres (about 16 miles for those who don’t understand metric!), which is south of Icod los Vinos! These may well indicate that magma is being emplaced under the island.
However that does not imply that an eruption is imminent, and there are valid scientific reasons for saying that:
1. Magma needs to accumulate in sufficient volume to be able to rise higher.
2. It needs to break a path upwards and that takes time, and causes the magma to stall as it now has to gain more volume. Rates of ascent are known to be as low as about 1 metre per day and for example 10 kilometres is 10000 metres meaning it needs about 10000 days to ascend.
3. Even if the magma ascends to almost surface level it does not mean an eruption will occur – it actually has to break through the surface to become an eruption. This is not to say that it would be ignored and once it starts to approach the surface a safety cordon will be put in place.
4. As the magma ascends various events can be expected – venting of steam if the magma encounters ground waters, gases such as Carbon Dioxide and Sulphur Dioxide – including the dangerous gas Hydrogen Sulphide which at low volumes stinks like rotten eggs, but at higher volumes paralysis the nerves in your nose and at very high volumes will kill almost instantaneously.
5. Assuming the magma reaches the surface we now have an eruption and lava will be erupted along with ashes and cinders. The lava will first fill any nearby hollows and then seek a path downhill along a barranco.
The shallower tremors that the media are concerned about may be related to the deeper ones nearer Icod, however there is no immediately obvious connection. What they imply is not clear but it is unlikely that magma has managed to work its way to a depth of about 6 kilometres near Vilaflor undetected.
So what do the tremors portend? Yes they may indicate that magma is rising into the islands basement. In doing so it is breaking a path upwards, hence the tremors.
They do not mean an eruption is imminent. It takes time for magma to accumulate in sufficient volume to be able to force a path up to the surface. For example it took over 13 years from the first noted earthquake on La Palma – July 1936 to the actual eruption in 1949.
Tenerife is monitored with various instruments including seismic monitoring equipment, tilt-meters, gas monitoring and other devices. No eruption is going to suddenly occur.
A future eruption will probably be located on the Santiago Ridge which runs from Pico Viejo to Santiago del Teide. It is expected to be of short duration – days or weeks and there will be plenty of warning meaning that there will be plenty of time to clear people away from the danger area.
Regarding Teide – the last eruption was about 850 AD – about 1200 years ago. There is a cooling magma reservoir at about sea level which is at the moment not doing much except drive off gases, and creating steam in the summit region. If Teide was to start showing signs of renewed activity it is likely that strong earthquakes would occur and be felt over a large area.
Remember the Tinerfeños say “Teide es dorma,” meaning “Teide sleeps!”
So will an eruption occur? Almost certainly – but NOT for some time yet! You have time to sink a few cerveza grandes, vinos, barraquitos, or whatever takes your fancy.
The journalists probably did some “earth science,” at school, but dropped it in the fourth year of secondary education and concentrated on media studies! They know more than those whose job is monitoring earthquakes and volcanoes. Strangely such people (including myself), have studied geology at a university to a very high level, carried out research and are the first to admit that “We know a lot, but we do not know everything.”
Journalists should concentrate on reporting the facts, not writing lurid stories about things they do not understand.
Volcanologically speaking the situation is GREEN – meaning no eruption is expected for the foreseeable future.
I would advise you to pay more attention to the local Spanish media, check the INVOLCAN website for updates. Only when you see the Tinerfeños rushing to the airport should you be concerned. So sit down, put your feet up, order another beer and remember “Keep Calm and Carry On!”