Lanzarote ranks as one of the most obviously volcanic places on the planet. The island is liberally sprinkled with craters, cones and lava fields. The dry, frost-free climate means that volcanic features weather only slowly, and vegetation has had a hard time gaining any meaningful foothold on the land.
Around 15.5 million years ago the island became the second of the Canaries to emerge (some time after neighbouring Fuerteventura, although geologically they are essentially the same structure), as a postulated result of continental drift over the Canarian hot-spot. Drift pioneer Alfred Wegener visited Lanzarote in 1912 months after he had first presented his theory of continental drift. His studies during his time on the island added weight to that theory.
The last major eruptive episode occurred between 1730 and 1736, when a fissure opened up in the west of the island to produce 24 main vents and several smaller ones that ultimately covered 23% of the island’s area with fresh lava. Three more vents briefly erupted in 1824 along the same general alignment, as part of what J.C. Carracedo et al described as a “structural rift-type zone”. The 18th century eruptions were not only devastating but also of great interest, particularly as they had been the first on the island for many millennia. They were possibly the last throes of a volcanic island-building process. But what had happened before that?
Corona volcanic group
As in many Spanish-speaking regions, the lava fields are known locally as the ‘malpaís’, literally the ‘badlands’. One of the largest areas of malpaís occupies the northeastern tip of the island, and is now designated as a ‘Monumento Natural’. The Malpaís de la Corona was produced by the Corona volcanic group, dominated by Monte Corona itself and incorporating the smaller, older volcanoes of La Quemada and Los Helechos. These two volcanoes grew out of the Miocene shield volcano of Famara, with Los Helechos dating to about 91,000 years ago.
Corona almost certainly provided the most recent eruption on the island prior to the 1730-36 and 1824 events. Until around a decade ago its eruption was thought to be as recent as 4,000 to 5,000 years old, based largely on the apparently ‘young’ condition of the lava field. Several sources, including official tourist handouts, continue to state this age.
However, and bearing in mind the prevailing lack of weathering on the island, it was more recently suspected that the eruptions had happened much longer ago. Accordingly, modern Argon (Ar39/Ar40) dating techniques were employed, from which it appears that Corona was active around 21,000 ± 6,500 years ago. This coincides neatly with the last glacial maximum between 18,000 and 21,000 years ago, when sea levels were at their lowest. The significance of this is explained later.
The Corona eruption left a large crater, standing 609 metres at its highest point, with a slight collapse on one side. As well as spilling westwards down the spectacular Famara cliffs, lava from Monte Corona fanned out over a wide arc to the east, creating an extensive lava field that reached to the sea along around 15 km of the current coastline. The flows (‘coladas’) were actually bigger at the time of their creation, as the coastline has retreated with the rise of sea level in post-glacial times.
Following on from the initial explosive and cone-building activity, three separate flows from Corona have been identified, the first and second partially overlaying the earlier flows from Volcán Los Helechos to the south, while the third – more viscous and more extensive than the previous flows – formed an a’a landscape that almost completely overlaid the lava field of Volcán La Quemada to the north.
The Corona tube
Within the Corona ‘coladas’ is one of the many natural wonders of Lanzarote: a lava tube that extends from the base of Monte Corona out to beyond the current coastline. In total the tube stretches for nearly 8 km and is the world’s 15th (some sources say 16th) longest lava tube discovered to date.
Created during the first effusive phase of the Corona eruption, the lava tube formed in a flow of fluid pahoehoe basalt that emanated from a lateral vent on the eastern side of the volcano, which also formed hornitos. The tube travelled roughly ESE toward the sea.
Lying under the Corona lava flow is a layer of lapilli from the initial explosive eruption, which itself lies above lava from Volcán Los Helechos. Examination of the tunnel walls suggests that the Corona lava stream that eventually formed the tunnel followed the course of a gully in the underlying Los Helechos lava. Successive pulses of pahoehoe lava built up the sides and eventually formed a roof, buoyed by gases from the flowing lava. Subsequent lavas buried the tunnel further.
As it nears the sea the tunnel dives over the end of the Los Helechos lava, leading to a more complex space with up to three chambers at varying depths in some sections, a result of internal collapses, false floors and re-routing of the flow. The tube ends abruptly in a large chamber that is 64 metres below current sea level.
Marking the route of the Corona tube on the surface are 21 jameos, the local name for a hole in the ground where the roof of the tunnel has collapsed. The jameos provide access to the tunnel, which is typically 20 metres wide, although up to 30 metres in some sections.
It has been postulated by Carracedo et al that the tunnel and lava flow originally ended where it met the sea. Studies of similar activity in Hawaii and elsewhere in the Canaries suggest that it is highly unlikely that the tube could have continued forming under the water, where a ‘lava delta’ without tubing is a more typical formation. There is evidence of some explosive activity at the seaward end of the tunnel, consistent with hot lava mixing with seawater.
Consequently, it can be deduced from the volcanic evidence alone that the tube formed above water, and that therefore the sea level was much lower 20,000 years ago than it is today. This is entirely consistent with the coldest phase of the most recent glacial period, when much more of the planet’s water was locked up in polar ice-caps and sea levels were up to 100 metres lower than where they are today.
In the following part the more recent history of the tunnel will be explored.
This week would have been more exciting than many, lately ( if i would have had time to research or watch cams.)
Mt. Lokon erupted again and georgiade provided a webcam. ( check the last thread)
UKViggen, the author of the post above, keeps us updated on Tolbachik which is set back to alert level orange ( from red) even though a new fissure might or might not have opened. A collection of beautiful images can be viewed on http://www.kscnet.ru/ivs/kvert/current_eng.php?name=Plosky%20Tolbachik.
Please check out this KVERT page about the current status of the volcanoes in Kamtchatka: http://www.kscnet.ru/ivs/kvert/current_eng.php
Obviously Santa Maria in Guatemala erupted. Erik Klemetti ( a real expert! ) devoted a post on it on his blog Eruptions: http://www.wired.com/wiredscience/2012/11/ash-fall-and-pyroclastic-flows-from-guatemalas-santa-maria/
As an ADMIN of this site, i want to state some clarifications because quite some emails reached me.
1. Carl is absent and we do not know where he is or what he is up to. I sure hope he is coming back soon.
2. Lucas Wilson is a regular READER and i/we published 2,5 posts by him but he is not a dragon (Editor) or has any influence on what we publish. He is still welcome to leave comments, but if the advertising other sites gets out of hand …
3. I am asking all people here to refrain from talking about Religions or something similar. This is a VolcanoCafe! The main topic is volcanoes, eruptions, earthquakes and the like. OT chat is of course allowed, but i really do not want to see talks about religion here. Let me say it like that: I believe Volcanoes create and destroy. This is fascinating. Let people believe whatever they want to and what makes them happy and does not harm other people.
If someone feels he/she still must go on, dragons… delete that!!!
And now to the normal Friday entertainment. AlanC and Suzie provided riddles. I know the answers to Suzie´s riddle but not to Alan`s.
RIDDLE – Name those Volcanoes!
The first shares its name with a US Armed Forces gold medal
The second was also a 1990s top-rated, psychological TV thriller
The third suggests a digitally challenged Black actor
The fourth claimed a European victory for Ireland in 1970
The fifth could have been, but wasn’t, named after Chekovs’ Masha
And finally, for the numerologists, the sixth can be represented as 16916042108
6 in words SIX points to be gained this time. I also received a hint but that will go in later.
Alans evil riddle!!
Dead straight, this one ‘ll stick to you!
What am I?
Where am I found?
Happy reading and hunting.
Have a nice weekend.