Ol Doinyo Lengai – The Mountain of God

Picture from Wikipedia. The 1966 eruption.

Ol Doinyo Lengai in Tanzania, approximately 20miles (30km) to the south of Lake Natron, is one of the most peculiar volcanoes.

Whereas all other volcanoes eject silicate based lava at a temperature of 1000°c plus, this gorgeous monster, at 2980metres (9780ft), ejects molten natrocarbonate at around 5-600°C. and is the only known active example of the type.

Picture taken from Volcanodiscovery. Erupting hornito at night.

Natrocarbonate is a mixure of sodium and potassium carbonates along with a minor quantity of silicate minerals and this type of lava and ejecta so produced are called Carbonatites. The silicate minerals are silica-undersaturated suites, as feldspathoids and nepheline along with olivine and pyroxenes ie minerals with ultra-basic affinities.

When newly erupted, these rocks are dark grey to black in colour and quickly weather to a pale grey to white. Unlike silicate high temperature lavas that are incandescent in daylight, the relatively low carbonatite temperatures give a lava that is black, glowing dull red at night.

Ol Doinyo is one of the volcanoes along the line of the African Rift Valley system. This rift system extends from the Mozambique coast opposite Madagascar in the south, northwards through Africa into the Red Sea by the Horn of Africa and extends past Sinai into the Dead Sea area. This rift system is the present day activity associated with the contunued break-up of the Gondwanaland super-continent and continental drift.

Picture by Nasa

An excellent suite of photos of Ol Doinyo volcano and landforms are found here:

http://www.photovolcanica.com/VolcanoInfo/Oldoinyo%20Lengai/Oldoinyo%20Lengai.html

Carbonatite intrusives are widespread, but very uncommon and include dykes, sills, pipes and veins.

Photograph taken by Eurico Zimbres. Jacupiranga, Brazil intrusive carbonatite: Calcite, Magnetite and Olivine.

Although rare, the presence of free carbon (rather than carbonates) is not unusual in igneous rocks, as evidenced by Diamonds in widespread, but rare, Kimberlite pipe intrusions, graphite in doleritic intrusions – eg the intrusion in Borrowdale (English Lake District, the original graphite source for the Cumberland Pencil Co. in Keswick) and in extra-terrestrial carbonaceous chondrite meteorites.

Diamond in Blue Ground Kimberlite.

Picture taken from http://www.eoearth.org/article/Diamond

Alan C

Hamarinn Volcano – Burns Night

Image by Global Volcanism Program. Stunning view of the enormous craters of Hamarinn.

Hamarinn Volcano might hold the title as Icelands most over rated volcano. Why do I say that? Well, basically we are talking about the magic volcano that almost never have erupted. Actually, it probably never even erupted in 1910, but I will come back to that only known real eruption.

At best Hamarinn had a small eruption back in 1910, a weak VEI-2. But regarding the location it could equally well have been a Gjálp eruption, or a flanking fissure eruption of Bardarbunga, or for that matter Grimsvötn. Otherwise no real eruption since deglaciation. The location was set well after, and the opening was rather in between Lokis east Cauldron and the adjacent fissures of Grimsvötn and Bardabunga.

Technically Hamarinn is counted as a part of the Bardarbunga system. It is believed that Hamarinn is involved in the veidivötn eruptions. There is also a theory that it works as some sort of of connective reservoir between Bardarbunga and Grimsvötn. And judging from the imagery plotted by Lurking during the run up to Grimsvötn 2011 there might be a connection between Hamarinn and Grimsvötn. Actually there is more evidence of that connection than Hamarinn to Bardarbunga. Be that as it may.

Due to Hamarinn probably not having erupted since de glaciation the top over Hamarinn has probably solidified to much for any eruption being possible without something extraordinary happening. In a way it has become an inverted cryptodome, instead of being magma on the way up forming a new magma chamber, this is an encapsulated old chamber.

Through the volcano runs the most famous of Icelands volcanic fissure swarms, the Veidivötn, responsible for one of the two largest eruptions in Iceland since deglaciation.

So far so good, but why do I get annoyed with Hamarinn as a volcano, eruptions or not? Because now and then hydrothermal activity causes a Jökulhlaup associated with Hamarinn. And all of those get into the Global Volcanism Eruption list of eruptions. Sofar there are eleven eruptions listed that has never broken the ice, only caused a jökulhlaup, and rather small ones to boot. And yes… The harmonic tremor spikes during the Jökulhlaup. Well, duh, Jökulhlaup cause that all of their own. And to be honest, to give those small swings the eruption would have to be VEIminus1. 

Nowadays we read reports of Hamarinn erupting every other month. It is silly, we are talking about a volcano that has not provenly erupted since well before the last woolly mammoth died out. Thankfully the two new SIL-stations will put an end to this nonsense.

Jökulheimar and Dyngjufjöll has proved that the last tremoring was indeed Bardarbungas fissure swarms responsible for, and that it was in the northern swarm. Still we get reports blaming Hamarinn for it.

And one other thing that ticks me about Hamarinn. Loki-Fögrufjöll? Isn’t that a too pompously grandiose second name for a glorified inverted cryptodome?

Burns Night

Just taste how volcanically correct a name Robert Burns is. On demand I am shamelessly going to plug that it is Burns night tonight. You are supposed to drink copious amounts of whiskey, chop up enormous haggis’s with swords and listen to bagpipes. To me and any snake that is far better then painting myself green and drink beer on St Patricks Day. Since I like snakes, after all they save far more lives than they take due to killing rats. I am rather against St Patrick the Snakewhacker.

So for all snakes and poets out there. Sing Auld Lang Syne, drink up and listen to your neighbour strangling the pipes.

Sleep little Bob sleep, hush my dreamer…

Bob sleeping, hush my dreamer hush. And yes, the name is Bob. Both for baby and volcano.

During the last few days Bobs behaviour has changed dramatically. Now we are seeing bursts of harmonic tremoring caused mainly by gas movements from the magma chamber to the vent that is Bob.

What has happened is that the new magma influx have slowed down considerably, or shut down completely. This has been noticed with the severely weakened, or missing low signal frequency harmonics (0.3, 0.6 and 1.2Hz) that was earlier visible at the EOSO and EGOM stations. Those signals where associated by me and others on here as coming from a great depth, possibly even from the active hotspot mantleplume.

Image by IGN. The image shows two of Bobs splutters.

We now know that there was an active mantleplume due to the high readings of UrTh (Uranium/Thorium) in the pyroclasts taken from Bob.

That the tremor is coming and going is most likely due to that internal pressure building has slowed down so much that it can not any longer keap up a constant pressure. Also that the pressure episodes comes more apart and generaly are weaker, are also a sign that Bob might be falling asleep.

Please notice that Bob is in no way dead, all it takes is new magma coming up and the eruption will pick up spead again. Like we saw a couple of weeks ago when everyone had started declaring Bobs death. So I will here post what the requirements are for calling Bob. Also, Bob might do quite a few things to surprise us still. So it is still worthwile to watch her.

Final Signal

All measurable signs must return to the baseline before onset of pre-eruptive behaviour. Harmonic tremor must be back to background noise for one week. GPS readings might not fall that much, but they must be stable for a week. Earthquakes will occur, but they will be weak, and are a sign of the magma chamber settling from the previously stressed and inflated state. There might very well be bubbling and a heatspot at the site of the vent(s) of Bob for a very long time, so remember that bubbling is not a sign for Bob being awake. There must though have been no pyroclasts or steaming visible for a week. Silt might though be suspended into the water by heat convection from the vent.

If all of this is the case for one week, then we can call Bob, and say that he is in intermission. After a year we can say that the volcano is dormant. We will never be alive when Bob is truly dead.

With these words I will stop writing actively about Bob unless he does something unexpected (again). Next post about Bob will most likely (if things continue the way I believe) be on the one week intermission day.

On a personal note

I would like to thank all of the lovely people from Spain that together with the rest of us has followed Bob. I hope that all of you will stay here and wait with the rest for the next interesting eruption.

CARL

We are not alone out there!

Image from Part of Magellan FMIDR 20S003, centered near 18.5S, 6E. Microscopic insect or a volcano?

Yes you are at the correct site and no, I haven’t lost the plot – yet!

The following post is intended as a ‘mouth-waterer’ just to show the great variety of volcanism available.

Volcanism is not restricted to  the Earth, as evidenced by various probes sent to study other members of the Solar System. Obviously, there is an absence of rock samples – other than a few meteorites and collected lunar samples – and no direct on-the-ground observations, thus features and rock types have to be by analogy to terrestrial types. The planets of our System are divided into the Rocky planets – Mercury, Venus, Earth and Mars with a relatively thin or no atmosphere surrounding a dense ‘rock-ball’; the remainder classed as Gas Giants with very thick atmospheres around a proportionally small rock core (Pluto excluded as it is now classified as a ‘captured’ Kuiper Belt object). Throughout the System there is usually evidence to some extent of massive impact cratering associated with the Late Heavy Bombardment (LHB) 4.1-3.8 billion years ago. On our Moon the cratering seen dates from this event and it can be argued, that the Mare are ‘volcanic’ as massive lava floods released by impactors rupturing through the crust. The magmatic origin of these is not in doubt, as nunatak-like mountain peaks and relic ‘ghost’ crater rims protrude the surface; similarly some lava-flooded craters, eg Plato, have lava filled floors. These structures have not been dealt with below, not having true volcanic origins – ie extrusion of liquid material not being related to mantle plumes or to tectonism.

The information given herein has been gleaned from various web sites and acknowledge by posting as necessary.

Mercury

Mercury, imaged by the Messenger mission, shows a well cratered surface, dating in general from the LHB, together with evidence of massive Mare-like lava flooding. (It should be noted in passing, that throughout the Solar System large craters are overlapped – where this occurs -by progressively smaller, never vice versa.)  

The Messenger pictures below, show a series of clearly volcanic vents and an associated lava field.

Image Science/AAAS

 Cratering on and therefore after the lava field formation, indicates a very great age, probably towards the end or soon after the end of the LHB possibly around 3 billion years ago. That these features are well preserved is a function of lack of atmosphere hence weathering and no subsequent tectovolcanic activity.

 Venus

Venus, on the other hand, exhibits one of the most volcanically active surfaces in the Solar System – estimated at over 100,000 examples of all sizes, with over 1600 counted! These cover volcanic structures recognised on Earth – calderas, shields,domes and flows, together with some alien examples as the Tick above. The Tick,with a 35km ‘body’ is of unknown structure, possibly an eroded dome, with ‘legs’ the remains of dyke intrusions.

All images of Venus are from radar-scanned images, the dense sulphurous carbon dioxide atmosphere at 465deg C and 93bar pressure precluding normal photographic imagery. Imagery is mainly taken from the Magellan mission.
Venusian calderas are represented by large and small types ,of which Sacajawea is one of the largest at 100x150km (by comparison, Vatnajokull is approximately the same size) and is surrounded by ring faults and lavas.

Image part of Magellan C1 MIDR 60N319, centered at ~66N, 336E

The smaller form below, with a 35km crater, is clearly a collapse caldera with both radial and ring faults well developed seen cutting paler coloured lava flows. Terracing within the crater suggests the presence of a lava lake.

Image part of Magellan F-MIDR 05N228

Shield volcanoes, mostly associated with tectonic rifting, are well represented, with Sif Mons and Gula Mons, at 300 and 400km across respectively, but with corresponding heights of only 2 and 3km amongst the largest .

Magellan Press Release Image P-38724, JPL image MGN-7 2

The smaller Sapas Mons, with a diameter of a mere 120km, vertical image shows well developed flows which from their geometry, appear to be of a fairly fluid lava, possibly basaltic. The false colour radar image shows light colours over rough reflective surfaces, darker over smooth and indicates a change of lava type with decreasing age. The arrows locate impact craters.

Magellan Press Release Image P-38360, JPL image MGN-51

Anemone 1, 40km across, one of the small variety of shields, again shows the radar reflective blocky lavas radiating from the cone, with an extensive reflective lava field beyond, possibly a-a type basalt.

Part of Magellan F-MIDR 10S200, centered on ~9.5S, 201E

Volcanic domes each approximately 25km across, below, show the characteristic light radar reflectance of blocky material and this allied to the absence of obvious lava flows and the radially stretched surfaces to the domes suggests a very viscous magma as rhyolite building the domes from within.

Further Venus images can be found below

 http://www2.jpl.nasa.gov/magellan/images.html

http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/venus/intro.html

The Moon

Moving to the Earth – not dealt with here – and the Moon, volcanic activity, other than the Mare flood events, is not seen to any great extent on the Moon being limited to a few relatively small domes and cones. As the Moon is composed almost entirely of basaltic material, it is thought domes are the result of extrusion of viscous cool basalt lava and not rhyolite. However photographs of these features are very poor.

http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/lunar/Overview.html

Mars

Unlike the almost totally volcano covered surface of Venus, Mars has volcanism concentrated in 4 provinces together with extensive volcanic plains. One of the greatest shield volcanoes so far located in the Solar System, Olympus Mons, with a basal diameter around 600km (Iceland has a width – from Snaefellsness to Egilsstaðir – of around 500km) with a height of some 25000m is located in the Tharsis Province. The vast size has been attributed to the presence of a very long-lived mantle hotspot and a lack of plate tectonics, the latter as having prevented Hawaii reaching similar proportions. The periphery of Mons Olympus is a cliff-like edge some 8km in height the origin of this feature as yet unknown. High resolution images show fresh surfaces to flows, as recent as 20 million years has beed suggested.

Image Wikipedia, NASA/JPL. Comparative diagram to scale between Hawaii and Olympus Mons.Image Wikipedeia, NASA/JPL. Tharsis Province.

Olympus Mons off to the apparent north-west of 3 volcanoes – Arsia Mons, Pavonia Mons and (top) Ascraeus Mons. The green coloured area to the ‘north and west’ of Olympus Mons is a vast lava field from this feature.

 Alba Mons, also on Tharsis – the very large red region at the top of the diagram above,  is perhaps less obvious than Olympus Mons, having a very shallow slope around 0.5 degree and 7km high, but the volcanism covers a much greater area, with flow fields of highly fluid lava extending up to 1300km from the eruptive centres. The age of this structure has been suggested at c3.2×10^9 years.
Images for some Martian structures can be seen here:

http://www.lpi.usra.edu/publications/slidesets/mvolcan/volcanoes_index.shtml

The Gas giants

Moving to the Gas Giants, visible ‘volcanism’ is restricted to their satellites owing to their dense, thick atmospheres. In the case of Jupiter, of the 4 major satellites (Io, Europa, Callisto and Ganymede), the innermost, Io (with a diameter of  3642km) is perhaps the most active of all bodies in the Solar System, the volcanism/magma generation being a result of the massive tidal forces induced by Jupiter’s gravity field 422,000km distant. By comparison, the Earth-Moon mean distance is 384,400km.

Density measurements of Io (mean density 3.5g/cc) indicate a probable ultra-basic mantle surrounding an iron core whilst the surface is covered with volcanic silicate rock together with much sulphur derived from sulphide minerals. There is a marked absence of impact events and indicates the surface has been much reworked. Volcanoes, here called Paterae, resemble terrestrial calderas

Tvashtar Paterae showing lava extrusion

Galileo images November 1999 and February 2000 respectively.New Horizons probe animation of erupting Tvashtar.

Galileo image, the orange and red colours are derived from sulphur allotropes of the vent Pele, the dark grey from silicate eruptions from Pilan Patera.

Image by NASA.

Further out still, satellites of Saturn and Neptune may show cryo-volcanic activity, mainly evidenced by the Voyager probes. This activity seen on Triton, one of Neptune’s moons takes the form of ‘geysirs’ of nitrogen gas and dust particles.

Image by NASA/JPL.

If this post has sparked the imagination to look at the heavens and you want to purchace a telescope, do not buy a cheap one or one sold on magnification only; you will be disappointed. Look into astronomy magazines first; Meade and Celestron are excellent instruments.

Alan C

Hekla – Unusual Seismicity

Photographer: Kröyer (2009)

During the last 24 hours Hekla has been the recipient of 3 earthquakes and four microseismical events ranging from 0M to 0.7M. The depth has ranged from 7.5km to 0.7km. The fartherest earthquake was an 0.2M yesterday that was 5km due east. The trend has been from east to the center under the volcano proper. The seismics has trended from depth and upwards. Todays quake at 0.7 is on top of the uppermost of the magma chambers of Hekla.

Due to the logarithmic scale, earthquakes at 0M is not exactly zero, so they do exist, it is just that the scale gets a bit wonky in the really low end.

There has been no rise in the tremor levels and so far no reports of increases in gas emission. There has also been no rapid GPS motion during the last 2 weeks. Currently the borehole strainmeters are offline due to a server failure. Many of these specialized plots are piped through the server that hosts the older parts of the site. The problem will hopefully be fixed in the morning.

This behaviour is not what was seen during the last eruption. In 2000 the small quakes (below 0.5M) started about 2 hours before the eruption started. This is far more outspread.

My judgement is that this is a sign of a coming eruption. But what neither I, nor anyone else can say, is when that will happen. It is though most likely not far around the bend due to Hekla being judged to be close, since quite some time, by the IMO.

Currently we have twice the uplift and magma influx compared to 2000, we have had borehole transients, and odd seismic activity. So, the signs do really lean towards an eruption being close. Problem is just that we as always are talking about anything from in 2 hours, to somewhere in the next decade or so.

So in the end we can just sum it up as Hekla being her usual and mysterious self.

For the press

What is stated above about Hekla being close to an eruption should be understod as that she is always close to an eruption. That is her nature. Hekla currently does not warrant more than a short notice at most. And please dear lord, do not write any doom and gloom story about the end of the world. At most it will be a nuisance. Same goes for Katla.