Chain of Dead Poets!

Amsterdam Island with visible craters.

The Amsterdam St Paul hotspot is one of the weaker hotspots around. It has created the St Paul and Amsterdam Islands, the now active Boomerang Seamount (last known eruption 1995), and an elongated chain of seamounts called the Chain of Dead Poets. These are remnants of the eruptive wake of the Amsterdam St Paul hotspot as the plates move on over it. The hotspot has had 2 episodes of increased activity after it became active. The first period lasted from 10 million years ago to six million years ago. The second period started 3 million years ago and lasts up until today. Amsterdam, St Paul and the Boomerang Seamount have all been produced during this second period of activity.

The hotspot is associated with the South East Indian Ridge and its rift system, and the chains volcanoes show evidence of changing in its chemical composition as the hotspot moved into the SEIR.

Amsterdam Island

The Island is the northernmost of the Antarctic sub-aerial volcanoes. It has had two eruptive centers down the line. Both with visible craters, the younger of the craters are far more visible on the image. Both of the craters are from periods of heightened activity, but later volcanism on the Island has primarily been of the flanking fissure type. Even though no eruption has been witnessed lava samples taken from the flanks of the younger crater shows that the volcano has indeed erupted during the last 100 years.

St Paul Island

The channel into St Paul natural harbour. One should keep slightly to the portside of the centerline of the channel when sailing in. The starboard side is much more shallow. By keeping slightly to portside of the middle you can get a 3 meter deep sailing ship into the natural harbour, well inside of it depth is not a problem, and you are quite safe regardless of weather. Stay away from the mammals on the beach, they are big and mean and are in no way to be compared to people in bikinis.

The island had a large eruption a few years before 1780 in which the predominant caldera formed. Even though the caldera is small for being a caldera it was probably formed by a Krakatoa style eruption starting with a for the volcanic system unusually large eruption with a subsequent magma chamber roof failure that let the ocean water down into the chamber. The ensuing steam explosion gutted the chamber.  In 1780 the vestigial remnants of the caldera wall facing the ocean crumbled and the ocean has during the following years carved out a fairly broad, but shallow canal that is open for smaller sailing ships due to its limited depth of around 3 to 5 meters.

Map of St Paul Island from Wikipedia. Note that the island is very small. The actual caldera is only slightly larger than 1 km across.

The Island is together with Isle du Kerguelen the best harbor in the southern ocean, and many trans-globe sailors make a port of call for repairs, or just general relaxation and landfall.

Boomerang Seamount

Not much is known about Boomerang that lies 18 kilometers north of Amsterdam Island. It rises 1 100 meters above the sea floor, but is still 650 meters below the ocean surface. During an expedition in 1996 they dredged up a lava sample and tested its Uranium/Thorium content. It showed that the lava had been erupted only 5 months prior to the visit.

The Seamount has a 2km caldera showing that the volcano has had at least one substantial eruption and probably have been a bit closer to the surface before.

CARL

The Icelandic Hotspot Hypervolcano™ – Why old traps won’t erupt again

Photograph by Jeff Shea. A range of north Greenland shield volcanoes eroded by glacier ice so that they more remind of a range of strato-volcanoes.

Earlier today commenter Lucas Wilson asked me about volcanism in Greenland. So, I thought I should write a short piece on what once used to drive the volcanism there.

But let us start with what we today call the Icelandic hotspot. In here we have a tendency to talk about large volcanoes now and then, and sometimes about what is called “super volcanoes” in the media. But, the fact is that Iceland is both the largest volcanic structure on the planet, and also by far the oldest active one.

Let us start with largest. Iceland stands for between one third and half of all the magma on the planet during the last 250 million years. The rate of lava produced is fairly prodigious. Also, few know how long this has been going on. The answer is that it all started far before Iceland was born. Time for a history lesson.

Iceland was born as the Icelandic Hotspot moved close to the Mid Atlantic Rift; Iceland was born from the mid parts to the west and the east. This is as a function of the hotspot giving extra magma to the normal volcanism of the MAR, and thusly building the volcanic edifice known as Iceland as the MAR rifts apart.

Photograph by Ansgar Walk. Trap formation eroded by Glaciers, Ice age glaciation, and coastal erotion. Baffin Island.

Okay, now to the age thing. The Icelandic Hotspot is one of the really few surface expressions on the planet that is stationary. I know, the hotspot per see is not visible, but its effects are. So, as the continents and plates have fun surfing around bumping in to each other they slide over the poor hotspot.

A few tens of millions of years ago it was a part of the North American plate that slid over the Hotspot, and as that broke apart magma pushed through and created Greenland. As the now archipelago of Greenland slid away it lost its capacity to have eruptions pretty permanently.

Before that it was Newfoundland that popped up as it slid over the hotspot. And before that we had the same hotspot creating the largest Large Igneous Province on the planet, the North Arctic Igneous Province (NAIP). Before that Labrador and Baffin Island slid over the NAIP, and that put us at about 95 million years ago. And 130 million years ago it created the Alpha Ridge. Any  super volcano will have an inferiority complex to that eruption.

Before that and even further down in time it was known as the Siberian Traps, the largest on land eruption. And now we are back 250 million years in time. Before that things get a bit harder to track.

Photograph by Jxandreani, wikimedia commons. This is a part of the Putorana-Norilsk Deposit.

Here comes an interesting thing. What is today known as the Icelandic Hotspot has been conveying about the same amount of magma since the Siberian Traps. Give or take the eruptive rate has constantly been around 0,5 to 1,5 cubic kilometer per year since day one. And as we all know the average erupted material is only 1 in 20 of the magma that comes up. The rest stays as intrusions or inside magma chambers. So, on an average year the Icelandic Hotspot will loft up 20 cubic kilometers of material.

Now some of you will say something like “Hey dude, it never erupted continuously, so it can not be the same. And dude, the Siberian Traps erupted more material than Iceland”.

The reason for it not having erupted constantly is that it need either pressure enough to crack a continental plate, or the magma had to wait for a spot that was weakened that it could crack. The Siberian Trap was a momentous episode, but the largest separate eruption was “only” 3000 cubic kilometers of lava erupted (Norilsk Deposit). In the end the Siberian Traps is only standing for a slight elevation in erupted material even though a lot of magma had accumulated under the Eurasian plate before onset of eruption. Average erupted material during the Siberian Traps was only twice what Iceland is popping out on average.

The Siberian traps carved by a river into a kilometer high cliff.

We should also remember that eruptions happen in cycles. The Norilsk Deposit is probably a hundred million year event, or in other word, it would take on average 100 000 000 years in between every eruption of that size. It is estimated that it took about a hundred years to erupt that amount. So, on average 30 cubic kilometers per eruption year and that is not a nice thing to be around, but far from what it takes to produce a mass extinction.

We know that there are about 2 to 4 eruptions on the scale of above 10 cubic kilometers in Iceland today per every thousand years. They tend to happen on a 270 year cycle. We also know that every few thousand years we get them in the 30 to 50 cubic kilometers. Most likely those come in about 1000 year cycles, but in various places over Iceland, and on average over time.

About once every 10 000 years we get one upwards to a 100 cubic kilometers. I do not know of any eruption in Iceland significantly larger than that, and would be surprised if anyone finding one. The reason of course is that the MAR creates a fairly open passageway for the magma. Norilsk was happening due to the dense rock of the Eurasian plate storing up magma under it until it cracked, so the necessary magmatic pressure can most likely not build like that in Iceland.

So, now we know that old huge volcanoes cannot erupt again due to the magma-hose being disconnected as the plates slide away from the “gas-station”, and we also know how persistant the hotspot is.

Super volcanoes, well all is relative…

Bonus Riddle from Alan

Many of you might have missed that we tend to have volcanic and geologic riddles every friday in here. Lately we did not have that due to El Hierro taking center stage. But we do know that there are many that love them, so here is bonus riddle. Remember, it should end up in something rocky.

Huh! Last week, I went into a nice bakers – they only had this rock-cake!

CARL

Sheepy Dalek – Name that Lava VIII

Lava of the Week!

Last week got a bit confused due to the mix-up of the two pictures. This time I have made triple sure that the picture shows the same as the answer.

The Score is:
3 Diana Barnes
2 Talla
2 Ursula
2 Doug Merson
2 Hattie
1 Schteve
1 Jim
1 Luisport
1 Heather B
1 Birgit
1 Jamie
1 Henrilerevenant
1 UKViggen

This week’s competition

I will award one point for the correct name of the volcanic system, one for the volcano, one point for the eruptive vent, and the final point for the lavas (minimum two correct lava types).

This week I want the name of the volcanic field, the volcanic formation on the picture, and of course the lava. So 3 points to go for.

Call for post-texts

I am soon going to become pretty occupied since I will be preparing to move, and also with work. So, if you have a good idea for a blog post, please do not be shy. Who know, you might become the next Alan.

CARL

The Kerguelen Hypervolcano™

Below the Clouds Stair-case by Swedish architects at Stockholm-based TAF Architect Office.

OK, so what in Gódabunga’s name do Swedish stairs and volcanoes have in common! Apart from the fact they can do you a real mischief if you fall down, a staircase in Swedish is trappa and this gives the name to the extensive flood basalt flows of the Traps volcanic provinces from the stair-like appearance of the flows!

Deccan Traps from: www.volcano.oregonstate.edu/vwdocs/volc_images/europe_west_asia/india/deccan.html

Kerguelen

A little known, but very extensive trap province exists in the southern Indian Ocean, some 4000km west of Australia and 1500km north of Antarctica – the Kerguelen Plateau that has developed over the Kerguelen mantle plume.

The Kerguelen Plateau – the second largest submarine plateau -  lies at approximately 1-2000 metres depth, in an abyssal depth of 3-4000 metres, and has three small island groups, Kerguelen, Heard Island and Mcdonald Island as surface expressions. The plateau extends north-westwards for c2200km covering an area of about 2.2m sq km.

Geologically, the plateau has had a colourful history, being classed as a ‘micro-continent’, it is a remnant of the break-up of the Gondwanaland super-continent and is located over the Kerguelen hot-spot. Deep water geological information is from the JOIDES ODP (ocean drilling programme) and seismic interpretation of oil prospecting data; the plateau is shown to be constructed on a general base of Cretaceous terrestrial and/or shallow water sediments – including coal horizons for at about 40m years. Volcanism began during the middle/late Cretaceous (c120m years ago) with emplacement of trachytes and basalts and continued on a large scale into the Miocene/Oligocene and continues up to the present on Mcdonald Island. Recovered ODP samples of felsic and metamorphic rock indicate the possible presence of a crystalline basement at least in part below the Cretaceous deposits. The total volume of the Kerguelen volcanic province is estimated to be in the order of 25million cu km giving an average of 0.2cu km/year. Submergence of the whole plateau was around 20m years ago.

The references below are superb!

http://www.ga.gov.au/energy/province-sedimentary-basin-geology/petroleum/offshore-southern-australia/kerguelen-plateau.html

http://petrology.oxfordjournals.org/content/43/7/1121.full.pdf

Kerguelen plateau, from Wikipedia: Kerguelen plateau topography.

The island groups involved here, are the tiny yellow dots near the north-west end on the elongate NW-SE pale blue area, Antarctica is the orange-red area at the bottom.

Kerguelen Island is the largest of the island groups surfacing above the Kerguelen Plateau; administered under the French Southern and Antarctic Terretories; covers an area of about 3400sq km and rises to 1850m at Mt Ross, the youngest volcanic expression of Plio/Pleistocene lavas – brown on the map below.

Simplified geological map of the Kerguelen Islands from Wikipedia.

The majority of the island is composed of flood basalts, in grey above, along with minor amounts of trachyte, pinkish, and the plutonic complexes (buff-grey) of Foch -north centre – and Rallier du Baty – sw bottom and the small Mt Crozier intrusion – northern of the two eastern promontories. Volcanism, related to the Kerguelen hotspot, began c40m years ago and continued until about 100,000 BP.

Heard & McDonald Islands

Heard Island and the stratovolcano Big Ben
(photo by A. J. Graff, Australian Antarctic Division)

The Heard and McDonald Islands (colloquially the HIMI) are administered by Australia and as such are home to Australia’s only active volcanoes.

Heard Island, apart from having the highest point on Australian territory at 2745m on Big Ben (9006 ft), has two main volcanoes in Big Ben, in part a 5-6km diameter, glacier covered caldera and the smaller Mt Dixon, plus small scoria cones. Big Ben, approximately 18km in diameter, is mainly of basalt/trachytic composition.

Heard Island shows 3 distinct stages of development, the oldest being the deposition of Miocene limestones 40-50my ago being found over much of the Kerguelen Plateau. These carbonates were followed around 9my ago, by 300-350m of volcaniclastic sediments and pillow lavas of the Drygalski Formation. A period of peneplanation of the Drygalski deposits preceeded the present volcanism, starting about 1my ago.

Satellite image from July 2000, showing an active two kilometre long (and 50-90 metre wide) lava flow trending south-west from the summit of Big Ben.
Photo: Thermal Alert Team, University of Hawai'i

The McDonald Island group lies about 27 miles west of Heard Island and is home to the second of Australia’s most recently active volcanoes and the whole total about 1sq mile in area, rising to 212m at Maxwell Hill. McDonald Island burst into action in 1992 after a 75,000year sleep and has been sporadically active since in late 1995-early1996, 2000-2001 and lastly in 2005 from Samarang Hill. The effect these eruptions had on the island was to almost double the size and increase the height by about100m!

The island is composed mainly of interbedded ,viscous phonolitic tuffs and lavas; phonolite being named after the resounding ‘ring’ when struck, is tough, pale coloured with a high felsic content of predominant feldspathoids over feldspar and is characteristic where a mantle plume is overlain by a thick continental crust.

2004 satellite image of McDonald Island showing island's extent in 1980 (striped).

ALAN C

Mount Erebus, Ross Island and the Age of Exploration

 

Satellite image: NASA/JPL. Released under US Gov Common

I have always had a love of the beauty of the Antarctic. When I discovered that a cousin of my grandfather had joined Shackleton’s Trans-Antarctic expeditionof 1914 to 1917 as the official photographer, this love morphed into an enduring interest in the early explorations of the Antarctic and then increased to developing an interest in volcanoes due to the descriptions I read of Mount Erebus erupting.

Mount Erebus is classified as a polygenetic stratovolcano. The bottom half of the volcano is a shield and the top half is a stratocone.  It is is currently the most active volcano in Antarctica and is the current eruptive zone of the Erebus hotspot.  Inside the crater is a persisting lava lake and shows up well in the NASA satellite image above.

Mount Erebus overlooks the McMurdo research station on Ross Island and is the largest of three major volcanoes on the island. We see above in the Nasa picture the lava lake which has been monitored since 1972, this activity has been continuous since then with many minor explosions and occasional larger strombolian explosions that throw up lava bombs to the rim of the crater. Although this activity has been noted since 1972 it is more than likely that it has occurred for most of the volcanoes recent history, because the volcano was active when discovered in 1841 and also when other later explorations took place.

The summit of Mount Erebus rises to 3,794 metres of 12,447 feet. Quite a height when you consider this volcano rises from sea level.

Ross Island

Map showing the four volcanos of Ross Island.

Mount Erubus is situated on Ross Island which was formed by four volcanoes  in the Ross Sea, only one of which Erebus is still active today. Because the ice sheet is so thick and persistent it appears as if it is part of Antarctica.

It was discovered in 1841 by Sir James Clark Ross who perhaps not realising it was an island did not name it after himself, the naming of the island in honour of him came many years later by the polar explorer Robert Falcon Scott. Ross did however name the two largest volcanoes on the Island after the names of his two expedition ship, the Erebus and Terror.

Ross Island was the base for many of the early expeditions to Antarctica. It was very suitable as a base for explorations as it is the southernmost island reachable by sea.  Scott and Shackleton both built huts on the island as bases for their polar expeditions. These are still standing and are now preserved as historical sites.

Today Ross Island is home to New Zealands Scott Base and also the largest Antarctic settlement, the U.S. Antarctic Program’s McMurdo Station.

Erebus and the Age of Exploration

Erebus was first discovered by James Clark Ross and named after his ship. Here is an interesting description of the awe it inspired in these early explorers.

Robert McCormick, the surgeon, described the discovery as “a stupendous volcanic mountain in a high state of activity“. Dr. Hooker ran to grab his notebook and quickly wrote down his reaction: “All the coast one mass of dazzling beautiful peaks of snow which, when the sun approached the horizon, reflected the most brilliant tints of golden yellow and scarlet; and then to see the dark cloud of smoke, tinged with flame, rising from the volcano in a perfectly unbroken column, one side jet-black, the other giving back the colors of the sun….This was a sight so surpassing everything that can be imagined…that it really caused a feeling of awe to steal over us at the consideration of our own comparative insignificance and helplessness, and at the same time, an indescribable feeling of the greatness of the Creator in the works of His hand“. The peak was 12,400 feet above sea level and was belching flame and smoke. Ross named it Mount Erebus and the smaller extinct volcano to the east, Mount Terror.

Members of Shackleton’s later Trans-Antarctic expedition also reported of the feelings caused by the beauty and grandeur of the volcano.

By that time the returning sun was touching with gold the peaks of the Western Mountains and throwing into bold relief the massive form of Erebus. The volcano was emitting a great deal of smoke, and the glow of its internal fires showed occasionally against the smoke-clouds above the crater. Stevens, Spencer-Smith, and Cope went to Cape Royds on the 20th, and were still there when the sun made its first appearance over Erebus on the 26th. Preceding days had been cloudy, and the sun, although above the horizon, had not been visible.

“The morning broke clear and fine,” wrote Mackintosh. “Over Erebus the sun’s rays peeped through the massed cumulus and produced the most gorgeous cloud effects. The light made us all blink and at the same time caused the greatest exuberance of spirits. We felt like men released from prison. I stood outside the hut and looked at the truly wonderful scenery all round. The West Mountains were superb in their wild grandeur. The whole outline of peaks, some eighty or ninety distant, showed up, stencilled in delicate contrast to the sky-line. The immense ice-slopes shone white as alabaster against dark shadows. The sky to the west over the mountains was clear, except for low-lying banks at the foot of the slopes round about Mount Discovery. To the south hard streaks of stratus lay heaped up to 30 degrees above the horizon. . . . Then Erebus commenced to emit volumes of smoke, which rose hundreds of feet and trailed away in a north-westerly direction. The southern slopes of Erebus were enveloped in a mass of cloud.”

NEWBY

Travelling note

Hello everybody, I am out on atravelling fot, and had suspected a bit of problem with finding internet and so on. I thought I had placed the postings on auto-pilot. But apparantly I am a full blown codiot. So I will be putting them in manually now that I have internet access again.

I have seen so many old Soviet factories during the last couple of days, that you would never believe it. I will make a special Panzer edition of the Sheepy Dalek with pictures of the tank-factory I visited. Anybody who wishes to buy a Soviet T72?

I am sorry for the low post-rate during the last few days, but with all of the wonderfull commentors in here I know there was no shortage of infomation.

CARL