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.
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.
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.
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!