I’ve been away in the field for the last few days, so I’ve been unable to post the update which I have been meaning to.
As I highlighted last week, El Hierro in the Canary Islands has been experiencing some significant volcanic activity. Since the magmatic movement began it has become clear that a submarine eruption is occurring offshore, at approximately 150 m water depth. There’s been some spectacular imagery and footage. The image to the right shows a RapidEye satellite image of the sediment plume within the water. This sediment is generated through shattering and fracturing of the lava as it encounters the cold seawater, forming a hyaloclastite. Perhaps even better though, is the YouTube footage of what the locals are calling the ‘Jacuzzi Spot’ – a bubbling mass of water, caused by the boiling of water as it comes in contact with fresh lava (below).
To get an idea of what is happening down there you need to imagine pillow lava formation – there’s a lot of decent footage of this occuring at other volcanoes (mostly Hawaii) available, but this one is perhaps my favourite:
One of the most incredible images I’ve seen is this one, however; as the pillow lavas form, lots of gas comes out of solution in the magma. This forms little gas bubbles (‘vesicles’) within the newly formed rock. These make it buoyant, hence small fragments which shatter from the main bodies of lava are able to float up to the surface. The image below shows some of these fragments floating, while still gently steaming away in the cold ocean water.
To put the seismic activity shown in the last update in context, magmatic tremor has been ongoing continuously. Below are three seismograms – The first from the start of the month showing ‘normal’ but elevated precursor activity (i.e., a few individual earthquakes scattered through the day, one from two days ago, showing a full days worth of magma tremor at high amplitude with a couple of significant peaks, and the last one is from this morning. As you can see, the amplitude is now somewhat reduced. This is likely due to the magma achieving a fairly steady state flow, no longer needing to fracture new pathways, and a reduced head of pressure. You can see the seismograms of the onset of this harmonic tremor activity in my original El Hierro post.
All seismic plots are courtesy of IGN.