On a nice sunny weekend in England (which doesn't happen a lot!) its always good to get out and about and living so close to the Lake District is always a bonus! There was also an added treat at the top, for the geeky volcanologist in me, where we stumbled across a large amount of obvious volcanic deposits! Now this isn't my particular area of expertise and the deposits were very weathered and quite old, but they looked like a volcanic tuff/pyroclastics with some large clasts (large rocks essentially) entrained inside the ashy deposit. The picture to the right shows one of these clasts very clearly.
The Lake District is geologically very old and these deposits are no different having formed around 470 million years ago in fact, something I found out after bumping into a handy information spot by an excellent pub at the bottom.
A view of one of the many outcrops.
Delving a bit further in to the root cause of these eruptions, it was mostly likely related to volcanism with the closing of the Iapetus ocean, which involved the eventual collision of England and Wales with the Scotland we see today. There are other volcanological spots in the Lake District and the UK and not all of these are as old as the Langdale formations, with the majority of them in stunning locations, especially some which are located in Scotland (Isle of Skye/Mull but to name a few!) and of course not forgetting the lovely Lake District itself. Alfred Wainwright, the man who will never be forgotten for his indispensible guide books and love of the Lakes, stated that one of his favourite spots was the volcanic area of Haystacks and as a result had his ashes scattered near the summit on Innominate tarn.
If you would like to find the Langdale deposits for yourselves, the deposits are most obvious near Harrison Stickle and Pavey Ark (in the Langdale Pikes area) in grid location NY275075 using an OS map (I hope i remembered my map reading skills) and are part of the Borrowdale Volcanics.
The question of whether there was active volcanism on Mercury has been disputed for decades, with scientists failing to produce working hypotheses for volcanism. The reason for this scepticism is that there were assumed to be a lack of volatiles beneath the surface of Mercury. Volatiles (such as CO, CO2, H2O, SO2, H2S) are needed for an eruption to become explosive, if these volatiles are allowed to exsolve from magma (via reduced pressure as magma rises) and are present in sufficient quantities, gas bubbles of volatiles can nucleate and the process of fragmentation can occur, which will give rise to explosive eruptions. Mercury has a low atmospheric pressure - close to 0 and at lower atmospheric pressures fewer volatiles are needed to create explosive eruptions. However it is not as simple as this, with some volatiles deemed as more 'important and efficient' when considering eruption processes. For example CO2 is less efficient as it tends to exsolve at greater depths, whilst H20 is the most efficient. For a number of reasons it is unlikely that H20 is present within the interior of Mercury. Any Mercurian eruptions are therefore likely to be smaller in size (Hawaiian, Strombolian, Vulcanian) or limited to effusive (non-explosive) eruptions. There are several theories as to which volatiles are present within the Mercurian inter
With the recent flybys of the MESSENGER probe interesting aspects of the surface have been definitively identified as volcanic in origin. Images of Mercury have shown evidence of a variety of volcanic features. Within the Caloris basin, wide and relatively flat shield volcanoes (comparable to the ones seen on the Moon) have been discussed by Kerber et al. (2009) with evidence of pyroclastic deposits surrounding one of these shield volcanoes. These formations provide more than just evidence of volcanism on Mercury but also that volatiles are (were) in existence within the interior. The pyroclastic deposits are hypothesised to have been formed by the equivalent of a Hawaiian lava fountain eruption. The shield volcanoes were formed by effusive volcanism in the form of lava flows. There is also further evidence of volcanism from satellite imagery in several of the Mercurian plains. Pit craters have been identified due to their steeper walls than the ones formed by impact craters. This provides some evidence of magma chambers, it is surmised that these features formed in a similar manner to caldera collapse on Earth.
Mercury orbits the sun at an average of ~58 million km and has a radius of ~2400 km.
With the entry into orbit of MESSENGER the volcanic history of Mercury will start to unravel! Still to look forward to over the next couple of weeks in my brief planetary volcanism discussions - Venus, Mars, Io and a discussion of cryo-volcanism!
Journal articles read in relation to this topic and which may be of interest:
Kerber et al. (2009). Explosive volcanic eruptions on Mercury: Eruption conditions, magma volatile content, and implications for interior volatile abundances. Earth and Planetary Science Letters 285, pp. 263–271
Head et al. (2009). Volcanism on Mercury: Evidence from the first MESSENGER flyby for extrusive and explosive activity and the volcanic origin of plains. Earth and Planetary Science Letters 285, pp. 227–242
Gillis-Davis et al. (2009). Pit-floor craters on Mercury: Evidence of near-surface igneous activity. Earth and Planetary Science Letters 285, pp. 243–250
In other volcano news, Etna is continuing its activity, with strombolian/hawaiian activity occurring over the past few days. Ruapehu (New Zealand) sustains its signs of unrest with increased CO2 degassing and maintained high crater lake temperatures.
Its taken me a while to get up and running but will now hopefully start to post more regularly.