Fieldwork in the Atacama Desert, Chile

Sunday, 24 June 2012

Confessions of a Lithophile

So, very little interesting has happened in my life/work since my last post so I thought I would use my monthly update to comment on the perils of being a geologist in public, or more accurately why we should not be allowed around normal people and rocks at the same time.

At the end of May I went hiking in the Lake District with UEA’s Fell and Mountaineering Society. (Un)fortunately for them the areas of the Lakes we visited had such an interesting geology once a couple of people had asked a few questions, stupidly letting me know they were vaguely interested, I couldn't help myself in commenting in whatever we were walking over at the time.

Being in the central lakes we were mostly scrambling around on rocks of the Ordovician (around 450Ma) Borrowdale Volcanic Group; lavas, ignimbrites and volcano-clastic sediments. These formed at a time when subduction was closing the Iapetus Ocean and forcing continents together. This triggered massive eruptions which created a large and very active volcanic island arc as oceanic crust was forced under the ancient microcontinent of Avalonia (whose rocks underlie much of England and Wales, Snowdonia formed around the same time under similar conditions) which was then residing in the subtropical southern hemisphere. About as far removed an environment as possible to the peaceful misty mountains that now serve as our only reminders of this violent time.

On the Saturday we climbed Hellvellyn which appeared to be mostly made up of Lavas, many of which had a very nice amygdaloidal texture – where the vesicles (holes where gas bubbles solidified) have filled in which another mineral, often zeolite, to create a distinctive white spotty texture contrasting the dark lava rock. The term amygdaloidal (from the latin for almond; amygdale) actually refers to the stretched shape of the infilled vesicle, created by the stretching of the original bubble by the flowing viscous lava. I may have explained all this several times throughout the climb to anyone dumb enough to come up to me with a, “what’s this, it’s pretty” or similar...and then probably almost instantly regretting it as I went through an in depth explanation of the formation of these features.

Look, I've found a rock!
The next day was even worse, I forget the name of the mountain we went up – some well known scramble route near Scafell – but it was completely made up of a beautifully preserved ignimbrite, the lithified remains of pyroclastic flows (deadly currents of superheated gas and ash which can travel up to 450mph, here's a good compilation video of explosive eruptions with pyroclastic flows and Plinian plumes: pyroclastic flow movie) from explosive volcanic eruptions, which must have been pretty long lived and catastrophic to produced the hundreds of meters worth we scrambled through. Having seen recent (well around 200Ka as opposed to 450Ma) ignimbrite deposits in Tenerife on a field course in my Master’s year I knew what I was looking at and  I was amazed to see how all the features were still visible after all this time, and the rocks were still sharp – my hands and knees got shredded.  All the classic components were present, from erosional bases with low angle bedforms, showing discrete eruptional events had violent pyroclastic flows which ripped up previously deposited layers, to pumice layers and fine ash with accretionary lapili (concentrically ringed balls of ash formed as particles roll around in turbulent plumes in phoenix clouds above the pyroclastic flow) showing fallout from the Plinian plume. How am I not supposed to get overexcited and point things like this out to people?

Ordovician ignimbrite deposits, Lake District
Now this obviously isn't the first time this kind of thing has happened, a few weekends ago (when we had the one week of summer) I went to a beach with a friend. As the sea at Cromer (North Norfolk) didn’t look particularly inviting we just laid on the beach and ended up playing I Spy (I may have mentioned how cool I am). Surprisingly she wasn't impressed; it turns out syn-sedimentary faulting and onlap (in the Quaternary esturine and fluvial deposits exposed in the cliffs (Norfolk geology)) and even flint are not acceptable things to ‘spy’ if you’re not playing with a fellow geologist. Another time I was walking with a group of friends (again around the Norfolk coast) who couldn't understand my interest in the fact that the local council were using huge blocks of some sort of pyroxene (couldn't get close enough to check which) cumulate as coastal defences, as far as I know there are no large mafic intrusions around East Anglia so this must have been brought in from miles away. And on a night out last week myself and a fellow geologist were explaining to the barman the formation processes behind the zoned plagioclase phenocrysts (big white crystals) in the 'granite' bar top, even though it was just a stuck on laminate. Even my holiday photos are dominated by interesting rock formations.
Some nice bedded sandstones, near Macclesfield
Now what I am wondering is, is it time to get lithophilia recognised as a real, mental condition so that we can get help (I know for a fact I am not the only sufferer) or should ‘normal’ people just learn to accept us for who we are, love rocks and embrace the weirdo who thinks it’s normal to carry a hand lens around at all times?

No comments:

Post a Comment