Any Lakeland geology buffs out there?


Forum » General Forums » General discussion

By Lancashire Lad on 28/10/16 at 2:48pm

I have a couple of books on Lake District geology, but have not yet found anything that gives a clue as to what these round protrusions might be.

Odd protrusions on rocks beside Corridor Route.
Odd protrusions on rocks beside Corridor Route.

They are to be found on quite a few of the boulders and rocky outcrops when approaching Scafell Pike by the corridor route.

Size-wise, I'd say that in general they vary between 6 -12mm.

They are definitely not just stuck to the rocks, but are embedded in them. - It looks like the rocks in question have eroded/weathered away, leaving these protrusions, which presumably, must be of some harder material, behind.

I don't think, (given the volcanic nature of rocks in the area), they would be fossils of some sort. But perhaps more likely, they are a result of some process that went on during the volcanic activity.

If anyone has the answer, I'd be much obliged for any replies.

Regards, Mike.


By beth on 29/10/16 at 10:56am

I'd say "conglomerate" to sound like I knew what I was talking about. Although the more I look at geomorphology the more I realise I have no real clue!

I did find one blog post saying that a similar looking thing might be caused by running water swirling around causing minor hollows to form in which iron rich stuff was deposited. With time/etc it formed into harder rock, the base rock being later eroded more quickly than the deposits. Sounds a bit far fetched to me.

Have you seen this on the ridge between Blea Rigg and Silver How?


By Lancashire Lad on 29/10/16 at 12:21pm

Hi Beth,

No, I've not seen that. - Will have to keep my eyes open when I'm next in that vicinity!

My best guesses for my "protrusions" are: -

Vesicles (gas bubbles in solidified magma) that have, over time, been filled with some material that has itself turned to solid rock, and which is harder than the original solidified magma. (I understand that such things are termed "amygdales" by geologists.

My second guess is "lapilli" of which there are several types (not sure if accretionary lapilli might fit the bill here), which can apparently be caused during volcanic activity when tiny fragments of magma are "exploded" up into the air, solidify, and then fall back into cooling areas of magma, which is not quite hot enough to re-melt them. So when the whole lot cools, they are retained within the overall volcanic rock formation as individual rounded structures. Although, if that were the case for these, (and if they are formed from exactly the same material as the main rocks), then I don't understand why they would not have eroded away at exactly the same rate as their surrounding rock.

Probably, both of my guesses will be poles apart from what these actually are. :oops:

Hopefully, someone might come back with an answer. (I have asked the same question of the Cumberland Geological Society too).

Regards, Mike.


By beth on 30/10/16 at 7:45pm

Over on the Facebook thread about this - https://www.facebook.com/WalkLakes/post ... 6065168280

Tom Lindley Hi - we also saw these. I think they are Lapilli. My wife noticed these as we were walking around Scarfell Pike - and as we walked we were walkking over an array of purpclastics off the Borrowdale Volcanic Series. If you unravel the "scene" the matrix is definetly ash and youcan see a "grain" as it was deposted. Also you can see the grain with the regular "nodules£. The nodules are quite regular and are green in collour and crystalline. I think they are olivines which are characteristic of a basic (silican deficient magma) which grew uninhibited in the hot magma and then erupted and became stratified as they cooled through the ancient environemtn - being laid down regularlry in the ash. Very interesting. That is what I think - dragging up igneous petrology I studdied at Kings College - London. All the best - Tom.

So you are probably on to something with the lapili.


By Lancashire Lad on 31/10/16 at 1:17pm

Thanks Beth (and Tom!).

I can't thank Tom directly via Facebook. I'm not yet converted to "social media", so am not registered with the likes of Facebook and Twitter etc.

That certainly sounds like a plausible explanation.

I did notice some layering (which I tend to associate with sedimentation) within rocks along that route. (Example can be seen on the boulders in the sixth photo down - *Looking towards Lingmell from the Corridor Route", in my Scafell Pike from Langdale walk report: - viewtopic.php?f=2&t=433 ).

I did wonder as to the origins of those, but hadn't thought of stratified layers of ash.

Regards, Mike.



WalkLakes recognises that hill walking, or walking in the mountains, is an activity with a danger of personal injury or death.
Participants in these activities should be aware of and accept these risks and be responsible for their own actions.