The Fulgurite Thread

Hey so I've been both a climber and geologist for over 45 years and only over the last three or four have I become aware of rock fulgurites -- visible "scars" on the rock that are the result of lightning strikes.  The scars represent localized surface melting of the rock that look like a glaze not unlike a frosting on a cake.   Now that I am tuned into them, I have some thoughts.  I was hoping for this thread to be a repository for some good pictures of rock fulgurites in different settings.

I know that some of you know about them.  After all, there is a climbing wall in Wyoming called the Fulgurite Wall (I looked, and yes, for sure they are fulgurites).  The 8 snapshots below are from a location near Mount Evans, and I purposely chose these because of the relationship between orange lichen and fulgurite, a subtopic.

This is awesome!  I have noticed a bad and funny smell which seems to go hand in hand with these granitic fulgurites, does anyone know what that is?  

As to the orange lichen, could that be because these fulgurites seep some specific mineral or nutrient that the orange lichen like?  

Also, anyone know why they often form in caves?  How does the lightning get into the caves?  Greg?  Anyone?

Not Hobo Greg wrote:

How far into caves? 

Typically 5' or so, but as much as 20', or even 30'. Sometimes 40'+.

Typical texture of a fulgurite in the Mount Evans area

And how about this bad boy!  It looks like thick frosting or paint.  These are clearly flow structures. The edge melted and flowed down.  Notice also how the left side of the fulgurite looks like a coastline.  That's because the white part was liquid.

Not Hobo Greg wrote:

Oh nice!! I only learned about these this past summer but now I see em all over. Scary too because lots of em are nowhere near a summit but hundreds of feet below one. I’d like to know what it is that attracts the orange lichen. Whatever species of lichen it is, it grows elsewhere too, but the only lichens I’ve seen surrounding the scars are the orange ones.

Maybe nitrogen fixed during the strike that gets trapped in the glass?

I've run into a few of these while in CA climbing, thought it was bird shit at first, but ended up being this glass like substance. 

Thanks for putting a name to it Greg. 

Love me some fulgurites! Did a route once called Farming Fulgurites.

This thread is cool. I’m going to keep my eyes out and see if I can find any. Do they take on significantly different appearances in different rock types? Your pictures all look granite-esque. Are there examples on basalt/limestone/sandstone/quartzite/others? 

JNE wrote:

Typically 5' or so, but as much as 20', or even 30'. Sometimes 40'+.

Caves often act like the gap between spark plug electrodes.  Basically the fulgarite in a cave is the result of the subsequent arc across the gap after a charge release, not a direct strike.   Another good reason, like Greg mentioned, to not seek shelter in them unless you are able to go way deep, but biggest risk is in the 0-10 foot range of the mouth

JNE wrote:

This is awesome!  I have noticed a bad and funny smell which seems to go hand in hand with these granitic fulgurites, does anyone know what that is?  

As to the orange lichen, could that be because these fulgurites seep some specific mineral or nutrient that the orange lichen like?  

Also, anyone know why they often form in caves?  How does the lightning get into the caves?  Greg?  Anyone?

I'm wondering if these fulgurite look a lot like pack rat urine deposits (or bat urine?). I have seen a lot of "things" that look like the fulgurites example above in Vedauwoo, but was told it was from pack rats. The smelly ones would be in caves and overhanging areas - reinforcing the urine deposits. I have heard of lightning jumping the gap in caves, so not eliminating the fulgurite.

Peter Carlson wrote:

Maybe nitrogen fixed during the strike that gets trapped in the glass?

Most likely answer. I listened to a podcast recently about a researcher looking into lightning strikes on otherwise dead soils, and found they were rich in bioavailable nitrogen. 

Here's a couple of what I am sure are fulgurites from Vedauwoo.  It's those white streaks.  They represent where the lightning arced across the gap, forming the fulgurite and, because of gravity, the melt flows down a bit.  A year ago I would have assumed that these were some kind of bird poop. 

I definitely referred to these as petrified bird poop before I knew what they were.

So, here's a picture of a small tower at around 12,500 feet where there are no pissing rats (or bats) and no roosting birds.  Fulgurites in this environment tend to occur underneath overhangs, within vertical crack systems, particularly chockstones within the cracks, and on the bottoms of small alcoves. Notice the similarities with the proposed Vedauwoo fulgurites.

Another example of fulgurite beneath overhang in an alpine environment.

That is cool stuff!

I’m on the lookout now

TFPU!

Super cool. I've seen these in the past, but never had any idea of what they were (except possibly bird poop).  Thanks for posting about this.

I always thought that was bird or bat shit.  Sometimes had mistaken them for a huge chalked jug from the ground.   Interesting. 

This is nuts. I 100% always thought this was raptor poop. I associated the smell with guano. Still not positive this isn't a troll thread.

Those look a little different than other rock fulgurites:

@bryan, the above are dacite and Cascades volcanic summits, the below are granite. Fulgurites have a very different appearance in sand/gravel/soil than bedrock strikes.

Here's a gabbro fulgurite:

In the Vedauwoo images I agree that it looks like there's gravity driven flow, but are you sure that isn't dissolution and reprecipitation of guano? It seems that the white spots are on a nice 'perch' location at the edge of a ledge or top of a boulder. Do you see them on overhangs or places where bird/rodent droppings wouldn't be deposited? Lichen correlation would also be compatible with nitrogen-rich bird shit, right?