Campfire physics: the role of the rock circle

Confession: I’m not an experienced camper, just an enthusiastic novice

I camped in a lovely place this weekend and our campsite had a ready-made firepit complete with a one foot high (approx) circle of large rocks around it.

Prior to this trip, I’d assumed the sole purpose of the rock circle was to confine the fire, making it safer. Several observation from this weekend have me adding other, equally important functions for the rock circle.

The evening was cool (low 50’s) and a mild breeze blew. The fire started easily with a few scraps of paper and twigs. The addition of slightly larger sticks, however, resulted in extinguishment. Undeterred, my camping savvy GF re-lit the thing. This time, more cautious with additions (real meaning-forbidding me to smother the fire), slowly she built it up.

Within 15 minutes or so the campfire blazed. The flames attained a height of 1-2 feet (high enough, but with a margin of safety, my GF assured). Nevertheless, unless I was nearly on top of the fire, or in the path of the smoke, it didn’t feel very warm. Furthermore, our difficulties maintaining a roaring blaze continued for an hour or so.

At this point, without an increase in flame intensity, the campfire gradually became warmer from our vantage. Additionally, logs added to the fire ignited easily and save for the addition of logs by us, the campfire became self-sustaining. Concurrently, I noticed that the rocks in the rock circle were hot.

Was the absorption and re-radiation of heat by the rock circle contributing to these changes? The geometry is perfect to focus thermal radiation toward the center of the circle. Might this have a catalytic effect? I considered also that the embers may play a role though I’m unsure of the magnitude of the contribution.

Any thoughts? Any observations from un-rock circled campfires?

The purpose of the rocks is to prevent the smoke from following you around, no matter where you sit. If this doesn’t work, you need to turn the rocks with a left-handed Smoke Shifter™. If you don’t have one, ask at the next campsite, they probably have one…

The rocks keep the screamapillars at bay.

Fear Itself nailed it, although he left out the brand name. There’s only one truly reputable manufacturer of a Smoke Shifter, and you’d truly be loath to use one by anyone else. Get thee to thy neighbor’s campsite and ask for a Orgasmic Smoke Shifter.

If they just stare at you, ask louder.

Accept no smokestituskies.

You’ve got most of the right guesses. It’s heat reflectivity and refractory substances.

How big of a diameter?

The location of the fire circle was probably to locate the blaze nowhere near any readily combustible materials.

I tend to use the Sunday NY Times approach. Wood needs to carbonize before it can burn. So I use lots of paper to jump-start the process. I use split-up framing lumber scraps as kindling and when that starts to burn I can add bigger wood.

I’d say you got the rocks and surrounding earth nice and hot. All that stuff is radiating in IR intensely. Most of my fires are burned in a Franklin stove. One Christmas Party my brother came down to start a fire for the party. He must have been channeling Sacajewea or something becuase he had a little pile of twigs on the grate. After a half an hour or so watching his ineffectivenss I threw on I chucked in dome scrap lumber and newspaper.

Absolutely, withot the catalytic effect, however. Catalysis usually refers to the chemical enabling of reaction. The thermal feedback from the surroundings is accelarting rather than enabling, per se, the combustion.

The following is a list of indispensible camping items, none of which were at hand for my weekend trip:

A Long Weight (Wait)
a long stand (similar to your long weight)
A Left-Handed Fish Slice
A left handed mallet
A glass hammer
A bubble for a compass / spirit level
A Rope lengthener
A self emptying billy can
A blunt point
Second Aid Kit (bit like a First Aid Kit but used afer the bandage has been put on)
sparks for the camp fire - requiring a damp paper bag to carry them in
bacon stretcher
200 ft.of shore line.
Dehydrated water
Tins of frozen carrots
Tarten Paint (to identify the tent poles).

Smoke shifters don’t make MY list. :slight_smile:

Someone address the OP, PLEASE.

OK somebody addressed the OP. Sorry, wasn’t using catalysis in the strict chemical sense. You get the idea though

Back when I was active in Camp Fire Girls, they told us that the stone circle was a marker. We weren’t supposed to place or store anything flammable inside that circle, except fire materials as we were adding them. ANYTHING ELSE that was flammable was supposed to be carried or worn (foodstuffs about to be cooked, clothing that was worn, etc.).

I think that the rock circles got started as a way to mark the hearth area. The fact that stone will absorb and then radiate heat is just a nice little benefit. You have to have SOME way of marking the fire area, and you need to do it with a nonflammable material. Stone is about the only nonflammable material that’s handy in a campsite. I mean, glass, metal, things of that nature just aren’t real prevalent in most camping areas.

A campfire is the wilderness TV, offering quality content, but with no commercials.

Well, I’d start to have questions regarding infernal spiritual motivations if one started building pentagonal fire pits. That aside, a circle is the most efficient use of materials in the perimeter to area ratio, so, it makes sense that way.

A tall-ish wall of non-combustible material also makes sense to contain the fire. You wouldn’t want a wind to blow sparks and hot embers everywhere. Out in the wild, you can use rock or… rock. Your choice.

A tall-ish wall also creates a chimney effect. Heat is forced to go straight up, creating a draft drawing in air at the bottom. This draft keeps a steady source of air coming in for hotter combustion. It exhausts the smoke over the head of the people seated around the fire.

And yes, the rocks retain and irradiate heat, creating a more even outward flow of heat and providing heat even when the fire burns down while sleeping.

(A side note: I constantly scream at the TV when watching Survivor and seeing the ‘cast’ create the worse campfires imaginable. Without the wall, one guy fell in and burned his face. Without the wall, they had sparks landing on them while they tried to sleep at night – they had the fire right next to their sleeping quarters to stay warm at night. Without the wall, rains easily put their fires out. These dummies create elaborate shelters but they can’t collect rocks to contain their fires.)


[safety tip] Please do not collect stones for campfire rings from streambeds or other places where they might have soaked. Heat + H2O trapped in stone=exploding rocks. [/safety tip].

More dangers of dihydrogen monoxide…

When are they ever going to come to their senses and outlaw that stuff, anyway?

No sky hooks?

Safety tip no. 2: Do not try to get a smoldering campfire going again by pouring just a little bit of Coleman fuel on it. the fire will re-light, so will your hand, it will hurt.

If it doesn’t travel up to the can, which might explode.

I thought the main 2 reasons is to desiginate a fire area, and to create a wall that would stop wood from ‘falling/rolling’ out of the fire area as is it shifted due to pieces burning away that supported it or by a person adding a piece, poking the fire, or trying to jump over it after one consumes one too many beers.

The reason for stone is because it it available on site, last a really really long time, allows some air infiltration, cost nothing. The effects of the re-radiating of heat was just a side benifit.

ALL my humble O

While you’re right that the morons on Survivor obviously cannot build or maintain a fire … since most seasons are filmed in a beach setting, I imagine it would be pretty difficult to find big-ass rocks to surround your fire pit on a sandy beach. Last time I went to the beach, I didn’t see any. They might be able to find big chunks of dead coral in the water, but knowing Survivor contestants, they’d kill some live coral instead. Or try to use big seashells or something.

I’m going to the beach again soon. I’ll look for some big rocks.

Forgot relative bearing grease to keep your compass in good trim, too…

From my younger days…my observation is that a fire doesn’t really ‘put out the heat’ until it has an amount of glowing embers under it. Even if the fire dies down, the embers underneath still put out the heat for a time.

I love sitting by a campfire late into the night, watching the embers glow, occasionally poking them with a stick to spread them out or push them into a pile.

The last time I did this, it occurred to me that my ancesters have been doing this for about a hundred thousand years or so. A comforting thought.

Or perhaps not… have we really evolved to mindlessly stare at the TV of an evening?
If someone shows up to nitpick that it’s only been twenty thousand years or whatever, I can only say “get a life”.