There’s nothing better at the end of a hard day on the trail than sitting around a campfire. But if you have rocks in or around your campfire, then there is a risk that they could explode! So here are some tips on avoiding exploding rocks!
How dangerous are exploding rocks?
Well, they certainly sound pretty dangerous, but a rock in a fire will crack or pop most of the time and not actually explode. However, on rare occasions, they can explode with some force, sending splinters of rock and embers from the fire flying! This can cause injury or burn holes in clothing and equipment.
Why do rocks explode in campfires?
A rock can explode in a fire due to pressures that can build up inside the rock under heating. These pressures can be made more acute due to a few reasons, which will make an explosion more likely:
Moisture inside the rock
We all know the pressure that steam can produce; the exact same science can be happening inside the rock if there is moisture present. Even if a stone is dry on the outside, there can still be some water inside it. Some rocks are more porous than others, meaning they can absorb more water. For example, a porous rock such as sandstone will likely contain more water than a non-porous rock such as granite.
Rocks being heated too quickly from cold.
Sudden changes in temperature inside the rock can cause what is known as Thermal Stress. For example, when a cold rock is thrown into a fire, the sudden heat will cause the outer layers of the rock to expand while the middle of the rock remains cold. This difference causes pressure to build up, which can result in an explosion.
How to stop rocks from exploding in a campfire
Try and choose non-porous rocks which are less likely to contain moisture. This can be easier said than done, depending on the terrain that you’re in, but if you can, try and pick one of the following:
And avoid porous rocks such as:
The next tip is to look for rocks that are dry. For example, if it’s raining, look for rocks under the shelter of a tree or bolder. If a rock has moss growing on it, that’s a clear sign that it’s wet. If you are picking rocks around a river or on the beach, make sure they are well above the waterline so that they’ve had a chance to dry out.
Now that you’ve picked your rocks, it’s time to arrange them around the fire. It’s important to place the rocks before you light the fire so that they have a chance to warm up slowly. If you throw a cold rock into the middle of a raging fire, there’s a fair chance that it will explode!
Finally, there a reason why the archetypal campfire is always surrounded by a neat ring or nice round rocks. If a rock has a nice round shape, that’s a sign that it’s tough. It’s probably solid granite and has been bouncing around on a river bed for hundreds of years, so it’s more than likely to survive your little campfire!