With torrential rains preceding and following our drop below freezing temperatures, I observed a strange series of ice formations right outside my patio.  These ice spikes grew upward from the ground.  My first assumption was that they were precisely that: ice spikes (a.k.a. ice fountains), a very natural formation caused by a thin layer of ice with a weak spot where liquid water is forced up and out, after which it freezes, and the process creates a literal spike of ice that continues to grow until its tip finally freezes (at which point no additional water can be forced through it).  It would be safe to assume that’s what I saw considering the ground was drenched by heavy rains before it froze, so the freezing water in the soil continued to push liquid water up through weaknesses that formed spikes.

But I don’t think that’s what happened in all cases.  So I thought of another theory.

Similar to an ice spike but via a different mechanism (solid rather than liquid), a bit of ice formed in the soil.  Then, as the liquid water in the ground continued to freeze, and therefore expand, it pushed a growing column of ice up through weak spots in the surface.  This would be the same mechanism as an ice spike except that, in this case, it was solid ice that was forcing its way upward into a growing column rather than liquid water rising through a tunnel of ice and later freezing.

But I don’t think that explains everything either.  I actually suspect the frozen spires and odd shapes formed by various mechanisms.  The reason I say that is because they came in all sorts of shapes, and at least half of them formed on top of rocks on the surface.  Take this photo for example:

You’ll notice immediately that the large spike rests atop a stone.  Its base is hidden somewhat by a few other chunks of ice in the foreground (and out of focus), but it should be easy to identify the rock underneath the spire by looking around the fuzzy obstacles.

If you look at the one on the right that has been pushed out of the ground, it too formed atop a stone (probably a chunk of limestone given its color).  Because the stone’s hue is nearly identical to that of the ice, and because the soil stuck to both melds them together, it’s a bit more difficult to see the rock on that one—but not impossible.

So what makes such formations take shape on top of rocks?  An ice fountain can not form on stone.  A chunk of ice forming in the topsoil and being pushed upward by additional freezing beneath it likewise will not form atop a stone.  With those two options negated, I pondered what process could be responsible for such ice formations.

You’ll notice it shows on the far left a spike pushing up through the ground.  It’s covered in dirt and is just below the large chunk of ice that undoubtedly grabbed your attention.  The one coming through the soil is probably a formation caused by expansion of ice in the soil (not necessarily a spike or fountain in the true sense).

The large one above it, however, formed on top of a rock.  And as you pan across the photo, you’ll notice a mix of them—both from the soil and atop a stone.

In fact, near the center of the image is a stone that appears to be floating in the air.  It’s actually stuck in the top of the spike beneath it that has pushed up through the ground.

Further to the right is a curved spike.  That one really boggles the mind.  It too formed on top of a rock, but I can’t come up with a good reason for its shape.  I might have said it formed from a curved hole in the ground which manipulated it as it formed, but that wouldn’t explain the rock.

So, I’m again left with the quandary: I’m comfortable with the process that forms spikes and projections directly from the soil, but what process is responsible for ice spires that seem to grow on top of stones?

Ah, I do have a theory just as you’d suspect, although it doesn’t fit all the evidence and may be entirely wrong (especially when one considers that curved marvel in the second photo).

Here’s what I think: As with the air, wet soil takes longer to heat and cool than does dry soil (humidity reduces the efficiency of thermodynamics).  That means, after all the heavy rain preceding the freeze, the dirt itself would stay above freezing longer because it was saturated.  On the other hand, stones would not absorb that level of moisture and would freeze more quickly than the ground around them, especially those sitting on the surface rather than partially buried.  Given that the stones would reach freezing sooner than the ground, the freezing rain we had would stick to them first—but only to the surface of the stones and not the ground around them.  That means ice would form atop the rocks in growing towers as rain fell from above.  Essentially, the same process that forms stalagmites in caves is probably responsible for forming these ice structures on top of the rocks.  Since only the rocks could support ice formation at the time, that’s the only place the water froze, so it piled up into these little towers.

One thing that supports this premise is in the second photo.  If you look closely in the top-left section just to the right of the large chunk of ice, you’ll see a large stone that is partially glazed with ice.  Protruding upward from the glaze appears to be the beginning of an ice spike.  (It is partially out of focus, so you’ll have to look carefully).

I’m left with a satisfactory explanation for the majority of the structures.  Ice spikes (fountains) explain some, surface ice projections explain others, and ice stalagmites on the rocks explain even more.  That said, there’s still that curved number, and a smaller one above and to the right of it, which don’t seem to fit any of the explanations, at least as far as I know.  But I’m not an ice expert although the physics of the processes is definitely my forte.  That leaves me with one unanswered question that likely I’ve already answered: The curved ice probably formed as a spike or projection, but its foundation grew in a confined space that meant it had to curve in order to expand.  Or the ice began forming but became top-heavy, so it slowly tilted to one side as more ice formed (although that doesn’t explain it half as well).  Or something else…