How Did I Explode A Saucepan?

I work in a commercial kitchen and I've seen this happen before, which is why we do not use copper-plated cookware. This can happen whenever you have two different alloys welded together and apply heat to one side or non-uniformly; An effect known as 'thermal shock'. What happens is one metal expands faster than the other, causing a deformation or fracture. Think of it as one side trying to 'pull' the other at the edges. The pop you heard was undoubtedly this delineation occurring, followed by the kinetic reaction of the pot jumping.

I find your claim that the pot leaped through the air difficult to believe, but I have observed audible pops and visible movement when they fail. If you have a flat top (like an electric stove), it could skid for up to a foot from this due to the lack of friction and possible presence of condensate (water) on the surface which can at certain temperatures act like a nearly friction-less cushion. Oil doesn't do this, only water.

If you've ever been in a commercial kitchen you'll notice every cookware item is made of a single cast of metal (most usually stainless steel) because of this. Welded alloy pots and pans just don't last very long -- the effect observed so violently happens at a smaller scale with every heating cycle, eventually resulting in ruined cookware. Also, being a line cook means being exposed to things exploding, dying, catching fire, etc., on a near-daily basis, not to mention an assortment of knives that would make most Hollywood bad-asses blush, so obviously we try to limit the number of things that can go wrong.

Do yourself a favor -- if you stick with the copper-bottomed pots and pans, make sure to put plenty of water or oil in them. Heat with nowhere to go will cause failure quickly.

(if I understand correctly)

You probably used a cheap and very thin saucepan, and on the heat the metal expanded and had stressed to the point of failure, it buckled and acted as a spring.

If your electric hob is anything like the one I had when I was younger, it has small rings in the metal of the hob top.

If the pan was wet, the water can pool there and become superheated, until the weight of the pan isn't enough to contain the force of the expanding steam. At this point, the pan jumps, pushed upwards by the steam. If the pan is cheap or old, the force of the jolt might be enough to break it.

My pans used to dance on the hob when wet, as the steam let off in small amounts all around the hob. After a few minutes, the water would be gone and the pan would sit normally.

I've seen similar things happen with the flat kind of electric hob with the little hollow in (this kind: https://commons.wikimedia.org/wiki/File:Electric_stove.jpg )

This can happen when the stove is wet. If there is water in the hollow when you put your pot on it, and the flat bottom of the pot closes the cavity, the water underneath will start to boil. If the stove/bottom of the pan is also oily, it can stick to the stove.

When the water in the cavity starts to boil, it will rapidly expand. With nowhere to go, it's possible for a pot to go flying when that happens. This is not, as you already had a gut feeling about, supposed to happen.

If it does happen though: Don't catch it. The best thing that comes from that is that you can say "hey, did you see that, I caught it". More likely scenarios involve burning yourself or cutting off fingers (for knives).

When things fly through the air, it's likely you're going to have to clean the floor even if you catch it.

Not so much "plate tectonics" but "pot and pan tectonics". This is likely a manufacturing defect. The thermal expansion answers are correct, a sudden shock occurred when a "critical point" was reached and the base has sprung back into its "relieved" state. (I do not think there would have been enough heat for annealing to be a factor.)

As for super-heating, water will "knock" if superheated and detergent is added (or any surface active agent). But normally ceramics or stoneware is involved (something with vertices).

There are many companies which produce glassware that is safe for the oven. Although many of these products resemble sauce pans or skillets, they really are casseroles for use in the oven. If you place them on an electric eye or a gas flame, within a minute they will explode into tiny fragments, usually leaving the handle behind.

I had purchased a rather expensive version of these some years back and my roommate did this, not once, but at least 3 times, ignoring the large embossed letters on the pan: "NOT FOR STOVETOP USE"

yes this can happen, its caused from the saucepan being placed into cold water over time, the sudden temperature change from very hot to cold causes decontamination (the saucepan to heat sink / copper base ) partially separating allowing water to enter, once the saucepan is heated again the trapped water turns into steam increasing its volume by 1000 and going off like a bomb.