Over long enough time, coincidences add up. A freak accident, a one-in-a-billion chance, can occur eventually - especially once the Laws are no longer being enforced quite so strictly, in the places far away from shining light.
Correspondence-engraved artefacts rest in ancient ruins, and the craggy cliffs are sometimes shot through with crystallized time. Cantankeri consume the Hours, breaking apart the stone to get at them. A freak accident aboard an engine results in a series of artefacts being lost overboard - the captain judges it better not to turn back. The things were unnerving anyway.
But when the artefacts land on a concentration of time, one that just so happens to be slightly fraying at the edges, the sigils interact and begin unspooling the power they're now exposed to. More and more, a chain reaction, a chaotic conflagration of noise and light and times past and future all brought into being at once -
And when the light and noise fades, things from distant places and times are littered about the now-cratered cliffside, explosions and rumbling echoing through the towering dark crags above, below, and around. Things, and a person.