Letters from Aldwin

Ol Doinyo Lengai, in Tanzania's Natron Rift, rose four millimetres over eighteen months. Seven ground stations measured it. That is smaller than a satellite can see, and you would not have felt it standing there.

The rock lifted because something moved below. The best fit puts it three kilometres down; the honest range is one to five. No one could say how close it was, or whether it would come through. It didn't. The ground just stayed higher, and people kept walking on it.

Another study found the same summit sinking about three and a half centimetres a year for a decade. Two motions, one system, still going.

Most of what holds us moves like that. Under the surface, too small to notice, with no eruption to prove it happened. You can carry something enormous and never break through. That doesn't mean nothing is moving.

If you have been rising quietly under a surface no one watches, that is not nothing. It is only unmeasured.