Strong and sturdy as bedrock may seem, it’s possible to pile enough weight onto the Earth’s surface to squish it downward a bit. The planet’s great ice sheets, for example, have done this on a pretty significant scale. Many regions that are now relieved of the ice sheets they hosted during the last ice age are, in fact, still slowly rebounding upward today.

The coverage of modern, sensitive GPS networks allows us to see subtler versions of this process playing out even over the annual cycle of wet and dry seasons. And these networks may have caught Hurricane Harvey’s record-setting rainfall depressing Earth’s crust just a little.

On Monday, Jet Propulsion Laboratory researcher Chris Milliner posted a plot of the change in GPS station elevation immediately after Harvey. The data showed that the Houston landscape had sunk as much as two centimeters. While that’s not enough to worsen flooding that was measured in (many) feet, it’s actually quite impressive for a sudden change from a single weather event. That’s a testament to the weight of the preposterous amount of water the area was under.

Milliner told Ars that this change is a bit larger than the seasonal cycle there—but it occurred over just a few days—so it’s outside the range of “noise” in measurement-to-measurement variation. Normally, a short time period like this would yield a random mix of slight ups and downs rather than a coherent signal.

This is likely the result of the rock beneath the Houston area compressing a tiny bit under the weight of flood water, which would mean it should pop back up a couple centimeters in short order. But it’s possible that some of the drop is due to sediment compacting more densely—a change that doesn’t necessarily see a rebound.

Houston knows all about losing elevation to sediment compaction, because it also happens when you over-exploit groundwater aquifers. If you go back to the 1920s, some localized spots have lost ten feet of elevation as a result of this process.

Milliner plans to apply a more detailed analysis to the GPS data to get a clearer picture and see how closely the depression-and-rebound pattern corresponds to the rise and fall of Houston’s floodwater. For now, it’s just remarkable that we saw anything at all.