North America Is Dripping from Below, Geoscientists Discover | Hacker News Reader

North America Is Dripping from Below, Geoscientists Discover

jsg.utexas.edu

144 pointsjandrewrogers36 comments

> Researchers have discovered that the underside of the North American continent is dripping away in blobs of rock — and that the remnants of a tectonic plate sinking in the Earth’s mantle may be the reason why.

Really appreciate the first sentence of the article having a pithy summary of what the whole thing is all about.

Yes, thesis statements are very useful, especially in the Internet age when we are overloaded with potentially interesting things to read. Unless I already believe you have something essential, I generally won't follow you on your mystery tour.

Maybe that reduces audience engagement time.

That headline feels like a really clever metaphor for something but I can't figure out what.

it reminds me of how in San Jose, CA, there are several roads that were constructed below the local water table. so effectively there’s always water bubbling/“dripping from below” and causing puddles and erosion.

That which is good and right is built on deep foundations which are often forgotten or neglected in favor of surface level activity.

Related: it's like the "Everything is fine" meme cartoon picture, except the people seeing the scene unfold are forbidden from talking about fire.

Article is dated April 1 but the actual paper is dated March 23.

Sometimes it can be hard to tell when it's outside of your domain.

or an april fool's joke!

Is there any possible justification for using the word "dripping" rather a normal word like "sinking"?

To me, dripping requires liquid drops that travel through air or a vacuum. Maybe through another liquid if the drops cohere. But solids can't drip, and substances can sink or travel or migrate through a solid but they can't drip through it.

Is there some special geological meaning of "dripping"? Or is this just bad English?

It's called "mantle drip" or "lithospheric drip" in the technical literature. "Lithospheric mantle delamination" is a more descriptive variant. We're fond of fun terms in geology. E.g. the "jelly sandwich model" vs the "creme brulee model" for lithospheric strength is closely related to what's being discussed here. And yes, those are the proper technical terms.

Solids can indeed "drip". The mantle is a solid, but it still very much flows. "Fluid" means no shear strength, but fluids are not the only things that flow and flowing is separate from having a shear strength. Fluids do not behave elastically. If you stress them at all, they permanently deform. Elastic materials behave like a spring up until a point. When you stress them, they deform, but will pop back. The mantle is viscoelastic. Strain rate matters in how it deforms. When you stress at high strain rates it, it deforms, but pops back (i.e. shear waves from earthquakes can pass through). If you maintain those stresses at a low strain rate, it will slowly permanently deform. That's, by definition, flow.

This is a good analogy for what's being discussed: https://en.wikipedia.org/wiki/Pitch_drop_experiment

The reason "mantle drip" is used is to evoke a mental image similar to that experiment.

Thank you!

Still seems a little weird to include in an article meant for a general audience, but I appreciate that geology uses these as technical terms.

Since you know the field, can you explain what the difference is between a solid flowing and a solid dripping? Thinking about it more, my mental model of dripping requires surface tension for drops to even exist. But surface tension doesn't exist for solids, right? What defines a solid "drop" as opposed to, I don't know, just a layer or pieces?

Or am I overthinking this and it was just chosen as a silly fun word to use?

Rock behaves like warm wax on geologic timescales. Kinda crazy..

Was hoping to find a source to back up my memory on this,FWIW, Google's AI summary states it well:

> On geological timescales (millions to billions of years), rocks, even those that seem brittle, can deform plastically, or flow like wax, due to the immense pressures and temperatures deep within the Earth, allowing for slow, gradual deformation

I believe it's a shame that the drippings do not create the basis of a mantle-stalagmite. That would be a neat feature to study.

'Our continent keeps on dripping, dripping, dripping, into the mantle...'

Doo-doo dah doo-doo.

---

Is there currently any type of ground penetrating radar or other device which could physically confirm the model's output?

It is not just model output. The paper uses seismic tomography to image it:

https://www.nature.com/articles/s41561-025-01671-x

The abstract mentions:

> Here we present a full-waveform seismic tomographic model

So presumably, you would actually do the seismic tomography (if they haven't already). Instead of radar, you use the waves from earthquakes!

it usually starts with a stalactite, then a stalagmite; by the way is there a mnemonic for the two words in English? something like t for tumbling and m for mounting...

I always remember it with “g” for ground and “c” for ceiling… haha but I do like the mites and tites one too in a neighbor comment :)

The one I've heard is 'just remember ants in pants: the mites go up, the tites come down'

Stalactites hold “tight” to the ceiling.

Courtesy of a 30-year-old Bill Nye episode.

I also heard this lame one: stalagmites might hang, but they don't.

I memorized it as "c" for "ceiling" and "g" for "ground."

If I needed a mnemonic today, just remember that drops slowly drip from stalactites, like drops in a chemical titration procedure.

Tights go down and mites go up.

T from the top

hope it holds tight...

Steve Miller song at the speed of continental drift.

This makes a lot more sense to me as to the origin of the Great Lakes, opposed to the common explanation that the extremely sharp and deep lakes were carved by glaciers, which one would expect to be very shallow instead

I think the formation of the Lakes by glaciers was substantially different to glacial action we see today. It's commonly accepted that the Lakes were formed by the existence of the Laurentide ice sheet which was up to _2 miles_ thick in places - that's vastly different to the glaciers we see today and the effects that they have had.

While the idea that they filled up from below may make more intuitive sense at face value, the "common explanation" in this instance is substantiated in many different ways and doesn't seem far fetched when you study it a little further.

There's something fascinating about knowing that there's movement happening hundreds of miles beneath our feet.

Its happening right beneath our feet too! Go dig up the rocks in your yard, come back a year later, and you will find it's full of rocks again.

Phrasing!

Also figuratively.

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