The crust and uppermost mantle of a area in the Great Basin has sunk into the more fluid upper mantle beneath the Great Basin [right, credit J.D. West, Silverheels Photography] and formed a 100 km wide, 500 km tall cylindrical blob of cold material far below the surface of central Nevada, according to an article published this week in Nature Geoscience by a team of geologists led by ASU student John West and professor Matt Fouch.
The title and news release about the paper offered an evocative description of the blob 'dripping' into the mantle. The story is zooming around the web, with all the science news reporting services featuring it and the geoblogosphere diving in.
Matt Fouch is quoted as saying "lithospheric drips—sinking plumes of cold and dense lithosphere—are relatively small and transient features." Cheryl Dybas, my favorite science writer at NSF, described it thusly, "A lithospheric drip can be envisioned as honey dripping off a spoon, where an initial lithospheric blob is followed by a long tail of material."
Apparently there's been some hot discussion in recent years about the whole concept with Matt expressing doubt (solidly "anti-drip") until this new evidence came via seismic tomography, using results from the USArray deployment of broadband seismometers across the West over the past few years.
Nature Geoscience
Published online: 24 May 2009 | doi:10.1038/ngeo526
Vertical mantle flow associated with a lithospheric drip beneath the Great Basin
John D. West, Matthew J. Fouch, Jeffrey B. Roth & Linda T. Elkins-Tanton