Let's see what this volatile lot will do with this one.

A tectonic plate? *a low approving approving murmur rises from the audience* No
Molten lava? *the audience passes around Damart catalogues as the ushers attempt to turn up the radiators* No
Mineral-laden hot springs *"We could use some of those here", think the audience* No

À la Lara Croft, he muses, with a silly grin.

A continental shelf? *the audience muses on the fact that there are about 21,500 Google hits for "Lara Croft" and "the answer"* No
Magma? No
Tsunami? *the audience seeks diversion in a spirited discussion of the correct plural of 'tsunami'* No
An earthquake? No
A glacier? No
An iceberg *the audience nods knowingly at the ironic appropriateness of Chalky and irach's moves*

Looking back, I may have mis-directed people with the answer to the solid question. Perhaps a better answer would be "Yes, partly."
Do we want a clue?

Antarctica? *the audience sits up straight, puts away their papers, Sudoku puzzles and knitting* No, but in some ways the closest answer yet

[irach] that's TWO guesses - very naughty!

[Chalky] Nothing wrong with irach's question -- it has a yes-or-no answer, and if the answer were yes, then it would simply be all fingers on the buzzers to guess which one!
Oh, and if I am right, I hereby transfer my win to irach.

The ocean? No
The North or South Pole? *the audience giggle quietly* No
The Arctic Ocean? No

I'm with CdM on irach's question - people do bend the one-question rule (me included), and a single question can anyway turn into a mutiple answer (see "terrestial object" above).

Chalky has now got the geographically closest answer, but in other, more important ways, irach is still closest.

I am going away this afternoon, and work means I'm unlikely to be able to play more than once again before I go. Any volunteers to take over as quizmaster/mistress? Email me at pubsalesatbaafdotorgdotuk .