Recommendations for exciting "geology" underwater?

[karlimmergut]

For someone who is not that much of a fish nerd, and does not get too excited about 3mm-long creatures that require a camera to fully appreciate, what's there to see underwater? Can you recommend any dive destinations with fascinating "geology" accessible to a recreational diver? Things like large pinnacles, walls that extend into the abyss, lava tubes, anything that is grand, monumental, and ancient, takes millions of years to form into the shape it is in today, and makes you feel small and irrelevant...

[EastEndDiver]

Every time I enter the ocean I feel small and irrelevant.

[randy88k5]

You can dive between the tectonic plates near iceland

Silfra - Thingvellir National Park, Iceland - Diving between Continents

[kierentec]

caves

[karlimmergut]

@kierentec: Is there any cave you could recommend that one could reasonably safely attempt without a full cave training? I have always assumed caves are the most hardcore specialty accessible only to tech divers...

[Doc]

The Galapagos allows you to dive within the remnants of volcanic cones.

On Roatan, along the South shore, you can see certain sections of vertical wall that were dislodged by an earthquake. These areas are much more interesting after repeat visits over a period of time as they change with inhabitants daily. Within hours of the incident, Banded Coral Shrimp appeared.

totse.com | Underwater Pyramids in the Bahamas

DROWNED CITIES

I would encourage you to reconsider looking at little critters. You can have a real education with a cheap glass magnifier and a flashlight. You've swum by a million of them, and there aren't all that many geographic structures easily available to the recreational traveller.

[Fish-R-Man]

Palancar Caves - Cozumel (not true caves)

[eponym]

The sheer cliffs and overhangs of finely fractured basalt in Crater Lake, Oregon. Hike your gear down the Cleetwood trail, dive to the right of the boat pier. This is an altitude dive (6200 fasl) and cold, but with great viz. The stone landscape is as impressive as anywhere else I've been on this planet.

Another geologically unique destination is the Seychelles, which are granitic, very unlike the usual volcanic island reef systems. The granite splits into large smooth surfaces, and at times it's as though you're swimming between two four-story buildings.

As to feeling deep time, Crater Lake was formed about 5000 years ago, within the memory of local tribes. And the the Seychelles are shards of the African continent that drifted off some millions of years ago along with Madagascar.

Very exciting, on a deep time scale.

[Fish-R-Man]

Cavern dives in the Riviera Maya zone south of Cancun. Dos Ojos is a good one to start. Coming out of the dark sections into the light on a bright day is assume!

[Guba]

The Flower Garden Banks NMS (110 miles off the Texas/Louisiana shore) are actually the tops of three salt domes that have risen and pressed to within about 80 feet of the surface. Flower Garden East has an impressive wall structure that does, indeed, fall away toward the benthic flats about 350 feet below. The majority of FG East and FG West is covered by huge coral heads. However, Stetson Banks (also part of the NMS) about 15 miles toward shore reveals inclined strata largely made of siltstone. The layers of sedimentary rock have "weathered" into lines of cracks and crevices and are sometimes described as a "moonscape", though I personally think it's a bad analogy. Perhaps folks are just trying to emphasize that Stetson Banks is radically different from other dive destinations they have experienced.
Not an item of natural geology yet very striking is a dive on gas production platform "High Island 389", located in the corner of the NMS. Because it's within the borders of the sanctuary, the legs of this platform are "cleaned" less than on other platforms. The result is a striking artificial reef system that extends from nearly the surface down to...well, darkness. It's extremely visually interesting to dive the huge legs of this platform and see them just disappear into the 450 foot depths. By the way, vis in the FGBNMS typically runs 100+ during the summer.

just my two cents...