Hmm, I'm using something different now. I never get volcanos+waterfalls on the same embark map btw, just the same region map. Although it seems like it should come up eventually, nothing to stop it, just need a massive alignment of the stars for worldgen to drop a volcano right on the edge of a mountain range then run a pair of rivers past it.
http://www.bay12forums.com/smf/index.php?topic=59969.msg1349430#msg1349430 has an old set of parameters although I don't think it's ideal.
New parameters, you might find them interesting still:
Created in DF v0.31.08.
[WORLD_GEN]
[TITLE:NEW]
[SEED:1007682789]
[HISTORY_SEED:2903508663]
[NAME_SEED:1055879430]
[CREATURE_SEED:2767106804]
[DIM:17:33]
[EMBARK_POINTS:1274]
[END_YEAR:1050]
[BEAST_END_YEAR:75:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:99:400:1500:3200]
[RAINFALL:0:100:100:100]
[TEMPERATURE:40:60:100:100]
[DRAINAGE:0:100:100:100]
[VOLCANISM:0:100:3200:3200]
[SAVAGERY:0:100:100:100]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:3:1:1:1:5:1]
[DRAINAGE_FREQUENCY:3:1:5:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:3:1:1:1:1:5]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[TITAN_NUMBER:1]
[TITAN_ATTACK_TRIGGER:80:0:100000]
[DEMON_NUMBER:20]
[GOOD_SQ_COUNTS:1:10:20]
[EVIL_SQ_COUNTS:3:30:60]
[PEAK_NUMBER_MIN:1]
[PARTIAL_OCEAN_EDGE_MIN:1]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:15]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:150]
[RIVER_MINS:20:20]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:0]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:100]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:50]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:3]
[CAVE_MIN_SIZE:3]
[CAVE_MAX_SIZE:5]
[MOUNTAIN_CAVE_MIN:1]
[NON_MOUNTAIN_CAVE_MIN:1]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:7]
[TOTAL_CIV_POPULATION:15000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
Pretty sure you'll want to adjust [LEVELS_ABOVE_LAYER_1:50] to a smaller number and random seed of course.
Less concerned with running water and sedimentary stone now, just looking for volcanos+sand+flux in a 2x2, even if the flux is marble since hematite is as common as... dirt around volcanos. I think that seed has one embark with marble+volcano+sand in a 2x2 and another in a 2x3. If you use your own seed be prepared to gen a few times as civs can die pretty easily on these parameters, even though gen ends at year 75.
I got a pretty awesome 3x2 embark on these parameters with a tree covered valley resting behind two mountains with desert steppes leading up like a pyramid out the front and a tiny (2 tiles wide) pass between the mountains linking them up. One of the mountains was a volcano, the magma pipe stopped at ground level but the crater extended WAY up and opened out over the valley in a semi circle. I had to dig a precarious path for the elf and dwarf caravans around and through the volcano since they arrived on top of it and it was so sheer there was no path. Flux and iron etc. The problem? Not a drop of water on the surface and the first cavern was 100 zlevels underground. My guys started dying of thirst because they got bruised ribs from a camel kick and suchlike, which clearly prevented them from getting a beer

I'm just having trouble getting elves to survive in such a small world and get a terrifying forest at the same time, while also getting my flux+volcano 2x2 (in the forest). I'm thinking smaller forests might do it, so the elves can have a regular one and I can have an evil one, rather than having one huge elf forest or one huge evil forest on each map.