Brian Weitz, more widely known as “the Geologist” of Animal Collective, spent 2004 researching oceans, fisheries and the Coast Guard for a Senate Commerce subcommittee.

On Tuesday night, he and his three bandmates helped work a sold-out 9:30 Club crowd into a drenched, sweat-soaked mess while psychedelic fish cartoons and trippy bubble patterns floated across the inflatable tentacles and teeth surrounding the stage.

The Baltimore-formed band mesmerized the crowd with hits from its ninth studio album, “Centipede Hz,” and provoked jumping, moshing and glowstick-waving with tracks from 2009’s critically acclaimed “Merriweather Post Pavilion” (named for the Columbia, Md., venue).
https://www.youtube.com/watch?v=nagI_slIviA

Weitz, who told The Washington Post in September that he once had his sights set on “lobbying for conservation organizations,” left Capitol Hill in 2005 and, to the benefit of experimental music fans everywhere, devoted himself to musicianship. He currently resides in the H Street ‘hood.

To the disappointment of District fans, Animal Collective has not graced the 9:30 Club since May 2009. Though they have appeared at Merriweather Post Pavilion’s amphitheater. Tuesday was night two of three sold-out shows, but the band’s Monday performance was canceled by a power outage.

Electronically recovered, the club lit up in blinding purple strobes during the new-agey beats of “What Would I Want? Sky” and blazing orange and crimson flooded the backdrop in coordination with the trippy melodies of “Applesauce.” During “Peacebone” and the fan favorite “The Purple Bottle,” — the two encore songs — the set mimicked a Technicolor kaleidoscope.

The quartet chose to let silence and darkness descend on the stage during breaks in its 90-minute set. The caving headlamp Weitz sports to see his electronic equipment during live shows often served as the sole source of stage light between songs.

The crowd, a plurality of whom were sporting the club’s cupcake-shaped underage stamp on their hands, bounced, shrieked and managed to support a handful of crowd surfers. Sweat droplets seemed to rain from the ceiling.

Animal Collective returns to the 9:30 Club on Wednesday night.