Howell posted a score of 94.20 during her first run of the finals, trouncing the rest of the field on a warm and sometimes frightening day down the slushy slopestyle course.
Devin Logan of the U.S. took silver. Canadian Kim Lamarre earned bronze.
Canada has claimed seven medals in four days of snowboarding and freestyle skiing, including three events in which they took two of the three spots on the podium.
Howell's triumph was tempered by a series of scary crashes, including one by teammate Yuki Tsubota that ended with Tsubota being carried off the mountain on a stretcher.
Tsubota was at the end of her second run in the finals when she smacked into the crest of the landing hill. She slid to the bottom and lay motionless for several minutes while being tended to by medical staff. A Canadian official said Tsubota was being checked for a fractured jaw.
It was one of the few setbacks Canada has suffered during a blissful start to the games.
Canada's slopestyle snowboarder Mark McMorris earned bronze in men's slopestyle snowboarding on Saturday and Canada went one-two in both men's and women's moguls.
Only Logan's acrobatic run to an 85.40 in the slopestyle skiing finals broke the run of dominance. Her medal-winning sprint included a frontside 720-degree spin in which the 20-year-old - who is coming off a second torn ACL in her knee - gamely held on while landing.
Still, it was no match for Howell. The 19-year-old former figure skater pulled off the run of the meet, ending with a 540-degree spin while grabbing the front of her skis. She shook her head in disbelief as she cruised into the scoring area and her mouth dropped when her score was revealed.
Whoa Canada indeed.
She had gold all sewn up when none of the other 11 skiers could top her during their second run and enjoyed a delightful victory lap before joining her teammate on the podium. Howell and Lamarre embraced, a touching end to a difficult day for a sport making its Olympic debut.
Canadian Kaya Turski, six months removed from a third ACL surgery and battling a virus, failed to make it out of qualifying. Considered a pre-race favorite, Turski wiped out during both of her runs, lying on the snow for several moments when her Olympics officially ended.
She was hardly alone in a field that struggled to put on much of a show in soft conditions on snow better suited for a snowcone than an Olympic debut for a discipline trying to prove it's just as cool as its snowboarding cousins. Nearly half of the 44 qualifying runs over the series of rails, jumps - and one oversized Russian nesting doll - ended with a skier face down in the snow or pulling out of self-preservation.
