Where a low Andean pass lets Pacific fronts cross the cordillera, countless storms have deposited hundreds of meters of snow that, over millennia, have compressed into the Moreno Glacier, one of the continent’s greatest sights and sounds. Fifteen times during the 20th century, this groaning, rasping river of ice blocked the Brazo Rico (Rico Arm) of Lago Argentino to form a rising reservoir; eventually, when the water’s weight became too much for the natural dam, it triggered an eruption of ice and water toward the lake’s glacial trough.

No such event took place from 1988 until March 14, 2004, when the avalanche of ice and water might have been a metaphor for the flood of tourists that waited in anticipation. On any given day, though, massive icebergs still calve off the glacier’s 60-meter face and crash into the Canal de los Témpanos (Iceberg Channel) with astonishing frequency. Perched on catwalks and overlooks, many visitors spend whole days either gazing at or, eyes closed, simply listening to this rumbling river of ice. Descending to lake level is prohibited because of the danger of backwash and flying ice chunks.

Organized tours to the glacier, 80 kilometers southwest of El Calafate via Ruta Provincial 11, leave every day, as does scheduled transportation. It’s also possible, though, to contract a full-day “minitrekking” excursion onto the ice (US$83 pp) with Hielo y Aventura (Av. Libertador 935, El Calafate, tel. 02902/491053, www.hieloyaventura.com). Hielo y Aventura also offers a more strenuous “Big Ice” trip (US$115 pp) and a more passive “Safari Náutico” boat trip (US$9 pp, one hour) that approaches the glacier’s face.