Where a low Andean pass lets Pacific weather systems cross the cordillera, countless storms have deposited immeasurable meters of snow that, over millennia, have compressed into the Moreno Glacier, the groaning, rasping river of ice that’s one of the continent’s greatest sights and sounds.

Fifteen times during the 20th century, the advancing glacier blocked Lago Argentino’s Brazo Rico (Rico Arm) to form a rising body of water that eventually, when the weight became too great for the natural dam, triggered an eruption of ice and water toward the lake’s main glacial trough.

No such event took place from 1988 until March 14, 2004, when the avalanche of ice and water could have been a metaphor for the flood of tourists that invaded El Calafate 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 newly modernized catwalks and overlooks, many visitors spend entire 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; it’s possible, though, to contract full-day “minitrekking” excursions onto the ice (US$129 pp with transport from El Calafate) with Hielo y Aventura (Avenida Libertador 935, El Calafate, tel. 02902/49-1053, www.hieloyaventura.com). Hielo y Aventura also offers a more strenuous “Big Ice” trip (US$150 pp) and a passive “Safari Náutico” boat trip (1 hour, US$10 pp) that approaches the glacier’s face.

Organized tours to the glacier, 80 kilometers southwest of El Calafate via RP 11, leave every day, as does scheduled transportation; transport is usually extra for everything except bus tours.