Andean Northwest
Andean Northwest Geography & Climate
Geography
The Andean Northwest climbs from subtropical lowland to the high puna within about a hundred kilometres, and that gradient produces an extraordinary range of landscapes.
The puna
The Argentine portion of the altiplano sits above 3,500 metres — a cold, dry, treeless plateau of salt flats, volcanoes and lagoons stretching toward Bolivia and Chile. Salinas Grandes is the accessible salt flat; further west the country becomes genuinely remote. The volcanoes along the Chilean border include Llullaillaco at 6,739 metres, which holds the world’s highest archaeological site.
The quebradas
Rivers cutting east off the plateau have carved deep canyons through sedimentary rock laid down over hundreds of millions of years and then folded and lifted. The Quebrada de Humahuaca exposes those layers in bands of red, ochre, green and violet — the colours are mineral, from iron, copper and manganese in successive strata.
The yungas
On the eastern slope, moist air off the Atlantic rises and condenses, producing a narrow belt of subtropical cloud forest that is among the most biodiverse habitats in Argentina and sits, remarkably, within sight of desert.
The Calchaqui valleys
Running south from Salta at 1,600 to 2,500 metres: red rock, cactus, vineyards and eroded formations.
The Tren a las Nubes route
The railway from Salta to the Chilean border climbs from 1,200 metres to over 4,200 in about two hundred kilometres, using switchbacks and two complete spirals to gain height, and crosses the Polvorilla viaduct on a curve at 4,220 metres. It was built in the 1920s and 1930s as a freight line to the borax and mineral workings of the puna, and the engineering is the reason to take it rather than the destination.
Seismic and volcanic
Active throughout, with a history of destructive earthquakes.
Climate Patterns
The northwest’s climate is governed by altitude and by a short, intense wet season, and the daily range is larger than the seasonal one.
The dry season
April to November is almost rainless, with brilliant clear skies. In the Quebrada at 2,500 metres, days reach 20 to 25°C and nights fall to near or below freezing — a swing of twenty degrees or more is entirely normal. On the puna above 3,500 metres the days are cold and the nights severe, regularly below −10°C in winter.
The wet season
December to March brings the invierno boliviano, heavy afternoon storms driven by moisture from the Amazon. Rivers that are dry gravel for eight months fill in minutes, and landslides and washouts close the Quebrada road and the mountain passes. The salt flats can flood, which makes them a mirror and also impassable.
The eastern slope
The yungas cloud forest catches that moisture and is humid and green year round, a startling contrast to the desert on the other side of the ridge.
Sun
Ultraviolet at these altitudes is extreme. Burn happens fast even on a cold day, and reflection off salt makes it worse.
Two climates within an hour
The gradient here is abrupt enough to be disorienting. Leaving Jujuy at 1,200 metres in shirtsleeves, you can be at 4,170 metres on the Lipan pass within ninety minutes, in wind and near-freezing air, and back down to the yungas cloud forest the same afternoon. Layers are not optional, and a warm jacket belongs in the car even in January.
Altitude
Passes over 4,000 metres are routine on the puna routes, and the effects are real — see health.