Inca Land - Explorations in the Highlands of Peru | Page 6

thermometers, transit, fiber cases, steel boxes, duffle bags, and a folding boat. Our pack train was supposed to have started from Arequipa the day before. We hoped it would reach Vitor about the same time that we did, but that was expecting too much of arrieros on the first day of their journey. So we had an all-day wait near the primitive little railway station.
We amused ourselves wandering off over the neighboring pampa and studying the médanos, crescent-shaped sand dunes which are common in the great coastal desert. One reads so much of the great tropical jungles of South America and of wellnigh impenetrable forests that it is difficult to realize that the West Coast from Ecuador, on the north, to the heart of Chile, on the south, is a great desert, broken at intervals by oases, or valleys whose rivers, coming from melting snows of the Andes, are here and there diverted for purposes of irrigation. Lima, the capital of Peru, is in one of the largest of these oases. Although frequently enveloped in a damp fog, the Peruvian coastal towns are almost never subjected to rain. The causes of this phenomenon are easy to understand. Winds coming from the east, laden with the moisture of the Atlantic Ocean and the steaming Amazon Basin, are rapidly cooled by the eastern slopes of the Andes and forced to deposit this moisture in the monta?a. By the time the winds have crossed the mighty cordillera there is no rain left in them. Conversely, the winds that come from the warm Pacific Ocean strike a cold area over the frigid Humboldt Current, which sweeps up along the west coast of South America. This cold belt wrings the water out of the westerly winds, so that by the time they reach the warm land their relative humidity is low. To be sure, there are months in some years when so much moisture falls on the slopes of the coast range that the hillsides are clothed with flowers, but this verdure lasts but a short time and does not seriously affect the great stretches of desert pampa in the midst of which we now were. Like the other pampas of this region, the flat surface inclines toward the sea. Over it the sand is rolled along by the wind and finally built into crescent-shaped dunes. These médanos interested us greatly.
The prevailing wind on the desert at night is a relatively gentle breeze that comes down from the cool mountain slopes toward the ocean. It tends to blow the lighter particles of sand along in a regular dune, rolling it over and over downhill, leaving the heavier particles behind. This is reversed in the daytime. As the heat increases toward noon, the wind comes rushing up from the ocean to fill the vacuum caused by the rapidly ascending currents of hot air that rise from the overheated pampas. During the early afternoon this wind reaches a high velocity and swirls the sand along in clouds. It is now strong enough to move the heavier particles of sand, uphill. It sweeps the heaviest ones around the base of the dune and deposits them in pointed ridges on either side. The heavier material remains stationary at night while the lighter particles are rolled downhill, but the whole mass travels slowly uphill again during the gales of the following afternoon. The result is the beautiful crescent-shaped médano.

About five o'clock our mules, a fine-looking lot--far superior to any that we had been able to secure near Cuzco--trotted briskly into the dusty little plaza. It took some time to adjust the loads, and it was nearly seven o'clock before we started off in the moonlight for the oasis of Vitor. As we left the plateau and struck the dusty trail winding down into a dark canyon we caught a glimpse of something white shimmering faintly on the horizon far off to the northwest; Coropuna! Shortly before nine o'clock we reached a little corral, where the mules were unloaded. For ourselves we found a shed with a clean, stone-paved floor, where we set up our cots, only to be awakened many times during the night by passing caravans anxious to avoid the terrible heat of the desert by day.
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Mt. Coropuna from the Northwest ------
Where the oases are only a few miles apart one often travels by day, but when crossing the desert is a matter of eight or ten hours' steady jogging with no places to rest, no water, no shade, the pack animals suffer greatly. Consequently, most caravans travel, so far as possible, by night. Our first desert, the pampa of Sihuas, was reported to be narrow, so we preferred to cross it by day and see what was to be seen. We got up about half-past four and