Issue link: https://bluemagazine.uberflip.com/i/25040
An increase as small as � �@1l'@@ffi� iIDlႀ䊉@lW@ ffi@1l'lliill�n can quickly suffocate or leave you unconscious. At altitude, oxygen deprivation settles into the body slowly, over several thousand feet. Underground, carbon dioxide levels can vary substantially from one step to the next, or just around the corner. Carbon dioxide settles to the lowest point, which is bad news for vertical cavers who are looking for the bottom. Another problem with vertical caves is that pressure changes outside can effectively suck breathable air out of the cave. You could end up racing the air for the exit. We began retracing our steps to "good air." The tight passages and ascent up our previous rappel lines took time and complicated our retreat. The climb up those ropes in the face of a ful l-on waterfall was like fighting a boxing match. By the time we reached the top we were wet, out of breath and physically beaten. As we neared the main entrance and glimpsed the light outside, a movement caught my eye. I looked up to see thousands of bats peering down. They were waiting for dusk-the beginning of their mass exodus and renewed search for food. My eyes adjusted as a snake dashed back into its hole with a bat clamped firmly in its jaw. I reminded myself that these cave racers are highly poisonous but supposedly prefer other animals to humans. We made our way toward the warm sunset and into the surrounding jungle. Northern Thailand's mountains are integral accomplices to finding potential caves. We were in postcard-perfect karst topology. The sheer walls and lengthy ridgelines redirect rivers and runoff. Our strategy had been to follow a river until it ended abruptly at the base of a mountain. Below the mountain surfaces, water erodes the limestone and non-carbonate stone, leaving polished and tubular passageways. This combination of a steady water supply and limestone creates an ideal breeding ground for long, deep caves which often house brilliantly decorated rooms-all built one drop at a time over thousands of years. Polished limestone tubes alternate with rooms 40-feet high, as ornate as any palace. These rooms are often bright white, jeweled with quartzite. They commanded respect. I half expected to find the Holy Grail. In our cave quest we trekked through jungles and across smoldering fields; the blackened ash and thick smell of smoke were a constant reminder of the region's slash and-burn agricultural practices. It was the peak of the hot season. There was nothing left to harvest, so villagers laid low, anticipating the oncoming rains that would ignite the new growing season. The only activity was the festival of Songkhran, a celebration of the lunar New Year. Thai chi ldren had adapted the ritual of cleansing Buddha 54