The Giant Blocks of Bath Pumice

Written 5 August 2011

During a long stretch of the flight into our first campsite, the helicopter flew parallel to and just west of the Kampankis range. Out the windows to the left was the broad floodplain of the Rio Santiago, and out the windows to the right was a cliff face of chalk-colored rock all overgrown with green. The edge of that same cliff is now only a couple of kilometers from camp, and on our first day in the field I asked David if the strong desire I felt to see what was growing on it was scientifically defensible or just boyish enthusiasm. In his mild way he replied: “I often find interesting things growing on the edges of cliffs.”

So on the first morning the entire botany team – Isau, Camilo, David and I – took up our collecting sacks and headed up the trail that led in that direction. Guillermo, who’d overseen the trail cutting, had warned us in Tarapoto that the trail didn’t make it all the way to the edge of the cliff but stopped a couple of hundred meters short. 

“Why’s that?” 

“Because giant blocks of bath pumice got in the way.” 

“Giant blocks of bath pumice?” 

“You know – the kind you scrape your feet with. We tried to get around them but we couldn’t. We had to give up….” 

Now there are plenty of things at the base of the Andes that can prevent a person on foot from getting from A to B: rivers, swamps, crevasses, stands of spiny bamboo…. But giant blocks of bath pumice? 

“Giant blocks of bath pumice?” 

“That’s what they look like,” said Guillermo. “But you can hardly walk on them. They’re sharp – they’ll cut up your boots – it’s ugly.” 

“And are there plants growing on them?” 

“Plants? You bet….”

So we went. From camp the trail climbed a ridge, descended to a stream, climbed another ridge, ran along the edge of a steep hillside where Camilo muttered “tapir track,” descended to another stream, climbed another ridge…. We went along filling our collecting sacks; the morning got warmer and the sacks got heavier. After a couple of kilometers the trail left off twisting and turning and headed uphill in a more businesslike way. We trudged up past a place where the trail passed over rocks riddled with fossils, then past a place where the forest looked perfectly normal except for the fact that all the thickest tree roots ran along the surface of the ground instead of underneath it, and finally we reached a spot where the trail made a sudden turn to the left because the way forward was obstructed by giant blocks of bath pumice.

The giant blocks of bath pumice.
Photo: D. Neill

Geologically-minded readers are going to have to gnash their teeth a while longer, until I can report what Vladimir, the geologist on the team, has to say about those craggy gray rocks. Our first impression was the same as Guillermo’s: it looked as if a piece of the moon had dropped into the Amazon, where it had shattered into a thousand blocks and been covered up again by forest. The rocks continued on the same uphill slant for as far as we could see, and something about the light far in the distance made it seem as though the escarpment was within reach. And so the boyish enthusiasm started saying: “Let’s go up and have a quick look. How hard can it be? It’ll just take a minute.”

The challenge facing the botany team.
Photo: D. Neill

The first three meters took a minute. On their upper surface the rocks are riddled with little pits about the diameter of a coin, and between the pits the rock that hasn’t been eaten away sticks up in jagged shards. You walk on top of these shards, which means that before every step you want to test your footing two or three times before shifting your weight, and you go forward expecting at every moment one of those sharp stone splinters to come through the sole of your boot and spoil your day. Every couple of steps you have to straddle one of the crevasses that gape between the blocks, and pretty soon, climbing upwards practically on all fours, you discover that the rocks can cut your hands too. In places the rocks are covered with roots, or herbs, or little mats of leaf litter, but mostly it’s the exposed gray rock, slanting upwards towards what now, upon reflection, seems like a very far-off cliff. Also – centipedes. During the first fifteen minutes on those rocks I found three species, one of them bright yellow and so thick that at first I thought it was a snake.

It reminded me of walking on a reef at low tide, on one of those afternoons when you’re wearing flipflops and the going underfoot is sharp but seeing what’s in those tidal pools up ahead is going to be worth a few cuts. So I made my way along those rocks thinking “I should probably head back now” and “I’ll go back in a second” and “I’m going back now” and “I’ll just have a look up here before going back” and “Hey, there’s a terrestrial orchid up here” and also “Centipedes!?” Now and then, spotting an interesting plant, I remembered what I was doing there. Then I’d double-check my footing so that I could reach out for the plant and make the collection, until I remembered that my collecting sack was back at the trail – ten meters away – an impossible distance. The next minute I’d feel one of those spiky rocks shifting under my feet and starting to tilt, I’d have to scramble onto another in a panic, and the specimen would disappear down one of the crevasses.

The rocks proved too much for the botanists on this day.
Photo: D. Neill

Reader, we retreated. Our sacks were already full from the hike and we had plenty of other material to press, so we climbed down from the rocks and headed back down to camp in the hot afternoon. That was yesterday. Today Vladimir has gone up that same trail with his rock hammer and his muriatic acid, and Alvaro and the guides are going to try to punch through a trail to the cliff, so stay tuned – we’re not done with those rocks just yet.

Post by Nigel Pitman, Conservation Botanist