Galapagos Cruise Report: Isabela Island

From the National Geographic Islander in Galápagos August 19, 2010

Urbina Bay • 8:45 AM

The day dawned with light clouds and deep rolling swells; we were anchored off of Urbina Bay, on the west coast of fabulous Isla Isabela, roughly in the center of the seahorse-shaped island. Long, low, massive shield volcanoes loomed in three directions: the volcano that is Isla Fernandina just to our west, Darwin Volcano on Isabela to our northwest, and, by far the closest of the three, Isabela’s Alcedo Volcano just to the east of the bay. I was especially excited to visit Urbina Bay, being the site of just the kind of spectacular geological uplift that so fascinated Charles Darwin in his geological studies of South America. On his voyage around the world on H.M.S. Beagle (1831-1836), Darwin resolved to make observations that would help test the geological theories of Charles Lyell, as put forth in his book Principles of Geology. That book, the first volume of which was published shortly before Darwin departed on the Beagle voyage, articulated an exciting new way of looking at the earth: constantly acting natural processes like erosion and volcanism slowly shaped the face of the globe.

Some found our wet landing at Urbina Bay a bit wetter than usual, owing to heavy surf, but a solitary flightless cormorant (Phalacrocorax harrisi) fishing near the shore didn’t mind the rough waves one bit. Once high and dry on the beach, we headed inland with our indefatigable naturalist, Fausto Rodriguez, on a trail that took us through classic arid-zone vegetation dominated by thorn scrub (Scutia spicata), Yellow cordia (Cordia lutea), Waltheria (Waltheria ovata), and, most beautiful of all, Darwin’s cotton (Gossypium darwinii). The 5 cm cotton flowers, lustrous yellow with a rich maroon deep inside at the petal bases, contrasted spectacularly with the surrounding scrubby vegetation. Quite a few bolls were evident too — three-lobed structures with tufts of white cotton fluff. Some of the cotton flowers had a soft pink tinge, indicating they were older flowers. Native carpenter bees (Xylocopa) abounded — large fuzzy black bees were constantly moving among the cotton and Waltheria flowers.

While I was getting a close look at a cluster of glowing white Cordia fruits, I suddenly became aware of a huge land iguana (Conolophus subcristatus) just under the shrub. It was an enormous (~1 m) and seemingly fat individual, maybe recently fed, with a gorgeous rust-red mottled coloration that blended in with the dry grasses and other withered dry-season herbs. This beautiful iguana proved to be the first of several that we would see on this hike, and it wasn’t long before we began to notice just how abundant their burrows are here. Walking up the trail alert for more iguanas, we suddenly glimpsed a very large lumbering form way up ahead in the middle of the trail. It was a giant tortoise! The tortoise was fairly young, perhaps 1 m head to tail (or snout to vent), down from the highlands for the dry season. Given the locale, this was likely Geochelone elephantopus subsp. vandenburghi. Our Naturalist quickly had us crouch down so as to minimize alarming the tortoise by our size. It slowly and steadily ambled down the trail, to our amazement and delight, pausing about 5 m from us. I think it was trying to figure out what we were — it extended its head out and up, slowly swinging it to the side and holding it there with a single wary eye in our direction. The tortoise held that position for what seemed like 10 minutes or more; they have all the time in the world, and standing there to regard us for a full day probably would have been nothing at all for such a long-lived animal! We remained crouching and moved to either side of the trail to clear the way in case it wanted to continue its trek down the trail, but I suppose it decided we were too suspect, and it turned off the trail. When we walked over to get a closer look we noticed an even larger tortoise on the other side of the trail! That was a treat too, but I will never forget the sight of that first tortoise lumbering along the trail as its ancestors have for millions of years. This trail was human-made, but I thought about how the whalers and buccaneers and others who hunted the tortoises would often find them, and fresh water sources, by locating well-worn trails made over the millennia by the tortoises.

As we continued along we saw quite a few Darwin’s finches (mostly small and medium ground finches, Geospiza fuliginosa and G. fortis) and the ever-curious Galápagos mockingbirds (Nesomimus parvulus); they often landed in the trail and ran towards me, seemingly to get a look, before flitting up into a bush. I was excited to find some new botanical delights along the trail, including an endemic shrub named for Darwin by his friend Joseph Dalton Hooker: Thin-leaved Darwin’s shrub, Darwiniothamnus tenuifolia! Like many shrubby endemics of the Galápagos, this plant is in the sunflower family, a fact readily revealed by its beautiful smalll daisy-like flower. This distinctive plant has dense brushy growths of narrow leaves, each about 4 cm long, culminating at the branch tips with small clusters of lovely white flowers. I also found an elegant plant with an inelegant name: Wartclub, Commicarpus tuberosus, with delicate little trumpet-like purple flowers on largely leafless stems. One less savory sight was an introduced brown rat, which for some reason was either unalert or ailing, as our Naturalist was able to dispatch it with a few well-placed whacks with a stick. We felt a pang of sympathy for the dying rat, but only a pang — the destruction they wreak on native fauna is staggering.

All along the trail there was evidence of the uplift that pushed this portion of the island, once seafloor, high and dry. Many of the volcanic rocks were encrusted with barnacles and tubeworm shelters. Once the trail looped back toward the beach, we came upon huge bleached coral heads – the clearest evidence of the uplift yet. Given the rapidity of the event, we tried to imagine the landscape with dead and dying sea life gasping for air — it would have been a bonanza for seabirds, at least for a short time. Imagine the stench of all that rotting sea life! I thought again how Darwin would have been excited to see this phenomenon. In Lyell’s view, at all times some parts of the earth were experiencing slow uplift, balanced by subsidence in other parts. Darwin was eager to find evidence in support of Lyell’s idea, and was very excited to find clear evidence of uplift along the west coast of South America (including an uplift episode following an earthquake he himself experienced). Darwin was 119 years too early for this example though — the uplift of Urbina Bay occurred just in 1954.

It was now getting a bit late; the tide was coming in and we hurried along the coast to our landing site before the tide rose high enough to block our path. But not before admiring a few more botanical beauties – notably White Leadwort (Plumbago scandens) in bloom, with phlox-like white flowers and sticky glandular hairs on the stem. Timing was everything for our disembarkation, both in terms of making it along the narrowing strand to the landing site, and in terms of the narrow window of opportunity for dashing to the Zodiac when the surf momentarily went out. We got back to the ship by 12:30 PM, admiring a whimbrel (Numenius phaeopus) just before leaving the beach.

Punta Morena

During lunch the ship moved south along the west coast of Isabela, to Punta Morena, where we made an afternoon landing to explore the vast basalt fields between volcanoes.

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