As part of our homeschool lessons over the past few weeks, Ethan and I have been studying and discussing Tropical Coasts and Ecosystems. Our recent trip to Koh Samui in Southern Thailand made for a perfect, and relevant field trip.
Our vacation rental was located across from Bang Makhon Beach near the northwest corner of the island and it was an optimal spot for beachcombing. We set off on a long walk at the peak of low tide so that we could wade as far out toward the reef as possible and observe as much as we were able.
Heading north along the beach toward the headland, I pose some initial questions for Ethan to ponder. “Why do you think there is a wide, sandy beach here but a mountain up there where we’re going? What do you think we will find when we get there? And why do you think the beach here is so wide and flat?”
As we wandered and played and explored, we observed that the sand in the tidal flat area is incredibly fine, sometimes muddy,and almost powdery. There are numerous shallow tide pools, some only inches deep. To the east, toward land, the beach steepens slightly and we note that the sand becomes a lot coarser than out in the tide flat area…hmmm, what might be a reason for that?
A variety of ripples found along the beach:
As we wade through the pools, we can feel that the water in some of the pools is actually very warm – almost uncomfortably warm. We don’t observe any creatures swimming around in these waters, or any plants, or even algae, growing here either. We do observe small mounds of sand from time to time where we suspect a burrowing creature hides. A crab? Some kind of clam?
We talk about how we learned that the very warm water in the tidal areas tends to be very low in oxygen (vocabulary word: anoxic). One of the things we talk about as we cross the seemingly barren tidal flats, with the warm pools of water is how we learned that the sands in these tidal areas are teeming with various types of micro-organisms, such as cyanobacteria, that live on and in the sand. We wonder what they eat? And being an ecosystem field trip, what might eat them?
As we continue north toward the headland, the beach gets narrower, we get closer to the reef and the water gets deeper. The water here is not in isolated tidal pools, but is fresh ocean water and noticeably cooler. We begin to observe the occasional appearance of bumpy rock mounds – dead corals, maybe? We also see little critters scatter before us as we wade through the water. Closer inspection reveals small, white crabs darting about. Could this be what was burrowing into the sand that we saw earlier? What might they be feeding on?
We also start to see that the deeper, cooler water hosts small seagrass beds. We’ve been discussing these and how seagrasses live below water (below the mean tide elevation). If we encounter them, we know that the tide does not usually get lower than the level of these seagrasses. I ask Ethan to wander around one of the beds and see what he can see. Does he observe any creatures in the seagrass? Can he make any observations about the seagrass? Is it all the same or is some of it different? How does is grow and spread? Can he see any flowers or roots or anything at all? Actually, we don’t know what species of grass it is, but it turns out to be pretty much all the same (vocabulary word: homogenous).
Walking up to the boulders on this rocky headland, Ethan declares this our personal Pirate’s Cove. As we climbed to the top of our Pirate Fortress, we couldn’t help but feel pretty satisfied with ourselves as we gazed out at the emerald waters of the open ocean and the sounds of the waves crashing below us. Wait! Did you say waves crashing? That’s right, once out where the reef meets the shore, there are waves crashing…hmmmm, now isn’t that interesting?
As we explore, I point out a few different examples of the fascinating geology that we encounter, such as the dark rock that appears to be twisting and squishing it’s way through the lighter colored rock; the way the rocks are layered and tilted at an angle; the rocks are crisscrossed by straight cracks that are at a right angle to each other; how some of the rocks below the high tide line are polished and curving; how the lighter colored rock gets more and more colorful with shades of red as we approach a very thick layer of the dark rock.
Our walk on the beach made for a great adventure and a great opportunity for me to pass on some of my passion for geology and earth science. Plus, we got to be pirates. Argh!