I thought I was not much of a beach person until a few years ago, when I realized that I actually like beaches which are long and shallow, on seas which are not dead. There are beaches which fit all these descriptions along the Gulf of Kutch near Dwarka. Due to its peculiar shape, the Gulf of Kutch has huge tides twice a day. On one of the days I was nearby, the sea level changed by 8 meters between high and low tides at the end of the Gulf. The coastal shelf is very gentle, so this allows you to walk kilometers into the sea at low tide.
At the Marine National Park near Dwarka, I went for such a walk. This is what I enjoy about beaches, being able to walk for long times at the place where the water and land meet each other. Such places around India are full of hermit crabs which have donned the shells of dead sea animals. Every shells that I saw was on the move. I’d first noticed these zombie shells in the Andamans, where I fell in love with beaches.
I made my way back to the tide line when the horizon started tilting up to the sun. The tide was beginning to turn and I was keen to get away from the slippery rocks and corals while there was still light. The long shadows of the evening threw the tracks of the hermit crabs into clear relief. They seem to be constantly on the move, foraging for food, and occasionally searching for a better shell to move in to. I thought it was a day well spent, doing little other than turning rocks over to inspect whatever is hiding below it.
The high and low tides were at convenient times when we were at Dhanushkodi. The morning’s low tide was at 10:30. This would give us two to three hours at the beach before lunch. We could have a short break after that, before going down to the sea side again for the incoming tide. Sunset was about an hour after high tide. The sun, the moon, and the earth were cooperating with us for a wonderful holiday as we drove down a long narrow spit of land which pointed at the only land border between India and Sri Lanka. That border is a great story, whose beginnings we would see during the day.
Driving to Dhanushkodi at low tide, we saw breakers on the sea to our right. We parked and walked to the beach past a signboard warning us not to go into the sea. I love to tread a path at the very edge of the surf before getting my feet wet; the popping of the millions of tiny bubbles sprays your feet with cool water. This side of Dhanushkodi faces the Gulf of Mannar. The hard packed sand sloped into the waves. The sky was a little overcast, but the contrast of the warmth in the air and the cool water was wonderful. We obeyed the signboards and stayed out of the sea; standing on the beach for breakers to land on our legs.
When we got back in the car, Sathiamoorthy had decided to protect it by laying newspapers on the floor. On the left the level sands stretched far away to the horizon. The waters of the Palk strait was a faint blue line very far away. Clearly this side sloped very little. Sathiamoorthy said something about “soft sand”. Later I realized that this meant quicksand. I would have a much closer look at quicksand later. All I could see from the car was that some parts of the sand looked much more wet than others. I loved the look of the boats beached so far from the sea.
The road now ends at Arichamunai, the very tip of this spit. We walked down to the beach. Along the way we had stopped at empty beaches, but this part was full of people. We walked along the edge of the water, noting the stillness of the water in the Palk strait and the strong contrast with the breakers on the Gulf of Mannar. As we walked, we noticed how the waters are eroding the beach on one side and depositing sand on the other. This turns out to have been studied extensively. The tip of Arichamunai is not a fixed point on the map. It waves back and forth by more than a kilometer when observed for a decade. Sandbars detach themselves, and join the land somewhere else. This is land as fluid as the sea.
When we stepped on to a very wet patch of sand, people around us shouted for us to get back. That’s when I realized that this “soft sand” is quicksand. A policeman had begun to shoo tourists away from this area. It was time for lunch, in any case. We climbed up to the traffic circle. Beyond this beach the extended pattern reefs called Adam’s Bridge or Ramarpalam form a link between India and Sri Lanka. Sandbars accrete around them, some more stable than others. One of the longer lived sandbars, about 15 Kilometers from here nowadays contains the only land border between India and Sri Lanka. If you walked across Ramarpalam from the east, then Arichamunai is where you first know you are in India, from the low-cost version of Ashoka’s pillar planted right at the center of the circle. Some help in recognizing the country is also provided by the rickshaws lined up to take you to Rameswaram, or the many people selling freshly sliced watermelon and pineapple around the circle.
When we came back at high tide the wind had picked up. At Arichamunai the wind was driving the sand very hard. On my legs below my knees I could feel the constant prickling of blown sand. What little I remembered of Bagnold’s classic book verified the evidence of my eyes: the sand grains here are big. The beach is not old enough to have created dust. My slices of pineapple spiced with red chili powder were safe from dust and sand. The sea had come in very close on the Palk strait side. If it hadn’t been for a causeway the Kothandaramar temple (photo above) would have been cut off from Dhanushkodi. I took this photo just before high tide. Right at the horizon you can see a white salt-encrusted sand bar. The day’s tide was too low to drown it.
Walking along a beach before sunrise I saw a piece of brain coral had washed up at night. I have no idea what are the uses of the intricate patterns on the coral. The valleys between the ridges are where the feeding tentacles of the coral rest when they are not waving around. But why is are the ridges so complicated in shape? I had no clue about this. But I thought I should be able to understand the pattern in the sand around the piece of coral.
As the tide recedes, waves break near the shore, and the water runs up the sand. Then, the water drains back. As you can see in the photo above, the water breaks into little eddies as it drains, and the eddies conjure up the pattern in the sand around the piece of coral. You can see a pattern of parallel grooves.
The spacing between them is determined by the viscosity of water. It turn out that if the water tries to drain away with a speed of about a meter per second, then turbulent eddies of size of about 5 millimeters should be seen. That size is about the smallest scale that you can see in the pattern. Interestingly, this gives us a way to see how fast the water drained away after the water has gone. Look at the smallest structure in the pattern left by the water, and the speed should be inversely proportional to this. This means that the finer the pattern, the faster the water drained!
This is all about very small scale patterns. There is much more to the formation of patterns in the sand, as another blog discusses. As I walked about, the horizon began dipping towards the sun, and I was distracted by the easier pattern of the daily sunrise.