It was roughly 4am and I was going through that deep, dream-intensive slumber that seems only to come in the last hour of sleep. The day before I had been on a beautiful, adventurous day into the Krabi’s Ao Luk province, and I had seen sand boiling in that rough terrain. I woke suddenly, with that image of sand in my mind. I had to find out what that thing was, so I turned on my Mac and started searching for sand boils…
They are indeed called Sand Boils (or Sinking Sand, or Liquefaction). Unfortunately there is mixed, incomplete and wrong information about this phenomenon in the Net. Some sites compare it to quick sand, which is not. Google informs me that sand boils are almost entirely bad: several pages lead me to broken levees, levee failure during flooding, the aftermath of earthquakes, houses subsided into liquefied ground and more to prove these sand boils are portents of doom, signs of catastrophic failure.
You have to click your way past dozens of these disasters before you hit the truth. Sand Boils are underwater fountains kicked up by spring water rising through a sand mass, sometimes a result of a continuing quiet process lasting a few thousand years. Normally, layers of sand and silt underground bear the weight of whatever is on top of them through a network of contacts between individual soil grains. Practically, sand boils occur when water under pressure wells up through a bed of wet sand. During an earthquake, this network is disrupted, but what is on top is still there, being all heavy and giving away pressure. When the sand is wet, anything that jiggles it, agitates it, shakes it, joggles it, jolts it, quakes it, quivers it, shudders it or vibrates it, make the overburden pressure to be transferred to the water which, squeezed up, can find a suitable weak spot and will squirt out into a sand boil. This is the reason why we triggered the sand boils by the simple clapping of hands: we sent sound waves out.
You can have a practical experiment to prove this. Put some sand in a bucket, place a small block on the top of the sand, and gradually saturate the sand with water. The block still rests on the surface. Now, strike the bucket sharply, and watch the block quickly drop. It is basically like shaking a can of a fizzy drink. Pressure builds up, and when you release it, the fluid comes shooting to the surface.
So why did that sand not support any weight yesterday when we tried to sink in a wooden stick? While sand can act like a fluid, it is a non-Newtonian fluid which means it will not act like water. You can stand on it when it is stationary, for example, but not when it is fluidized. Sand boils where a surprise for me and my tour companions, a surprise coming from a region of Thailand that I have called home for so many years: Krabi!
A tour into Ao Luk province in the north of Krabi region uncovers a wonderful escape to the tourism trap, as well as allowing you to see sand-boils. Swimming, kayaking, trekking, cycling, it’s all there for you to enjoy it, and in a ‘green way’. Check out http://asianitinerary.com/northern-treasures-at-ao-luk/