Ah, look! Someone (Marcus) caught me obsessively photographing the rocks:
I have to admit, I went to the Sentosa monitoring trip with a sly ulterior motive - I was dying to take a look at the Sedimentary Rock Cliffs and caves by the coast. I have to say, I was totally blown away.
Alright, before I go any further. Let me first explain what are Sedimentary Rocks. I know most people are probably thinking ROCKS ARE ROCKS, THEY ARE STONES. THE END. but NO! As I have previously harped about, rocks are really records of the Earth's geological history. These historical records can be divided into 3 main groups:
1) Igneous Rocks - Rocks form when volcanic lava cools E.g Granite
2) Sedimentary Rocks - Rocks which are depositions of other eroded materials, and overtime get cemented together E.g Limestone
3) Metamorphic Rocks - Rocks which are formed under intense heat and pressure E.g Marble
So, the cliffs at Sentosa are Sedimentary in nature, namely, they are made of Sandstone:
notice the 'layers' that seem to mark the cliff, this is a characteristic of sedimentary landforms (pls click to enlarge, small pictures dont do these magnificent landforms justice!!!!!!!!!!!)
Also, notice that the cliffs are often bare and un-vegetated. This shows that the erosion processes, driven by the wave actions, are very active. Hence, this part of the island is actually receeding inwards, even now as I type!
A view from the shore:
some of us have the impression that cliffs are like:
These cliffs are what I call "geologically mature" cliffs. They go through millions of years of weathering and erosion. and just look at the size of the waves in this above picture, its difficult for Singapore waves to possess THAT much energy as we are surrounded by the Indonesian archipelago. Thus, our cliffs are relatively small, but no less special, as compared to the above.
Who knows, maybe with the tectonic shifts in the region, the cliffs at Sentosa could be like that in 20 million years! (:
anyways, back to my point - here are some observations i made about the cliffs:
(disclaimer: due to the appalling lack of academic literature about Sentosa's Cliffs, these observations are NOT cross referenced)
#1 Can you see that the rocks are kinda tilting in one direction? To help you see, i've drawn some very straight (ahem) arrows on the close up below! This means that the rocks are arranged in such a way that they are Landwards dipping.
This makes this side of the cliff fairly stable - meaning there will hardly be events like Rockfalls or Avalanches. This postulate is supported by the fact that there are no rock debris at the bottom of the cliff.
#2 THERE ARE NATURAL-CAVES IN SINGAPORE:
These caves form at the base of the cliffs, and these are the weakest areas of the sandstone. What do i mean by weakest?? meaning they are the most severely jointed area i.e. they have the most lines of weakness for water to penetrate and weaken the internal structure! such as:
see all the lines and cracks? There's actually a small cave in the making in the pic, try to spot it!
I wanted to duck into the caves for a look, but i was told gigantic spiders lodge in there... *BACKS OUT INSTANTLY* HAHAHAHA. maybe next time (or not).
Lastly, landslides are not uncommon at this side of Sentosa! I love this retaining wall, for some weird reason, it blended right in with the coastal landscape. i almost missed it! Behind it is a bunch of weathered material, clay probably, from the looks of it.
Well, there you have it. Despite the multiple and rather obsessive coastal reclamation (Labrador beach is the ONLY natural stretch in our Southern Coast), these beautiful cliffs remained untouched and often unnoticed. The date of this ONLY bit of graffiti state FEB 1979.
I would hate to think about the day when the government decides that one IR on sentosa is not enough, and this undeveloped bit gets reclaimed as well. Or worst still, this part gets commercialize and becomes part of the STB marketing scheme. so, before all that happens, i hope that my little blog post about this relatively unknown side of Sentosa has opened some of your eyes (:
this is our geological history!