Our itinerary for today would begin with a trek along the Ma Shi Chau Nature Trail, a trail lining the coastline of Ma Shi Chau, an island linked to the Sai Kung peninsula of Hong Kong by a coastal feature called a tombolo, followed by a visit to the picturesque High Island Reservoir - a Geopark renowned for its magnificent hexagonal columns of rhyolitic rock formed from past volcanic eruptions in Hong Kong.
As our morning began with a rocky terrain trail at the interestingly named 'Ma Shi Chau' (direct translation: horse excrement island- I will elaborate more on this later), we were greeted with a blast from the past when we saw the quaint little fishing village that welcomed us at the start of our trek. Guided by our knowledgeable and witty Geopark guide, affectionately known as Uncle Sam, our lungs were injected with fresh air (not something you'll breathe in everyday Singapore) as we embarked on our hike up a hill that we had to cross before arriving at Ma Shi Chau.
Lining the hillside were graves of a traditional cemetery, and Uncle Sam generously took the opportunity to enlighten us on the traditions and customs of the people there as well as how the islands were named. Basically, in the case of Ma Shi Chau, it all began with a mountain that the first settlers thought looked like a horse saddle and thus, based on its naming as "Horse Saddle mountain", a trend of naming the landmarks based on horses was created; Ma Shi Chau interestingly was thought to look like horse excrement in the channel. We also learnt that a custom known as "twice burial" was often practiced where the body of a deceased will be dug up after an initial burial after some time before being cremated.
After passing by tens of graves and scaling hundreds of steps- we finally reached our first location of a tombolo. It was really refreshing and enlightening to finally see our textbooks come to live! As the Hong Kong government wanted to preserve the tombolo in the event of a typhoon, the reinforcements and coastal management we have tediously memorized came alive to us - we saw how they used salt water resistant vegetation and rocks to reinforce the tombolo, where the roots of the vegetation would stabilize the tombolo and the rocks will allow deposition to continue occurring. The idea of using salt resistant plants also made sense in the saltwater/coastal environment, and through this, we leant about the importance of contextualisation and understanding the knowledge rather than just memorizing off the textbook.
Using the tombolo as our bridge, we arrived on Ma Shi Chau. It felt incredibly surreal to be standing on rocks millions and millions of years old, making it almost impossible to imagine the scale of things and these majestic processes of earth movement.
According to Uncle Sam, Ma Shi Chau is largely of sedimentary origin, comprising mainly of siltstone, mudstone and sandstone with some intrusions of solidified magma as well as sedimentary rocks that had undergone heat and pressure, resulting in the presence of metamorphic rock such as quartzite.
What struck us the most was the extremely clear joints and bedding planes inscribed on the rocks due to lithification as well as tensional forces from plate movement. At one point, we were even able to see an intrusion of solidified magma between two bands of sedimentary rock and it was incredibly interesting to see these two different types rocks juxtaposed next to each other, one about a 100 million years older than the other, according to Uncle Sam.
As we trekked along the nature trail, we were able to feel and even scratch at the different rocks before our eyes. For example, mudstone, being comprised of mainly mud, allowed us to leave marks on these rocks using our fingernails. It really changed our perspectives of rocks- we'll no longer be able to view them as just meaningless objects we come across with everyday but as the diverse by products of the earth, each having its own story to tell.
During this trek,we were also able to differentiate the different types of rocks confidently after seeing them in the flesh. We were able to tell apart the minerals that make up Granite; we could easily identify quartz veins found within granite and quartzite; we also learnt that weathering processes all take place together, but depending on the environment and mineral composition, one process might be more dominant than others. What made our little adventure all the more exciting was knowing that these rocks were in their original form- never tainted by man but only the forces of nature such as coastal erosion and weathering processes acting upon them . It was almost like a buffet of lithosphere spread before our very eyes! The various forms of weathering finally had so much meaning, it was like living in our lecture notes seeing all the processes in the flesh; and at that point, we finally could understand how amazing physical geography was as we got to experience it and see it first hand for ourselves.
Following that, we visited the High Island Reservoir/Dam area, one of Hong Kong's most popular geological sites, located in New Territories. Built in the late 1970s, the High Island Reservoir, the largest reservoir in Hong Kong, was created by damming the two ends of a narrow sea channel, of which the Eastern side overlooked the Pacific ocean. For the construction of the dam, not only did we learn that villagers were being shifted to the Downtowns of Hong Kong, submerging half of the villages there, it also revealed the magnificent volcanic rock site of rhyolitic hexagonal columns of rock.
When we arrived at the destination, we were intrigued by this huge structure known as a “Dolosse”. These dolosses were placed near the edge of the protective dam (yes, a dam was constructed in front of the main Eastern Dam for protection purposes) as a mean to protect the protective dam and main Eastern Dam (this dam overlooks the Pacific Ocean) from the impacts from disastrous typhoons during the typhoon season. Just this alone allowed us to appreciate how hydrology, coastal processes and atmospheric processes were interlinked with one another.
At the beginning of the trail, we saw two different types of rocks – granite, which is a type of intrusive igneous rock as well as rhyolite, an extrusive igneous rock. The granitic rocks displayed were transported and placed there manually. Granite is a hard, coarse grained rock, primarily consisting of feldspar (which is pinkish/brownish in colour), mica (which is black) and quartz (which is white and glassy). It obtains its coarse-grained texture due to the slow process of solidification and crystallisation of magma beneath the earth's surface (hence its classification intrusive igneous rock).
On the other hand, rhyolite, its counterpart (they comprise of similar minerals) is fine-grained due to rapid cooling of rhyolitic magma on the surface of the earth (hence its classification as extrusive igneous rock). Being able to touch and see granite and rhyolite allowed us to better comprehend the properties of these rocks.
Proceeding on, we spotted a domical, isolated island detached from the High Island, due to coastal erosional processes. Part of the hill (known as Flower Mountain) underwent erosion and a sea cave developed over time. When the cave wore through the headland, an arch developed. Overtime, a stack formed when the connecting part of the arch was eroded by hydraulic action and weathering which then gave rise to the stack we saw before our eyes. A stack is basically an isolated island/pillar/rock formation. This stack is also known as Po Pin Chau. The highlight of High Island Geopark was the hexagonal columnar joints, standing as high as 30 metres.
The High Island Formation is said to have formed inside a huge caldera following a catastrophic volcanic eruption some 140 million years ago. When the lava flowed rapidly into this depression, it created a semi-enclosed environment which was beneficial to slow cooling. When the lava cooled down slowly, it gradually developed contraction joints. The joints extended perpendicularly downwards during cooling of the rock. The contraction of the cooling rock goes towards the centre to form high hexagonal columns.
All in all, it was an enlightening and breathtaking trip, which could never have been possible if we were in Singapore. Tomorrow, we will be visiting the Housing Authorities, the Coca Cola bottling plant, as well as the HK Monetary authorities. So stay tuned for more updates!
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