Explanation and evaluation

First of all, there are mainly internal process include faulting and vulcanicity affect the relief of Cheung Chau.

In Nam Tam Wan, Southern tip of Cheung Chau, we can find that there is a pale pink dyke.(reference#3) But common dykes in Hong Kong are usually dark in colour. According to the book-Rocks and mineralsp. 30 (reference#10), it says that it is a granite dyke due to the solidification of cooled magma. It is paler than the surrounding granite bedrock because it may be the earlier dyke that appear on the ground and undergone serious weathering and erosion in hot and wet climate.

Referring to the map (reference#6), Cheung Chau is mainly formed by two granitic islands in the northern and southern part. Granite is a kind of intrusive igneous rocks. Which magmarises along the cracks to the earth's surface, then cools and solidies. During the cooling process, crystallized minerals group together and appear interlocking with each other. (reference#2). The three major minerals are quartz, mica and feldspar. Their size are relatively large and most of them are coarse-grained. Granite is an acidic rock, it has a high silica content. So theat its colour tends to be lighter. A batholith is a larger mass of intrusive rock formed deep underground. It is formed by the cooling of magmka that accumulates at a deep dome-shaped chamber. In Hong Kong, exposed batholiths cover over one-third of the area. They became exposed after the rocks on top were removed from erosion.

As granite is less resistant under hot and wet climate, it is therefore subject subject to serious weathering and erosion. Low hills with relatively gentle slopes and rounded peaks are formed. As I mentioned before, Cheung chau's relief is tend to be lower. Dykes and faults in Cheung Chau is mainly located at the southern and northern part of Cheung Chau.

Second, there are external process such as weathering, erosion and mass movement affect the relief of Cheung chau.

First of all, there are three types of weathering, which are mechanical weathering, chemical weathering and biological weathering.

We have found that mechanical weathering of block disintegration of rock in Cheung Chau, and it usually occurs in well-jointed rocks.

There are two forms of chemical weathering, which are honeycomb weathering and spheroidal weathering.

Let's take an example of honeycomb weathering , human head rock made up by quartz, feldspar and plagioclase. Among them, feldspar and plagioclase are the easiest to be eroded. Human head rocks formed by the process of honeycomb weathering, which is exposed in the open area and the coast, feldspar and plagioclase in the rock dissolved and carried away by rain water and the splashes of sea water or solution. Through all the year round with weathering and erosion, the shape and the arrangement of a small hole look like honeycomb.(#6)

In Cheung Chau, the notch inside may present many cracks. These cracks and joints are results of biological weathering. The roots of living plants may penetrate into the joints of well-jointed tock, causing them to enlarge. These roots on living plants may secret some organic acid, causing solution, hydration.(#5)

From above, there are mainly mechanical weathering and chemical weathering in Cheung Chau. In Cheung Chau field trip, there are many this types of rocks on the way. Moreover, mechanical weathering and chemical weathering usually work together and shaped the rock and the relief of a place efficiently.

Next, we would like to talk about water erosion and fluvial and coastal erosion in Cheung Chau.

Splashes of heavy rain can loose and move soil. During the rainy season, rainwater running down the wall of the cracks removes the soil grains, this thus formed rill erosion. When rill joins up and become deeper and wider channelss, gullies erosion is formed. Meamtime, gully erosion removes soil downslope, and itfinally lead to soil erosion. Furthermore, badland is formed if there with dense concentration of gullies.(#2) In Cheung Chau, they're found on the northern island.

Fluvial and coastal erosion refers to the erosion of rock materials from river banks and river bads. Along caost, erosion is brought about by waves and tides.(#2) For instant, there is a rock called turtle rock in Tung Wan Beach in Cheung Chau, which stays lonely in the sea of the beach.(#1)

From above, water erosion and fluvial and coastal erosion really pay an important role to shape the rock and the relief of Cheung Chau, because Cheung Chau is an offshore island, which means it is sounded by sea, and the rocks are easy eroded by waves and tide, etc. the examples are vase rock, seal rock and so on.

Finally, we would like to talk about mass movement include landslide and rockfalls in Cheung Chau.

Landslide is a kind of fast movement by which rocks and soils of all sizes collapse through either sliding or slumping along a curved surface.(#2)

Rockfalls refer to the free fall of rock fragments ranging from samll grains to huge blocks from steep or overhanging slopes. Partially weathered rocks may loose support and fall due to gravity. Rockfall is a sudden and very fast movement.(#2)

From above, we know that landslides and rockfalls are common phenomenon on slope. In 2006, there were landslides and rockfalls in Cheung Chau, and we can see that the preventive measures agencies there and so there were landslides taken in Cheung Chau. As the steeper the slope, the more serious the landslides and rockfalls, the higher the relief of a place. The more gentle the slope in Cheung Chau, the less serious the landslide and rockfalls, the lower the relief in Cheung Chau. As a result, we can prove that Cheung Chau's relief is quite low.