一、簡介
鴨洲位於香港新界東北印洲塘與沙頭角海交界處，距北面的深圳鹽田港不到2公里。由西北面望去，島嶼的形狀就像一隻在海上暢泳的鴨子，因此得名鴨洲。全島只有0.04平方公里，建有一條漁民村，面積雖小，卻有三「最」：是香港有人居住的最細小島嶼、出露香港罕見的褐紅色角礫岩，以及擁有香港唯一可以安全徒步穿越的海蝕拱。鴨洲島上設備齊全，有可供遊船停泊的碼頭，亦有漁民自建的學校，全盛時期有過千人居住。其後，年青一輩為改善生活，到海外謀生，而留港村民亦因工作關係，或遷就子女求學，紛紛搬遷到市區居住。
二、海浪的侵蝕力量
風浪是海岸最強大的力量，海浪夾雜沙石，有如巨大的打磨機，不停打磨海岸的岩石。
海岸石層構造中較為薄弱的位置在海浪浸蝕下易於凹陷，形成海蝕洞或海蝕凹槽。
隨著海浪繼續沖刷和侵蝕，這些洞穴或凹槽上面的岩石會因為失去底部支撐而倒塌，留下一堵陡崖，稱為海蝕崖。
海蝕過程不斷重複，海蝕崖亦逐漸向內陸發展，留下一個貼近海平面的平台，稱為海蝕平台。
在海浪不斷侵蝕下，海角兩側的海蝕洞/海蝕凹槽貫穿，形成穿孔狀態；孔洞上面的岩層狀如天然石拱橋，名為海蝕拱。
三、Log 要求
發布地點位於海蝕拱(鴨眼)旁。
- 看著海蝕拱，試估算海蝕拱的長、寬、高。
- 試參考上述海蝕拱的描述，以及在發布地點附近的觀察所得，試解釋鴨洲的海蝕拱形成的原因。
- 請以海蝕拱為背景，拍一張你自己的照片或其他能表明你藏寶者身分的照片。這張照片可以與答案一起發送給我，也可以添加到你的log中。
透過 geocaching.com 的訊息中心系統將答案發送給我後，你可以直接log found此藏寶，無需等待我的確認。如果你的答案有任何問題，我會通知你。
1. Introduction
Ap Chau is an island in the northeast New Territories, where Double Haven meets Starling Inlet. It is less than 2 km from Shenzhen’s Yantian Port to the north. Viewed from the northwest, the shape of the island resembles a duck swimming in the sea; hence, its name, Duck Island (Ap Chau in Cantonese). Although just 0.04 km2 in size, Ap Chau has a fishing village and at least three special features: it is the smallest inhabited island in Hong Kong; it is home to locally rare ochre breccia; and it is the site of Hong Kong’s only sea arch that is safe to walk through. Ap Chau is well supplied with facilities, such as a pier for berthing, a school established by fishermen, etc. During the most prosperous period, more than a thousand people were living there. Later on, the youth moved overseas to improve their living, whereas the others also moved out to urban area for better jobs or better schools for the children.
2. The Power of Wave Erosion
Wind and waves are the most powerful erosion forces in coastal areas. Waves loaded with sand and gravel act like a huge grinding machine, constantly pounding coastal rocks.
The weaker part of the rock strata along the coast is prone to forming depressions, known as sea caves or sea notches, due to erosion.
The continuous splashing and erosion by waves erodes the base, resulting in the rock above the caves or notches collapsing, leaving behind a steep rock face, called a sea cliff.
As the wave-erosion process is repeated, a sea cliff gradually develops inland, leaving a platform close to sea level, called a wave-cut platform.
In certain circumstances, the sea cave or sea notch penetrates all the way through the cape, and the rock strata above the penetration resemble a natural stone arch, known as a sea arch.
3. Logging tasks:
- Looking at the sea arch, try to estimate its length, width, and height.
- Based on the description of the sea arch above and observations made near the posted coordinate, explain the reasons for the formation of the sea arch at Ap Chau.
- Take a photo of yourself with the sea arch as the background, or another photo that can indicate your identity as a treasure seeker. This photo can be sent together with your answer or added to your log.
You can log this cache without waiting for my confirmation, but you must send me the answers at the same time, by the system of Message Center of geocaching.com. If there is a problem with your answers I will notify you.
References:
https://running.biji.co/
https://www.geopark.gov.hk/tc