Cham Keng Chau 斬頸洲 (The Severed Neck of Tung Ping) EarthCache

📌 簡介 Introduction

歡迎來到香港最東端的島嶼——東平洲 (Tung Ping Chau)。這裡擁有香港最年輕的岩石（約有 5,500 萬年歷史的平洲組頁岩與粉砂岩）。而在這個島嶼的西北端，矗立著一個令人震撼的海岸侵蝕地貌景觀——斬頸洲 (Cham Keng Chau)。

從上方鳥瞰，這處景觀就像是一條巨龍被斬斷的頸部。這條寬約 4 至 8 米、長約 20 米、高約 10 米的天然海蝕峽谷，是如何在千萬年的時光中被大自然雕琢出來的呢？

Welcome to Tung Ping Chau, the easternmost island of Hong Kong. This island boasts the youngest rocks in the territory—the Ping Chau Formation (approx. 55 million years old), consisting of fine laminated siltstone and mudstone. At the northwestern tip of the island stands a striking coastal landform: Cham Keng Chau (translated as "Chop Neck Islet" or The Severed Neck of Tung Ping).

From an aerial view, it looks like a giant dragon's neck has been severed. How did this natural sea gorge, measuring about 4–8 meters wide, 20 meters long, and 10 meters high, form through millions of years of geological processing?

🧪 地質背景 Geological Background 

1. 岩石的誕生：薄層狀粉砂岩 (The Youngest Layered Siltstone)

五千多萬年前，這裡曾是一個氣候乾旱的高鹽度湖泊。微細的泥沙與火山灰在湖底一層層交替沉積，因季節與氣候變化，形成了如「千層糕」或「巨型書本」般的薄層狀粉砂岩 (Laminated Siltstone)。這些岩層以 10° 至 20° 的傾角向東北方向緩緩傾斜。

Millions of years ago, this area was a saline lake in a dry subtropical climate. Fine silt, mud, and volcanic ash deposited layer upon layer at the bottom of the calm lake. Seasonal climate variations altered the sediment composition, creating a "huge book" of tightly stacked, thin layers known as laminated siltstone. These strata dip gently toward the northeast at an angle of about 10°–20°.

2. 節理與斷裂帶 (Joints and Fracture Zones)

地殼運動強烈的擠壓力量在東平洲的岩層中震出了無數縱橫交錯的裂縫，地質學上稱為節理 (Joints)。斬頸洲原本是與主島相連的岬角，但其中心線正好坐落在一條發育完全的垂直節理或斷裂帶上。這條裂縫成為了日後風化與海水侵蝕最脆弱的突破口。

Tectonic movements and intense crustal compression created a dense network of cracks and fissures in the rock beds, geologically known as joints. Cham Keng Chau was originally a headland fully connected to the main island. However, its centerline aligned perfectly with a major vertical joint or fracture zone. This structural weakness became the prime target for weathering and wave action.

3. 海蝕峽谷的演化 (Evolution of a Sea Gorge)

斬頸洲的形成經歷了以下四個經典的海蝕地貌階段：

1. 海蝕隙 (Sea Fissure): 海浪夾雜著碎石，不斷拍擊並掏空垂直節理中的破碎岩塊，使裂縫逐漸擴大。

2. 海蝕洞 (Sea Cave): 隨着時間推移，兩側海浪從兩端同時內侵，在岬角底部掏出深入的洞穴。

3. 海蝕拱門 (Sea Arch): 當兩端的海蝕洞最終貫通時，便形成了一個頂部相連的「海蝕拱門」。

4. 海蝕峽谷 (Sea Gorge / Chasm): 隨着頂部岩層因重力與風化失去支撐而崩塌，加上地殼上升或海水面相對下降，最終留下了一條可以讓人通行無阻的平底海蝕峽谷。

The formation of Cham Keng Chau followed four textbook stages of coastal erosion:

1. Sea Fissure: Waves laden with gravel continuously pounded the vertical joint, loosening and washing away the shattered rock fragments.

2. Sea Cave: Over time, wave action from both sides of the headland hollowed out caves at the base of the weakness.

3. Sea Arch: As the caves from opposite sides breached each other and connected, a natural "Sea Arch" was formed.

4. Sea Gorge: Eventually, the roof of the arch lost structural support and collapsed due to gravity and weathering. Combined with tectonic uplift or a relative drop in sea level, a flat-bottomed sea gorge was left behind, allowing visitors to walk right through.

📋 Logging Tasks / Log 要求

要log found這個 EarthCache，請前往斬頸洲坐標處並回答以下問題。請勿將答案發表在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。

To log this EarthCache, please visit the coordinates at Cham Keng Chau and answer the following questions. Do not post the answers in 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.

1. 峽谷觀察 (Gorge Observation):
站在斬頸洲峽谷中央（兩側峭壁之間）。請仔細觀察兩側高聳的岩牆：

• (a) 兩側的垂直峭壁表面是平錶光滑的，還是凹凸不平、充滿碎石？

• (b) 你能看見明顯的水平/傾斜的「層理（千層糕紋路）」嗎？

Stand in the middle of the gorge (between the two cliffs). Look closely at the walls on both sides:

• (a) Are the surfaces of the vertical walls relatively smooth/planar, or are they jagged and filled with loose debris?

• (b) Can you clearly see the horizontal/dipping sedimentary laminations (the layered pages of the book)?

2. 寬度與測量 (Width Measurement):
請估算或測量峽谷最窄處的寬度（以米為單位）。你認為目前的潮汐海水還能在日常漲潮時輕易進入這個峽谷的中央嗎？ Estimate or measure the width of the gorge at its narrowest point (in meters). Do you think the current daily high tides can still easily flood into the center of this gorge?

3. 岩石特性 (Rock Texture):
仔細觸摸或觀察走道旁的岩石，平洲組的岩石顆粒是非常粗糙的（如砂岩、礫岩），還是非常細密平滑的（如粉砂岩、頁岩）？這反映了它當初是在激烈的海浪中沉積，還是在平靜的湖泊中沉積？ Examine the rock texture under your feet or on the walls. Are the sedimentary grains very coarse (like sandstone/conglomerate) or very fine and smooth (like siltstone/shale)? Does this suggest they were deposited in rough waves or a calm lake setting?

4. 
請以斬頸洲附近的任意地方為背景拍一張你自己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。
Take a photo of yourself with any place at Lung Lok Shui as the background, or another photo that can indicate your identity as a geocacher. This photo can be sent together with your answer or added to your log.

⚠️ Safety First / 安全至上:

Tung Ping Chau is only accessible by ferry (usually on weekends). Please check the ferry schedules carefully. The coastal rocks can be very slippery, sharp, and dangerous during high tide or rough sea conditions. Do not attempt to walk on the rocks if waves are crashing over them. Leave no trace — do not damage, chip, or remove any rock samples from this protected Geopark!

東平洲只能渡輪前往（通常在週末）。請務必仔細檢查渡輪時間表。在海水高潮或風浪較大時，海岸岩石會非常濕滑、鋒利且危險。如果海浪拍打岩石，切勿強行在前。請保持環境清潔——切勿破壞、鑿取或帶走這個受保護地質公園內的任何岩石樣本！