洞，《說文》：「空也。从穴，同聲。」
《段玉裁註》：「凡山川石穴，有空處皆曰洞。」
「洞」是中文中極富象徵性的字，代表空間、穿透、深邃。潮音洞雖非人工開鑿，卻是自然在堅硬火山岩中，歷經漫長歲月雕琢出的空間結構。而走進潮音洞，我們不只是走進一個石穴，更是走進一段地質與時間交會的縫隙。
Cave (洞), as described in the ancient Chinese dictionary Shuowen Jiezi: “An empty space. Derived from the character 穴, with a similar pronunciation.”
Scholar Duan Yucai further elaborated: “Any hollow space found in mountains, rivers, or rock formations is referred to as 洞 (cave).”
In Chinese, the character 洞 (dòng) carries deep symbolic meaning, representing space, penetration, and profundity. Though not man-made, Chaoyin Cave is a natural formation carved by time and nature into solid volcanic rock. Entering Chaoyin Cave is more than stepping into a rocky hollow, it is stepping into a crevice where geology and time converge.
The Uniquness and Geological Background of Chaoyin Cave / 潮音洞的獨特性及其地質背景
Chaoyin Cave, located on the southwestern slope of Guanyinshan in Wugu District, New Taipei City, is a unique site that blends natural scenery with religious and cultural significance. This natural cave is not only a local spiritual center but also a place of rich geological interest. Stepping into Chaoyin Cave, visitors can not only hear the echoing sounds within the cave, like the tides themselves, but also observe the textures and layers in the rock walls that reveal tens of thousands of years of geological change.
位於新北市五股區觀音山西南側的潮音洞，是一處融合自然景觀與宗教文化的獨特地點。這座天然洞穴不僅是當地重要的信仰中心，更蘊含豐富的地質意義。走入潮音洞，不僅能聆聽洞內潮音回響，也能透過岩壁紋理，讀出地層數萬年來變遷的痕跡。
Guanyinshan is a volcanic formation composed primarily of andesite, and it forms part of the Datun Volcano Group. This group of volcanoes experienced multiple eruptions between approximately 800,000 and 200,000 years ago, resulting in thick lava layers and dramatic volcanic landscapes.
潮音洞所在的觀音山，是一座由安山岩構成的火山地形，屬於大屯火山群的一部分。該火山群大約在距今 80 萬年至 20 萬年前曾多次噴發，形成了厚重的熔岩層與壯觀的火山地貌。
Andesite is an igneous rock formed by the rapid cooling of volcanic lava. It is known for its high hardness and low weathering rate, which allows it to preserve original geological features such as rock walls and caves. Due to the relatively low fluidity of andesitic magma, its lava flows tend to cover smaller areas compared to basalt. In global tectonic settings, andesite is commonly found in: 1. Island arcs, such as the Aleutian Islands in the United States. 2. Continental margins and orogenic belts, such as the Andes Mountains in Chile, often near subduction zones.
安山岩是一種由火山熔岩快速冷卻所形成的火成岩，具有高硬度與低風化性，因此容易保留原始地形特徵，常見於岩壁與洞穴的形成。由於安山岩的熔岩流動性較低，其分布範圍相對於玄武岩較小。在全球的板塊構造中，安山岩多見於：島弧地帶（如美國的阿留申群島）；大陸邊緣造山帶（如智利的安地斯山脈），常出現在隱沒帶附近。
In Taiwan, the Datun Volcano Group (located within Yangmingshan National Park) is the most prominent area where andesite is found. Here, andesite occurs in both lava flows and pyroclastic rocks, with some lava layers reaching several hundred meters thick. The formation of these volcanoes may be related to the westward extension of the Ryukyu island arc, though some scholars suggest that they were caused by crustal rifting instead.
The andesite found at Guanyinshan differs slightly from that of the Datun Volcano Group. It formed later and exhibits distinct chemical characteristics, including higher concentrations of magnesium oxide (MgO), potassium oxide (K₂O), and sodium oxide (Na₂O), indicating a unique geological origin.
在台灣，大屯火山群是安山岩最明顯的分布地區，這裡的安山岩多以熔岩流和火山碎屑岩的形式出現，有些熔岩層甚至厚達數百公尺。這些火山活動的成因可能與琉球島弧的西向延伸有關，也有學者認為是由於地殼張裂所導致。
觀音山的安山岩與大屯火山群略有不同，其形成時間較晚，且在化學成分上具有特色，如氧化鎂、氧化鉀、氧化鈉的含量較高，顯示出其獨特的地質性質。
The Classification of Natural Caves / 天然洞穴的分類
Caves (also known as caverns) are natural voids, passages, or spaces beneath the Earth’s surface. Their formation typically requires long-term geological processes such as weathering, erosion, and tectonic activity. Based on their origin and direction of formation, caves can be classified into two types:
- Exogene caves: These extend downward from the surface and usually have small openings and limited depth. Rock shelters are common examples.
- Endogene caves: These form deep underground and extend upward toward the surface. They are often more complex and extensive in structure.
洞穴（或稱洞窟）是地表下的天然空洞、通道或空間，其形成通常需要經過長時間的地質作用，例如風化、侵蝕和地殼運動。根據形成的位置與方向，洞穴可分為兩類：
- 外源洞穴（Exogene caves）：由地表向下延伸，通常開口較小、深入程度有限，例如岩棚。
- 內源洞穴（Endogene caves）：由地下深處向上延伸至地表，結構通常較為複雜且深入。
Natural caves can be classified based on the processes that formed them:
天然洞穴可依其形成原因分類為以下幾種：
🔹 Solutional Caves (Limestone Caves) / 石灰岩洞
Also known as karst or stalactite caves, these caves are formed when rainwater or groundwater dissolves and erodes layers of limestone. Calcium carbonate in the rock dissolves in water, and over time, this erosion creates underground voids. Some of the dissolved minerals later precipitate, forming stunning formations such as stalactites and stalagmites.
石灰岩洞又稱溶洞或鐘乳石洞，主要由雨水或地下水溶解與侵蝕石灰岩層而形成。石灰岩中的碳酸鈣會被水溶解帶走，經長時間侵蝕與沉積後，地下岩層逐漸形成空間。部分溶解於水中的鈣質會再次沉澱，形成鐘乳石、石筍等特殊地質景觀。
🔹 Lava Caves (Primary Caves) / 熔岩洞
These caves form at the same time as the surrounding volcanic rock. When lava flows during a volcanic eruption, the outer layer cools first, creating a solid crust, while the interior lava continues to flow. If the lava inside drains away, a hollow tunnel or tube is left behind.
當火山熔岩流動時，外層先冷卻形成硬殼，內部熾熱的熔岩仍持續流動。若內部熔岩完全流出，外層硬殼就會留下隧道狀或管狀的中空結構。這類與周圍岩層同時形成的洞穴，稱為原生洞（Primary caves）。
🔹 Sea Caves / 海蝕洞
Formed by the mechanical action of ocean waves, sea caves occur along rocky coastlines. The force of waves, combined with sand and gravel carried in the water, erodes the base of coastal cliffs. This undercutting can cause the overlying rock to collapse, forming a sea cave.
海蝕洞是海水侵蝕岩岸所形成的。波浪衝擊加上水中砂礫的摩擦，會侵蝕海岸坡腳，導致上方岩石崩落，進而形成洞穴。
🔹 Erosional Caves / 風化洞（侵蝕洞）
Also known as weathering caves, these are created by flowing water, wind, or biological processes that carry sediments and wear away rock. Erosional caves can form in many types of rock, including hard rocks like granite, typically along weaker zones such as joints or faults.
風化洞是由攜帶岩石與沉積物的水流、風力或生物作用所造成的風化與侵蝕作用所形成。這類洞穴可出現在各類岩石中，包括堅硬如花崗岩的岩體。通常沿著節理或斷層等岩層中的薄弱處開始形成。
🔹 Glacial Caves / 冰河洞
These caves form beneath or within glaciers due to melting ice and flowing meltwater. The slow movement of the glacier can deform or collapse the cave over time.
冰河洞是因冰河底部融水流動或冰層內部融化所形成，冰層的緩慢運動可能導致這些洞穴產生變形或坍塌。
🔹 Fracture Caves / 裂隙洞
Formed when differences in mineral solubility or tectonic activity cause rock layers to fracture or collapse. These caves typically develop along faults or cracks in the rock.
當岩層中礦物的溶解性差異或地質活動造成岩石斷裂與崩塌時，可能會形成裂隙洞。這些洞穴多沿裂縫或斷層發展。
To log this cache, please visit Chaoyin Cave, observe carefully, and answer the following questions:
- Based on your observation, what type of cave do you think Chaoyin Cave is, exogenous or endogenous? Please explain your reasoning.
根據你的觀察，你認為潮音洞是外源洞穴還是內源洞穴？並請說明你的判斷依據。
- Based on what you see at the site, what do you think caused the formation of Chaoyin Cave?
Classify the cave according to its formation process (e.g., solutional cave, lava cave, sea cave, etc.), and explain your conclusion.
根據你在現場的觀察，請推測潮音洞的成因為何？
請依照其形成原因對潮音洞進行分類（例如：溶蝕洞、熔岩洞、海蝕洞等），並說明你的判斷依據。
- Take one or more photos inside the cave that support your answers to Questions 1 and 2. Please send these photos along with your answers to me.
作為第 1 和第 2 題的依據，請拍攝一張或多張洞內照片，並與你的答案一併傳給我。
- (Optional) Take a photo of yourself, or an object that represents you, inside Chaoyin Cave.
Notes:
- Please don’t post any answers in your log.
- Only the accounts that sent the answers could log as found, so please make sure you sent your own answers even you’re in the group-hunting.
- You MUST visit the earthcache location to claim a find. I’ll delete the logs of people who clearly didn’t visit the earthcache or who didn't complete the logging tasks.
- You don’t have to wait the permission to log after you send the answers. Any logs without all of the answers will be deleted.
REF: Wikipedia, 臺灣地質知識服務網