7/2/20 - 我添加了中文翻譯...請參閱下文。

This EarthCache examines a type of coastal erosion, specifically resulting in the formation of wave-cut platforms. It leads you to the famous formation “Little Taiwan” on Qimei (Chimei) Island in Penghu County. The learning point of this EarthCache is to get the geocacher to become familiar with the formation of wave-cut platforms.

Everything you need to answer the questions is available by visiting the location and by reading this lesson. I don’t anticipate you will have to research anything extra online, although you’re welcome to do so if you wish to.

Location of Qimei Island

At the listed coordinates you will find yourself overlooking “Little Taiwan.” This is one of the many geological wonders of Qimei Island, and is one of the highlights of any trip to the island.

Please be aware this EarthCache should only be attempted from the safety of the posted coordinates - it is dangerous to try to get anywhere closer to the formation itself. Also, please be careful around the cliff edge and stay on the marked paths, for your own safety. 

Little Taiwan is only visible at low tide, so please check the tide times before you come to avoid disappointment. 

Tide times are available here: https://www.tideking.com/Taiwan/Taiwan/Penghu/Qimei-Yu-Dengta/

Little Taiwan can be found on the west coast of Qimei Island

Little Taiwan is so called because it resembles the shape of Taiwan Island. In fact, it is said to be 99% similar to the main island. Geologically speaking, Little Taiwan can be referred to as a wave-cut platform. It is not just a beautiful location and Penghu geological must-see; it is the best example of this type of formation in the country.

A wave-cut platform is a flat area of rock that projects towards the sea from the base of sea cliffs. They are created by the process of erosion, using the tidal energy of the waves. Wave-cut platforms are usually only visible at low tide as huge expanses of flat rock. 

A wave cut platform is formed when a notch is formed at the base of cliffs by attrition. (Attrition is when rocks that the sea is carrying knock against each other, or against the developing wave cut platform.)As time goes on, the notch gets bigger and the cliff collapses as its weight can no longer be supported. The chalk platform is left just a bit higher than the sea bed.

Wave erosion of cliffs is caused by the energy of many tonnes of water repeatedly striking the rock with great force over long periods of time.The energy produced by the waves compresses the air within the joints of the rocks which results in the widening of the joints. At the same time, the wave energy also moves broken rocks, sand and other particles against the eroded surfaces which results in scour erosion. Over time, the wave energy cuts deeply into the cliffs, undercutting the rocks above, and resulting in the formation of a notch. The overhanging rock collapses, which results in retreating cliffs and wave-cut platforms.

This diagram summarises the formation of wave-cut platforms such as Little Taiwan

As with the rest of Penghu, most of Qimei Island consists of basalt and andesite plutonic formations. Radioactive dating shows that Qimei had already taken primitive form 8 million to 17 million years ago, and wave erosion and weathering in the eons since have given the island the unique topography we see today. 

On Qimei Island, Pleistocene fissure eruptions produced a widespread flood basalt. It is thought that this basaltic volcanic stage probably occurred towards the end of the main orogeny in Taiwan. (Orogeny is the process whereby mountains are formed on continental plates.) Recent unpublished studies, however, have reported that the Penghu basalt may be of Miocene age on the evidence of K-Ar dating and the contained foraminiferal fossils.In the Pleistocene era, the movement of tectonic plates created cracks in the Earth’s crust, allowing high pressure to force hot lava to the surface through these fissures, where in the air and the water it gradually cooled and hardened. As it cooled, molten rock hardened and formed the islands you see today. Scientific dating of this basalt rocks, as well as on organic deposits in the smaller proportion of sedimentary rocks on the island, reveal that the volcanic activity was from Middle Miocene to Late Miocene. On Qimei Island, the Pleistocene plateau basalt was extruded from fissures in the Late Cenozoic strata. Extensive basaltic flows cover the entire island group except one southwest islet, forming typical mesa-type landforms. Regarding the sedimentary rocks that can be found deposited upon the older basalt underneath, Qimei Island is covered by flat-lying Neogene sediments. The thickness of these Neogene sequence is much less than that found on Taiwan proper. This explains why basalt formations on Qimei, including the Little Taiwan wave-cut platform, are often more exposed and regularly visible on Qimei than on Taiwan itself.

The wave-cut platform in front of you consists of hard and resistant basalt stone. This is the older, original rock that formed Qimei Island, before sedimentary deposits lithified upon it over the millennia. Wave erosion along horizontal to gently dipping bedding planes (the sedimentary layers) results in the flat to gently sloping surface of the wave-cut platform. You will also notice vertical intersecting joints (cracks in the rock) in front of you. These are areas of weakness within the rock where, through the process of erosion, rectangular rocks ‘break off’. These joints control the shape and orientation of the platform margins.

Over the last 2 million years, the sea level has risen and fallen as the Earth’s temperature has increased and decreased. During the colder glacial periods, when massive ice sheets froze much ocean water, sea levels were significantly lower. During the warmer interglacial periods the ice sheets melted, and so the sea level rose. The last colder period occurred about 18,000 years ago when the Earth was in the last peak of glaciations. At this time, the sea levels were around 120 metres lower than they are today.

As this cold period ended and the Earth entered it’s current, warmer period, sea levels rose. The rising sea levels flooded the valleys and crept up the hillsides. Wave-cut platforms like Little Taiwan began forming around 6,500 years ago, when the sea reached its modern day level. The continued wave action eroded cliffs.

To log this cache, please visit the published co-ordinates and answer the questions below. Once you have obtained the answers, please send them to me via email or through the Message Centre. You are free to log your find once you have contacted me. You don't have to wait for a reply. If there are any questions about your answers, I’ll contact you.   

Logs without answers will be deleted. Please don’t include close up pictures in your logs that may answer the questions.  

Questions:

1 Look at Little Taiwan. What is it’s approximate size?

2 Look at the surface of the wave cut platform. Please describe it (colour, texture, features, etc.)

3 What is the approximate height of the top of the cliff, where you are now, to the sea level below?

4 Other than the power of the waves, can you identify any other factors that may be affecting the rate of erosion here?

5 Look across at the cliffs to either side of Little Taiwan. Identify the different layers of igneous and sedimentary rock. Which is thicker? Measure this thickest layer and try to explain why this layer is the thickest.

6 Look at the ground beneath your feet. Are the clifftops here sedimentary or igneous rock? Why do you think so?

7 With reference to the lesson, and your answers to question 2, what might you expect to happen to the wave cut platform and immediate surrounding area in the future?

8 Optional, take a photo of yourself and/or your GPS in the general area of this EarthCache.  

Good luck, and thanks for visiting this EarthCache!

中文：

這個地理藏寶要帶您認識一種海蝕地形，這種侵蝕現象形成了海蝕平台。 此地理藏寶 會帶您到澎湖縣七美鄉有名的小台灣景點。此項地理藏寶的學習重點在於讓尋寶者熟 悉海蝕平台形成背後的原因。

只要造訪此地以及研讀此課程，您就能獲得回答問題所需具備的一切知識。我不期待 大家另外在網路上查資料，當然如果您 想要，歡迎這麼做。

七美島的位置

在列出的座標上您可以俯瞰小台灣。這是七美島眾多地質奇觀中的其中之一，也是到

島上旅遊時最精彩的觀光景點其一。

請注意只能從張貼座標的安全之處嘗試獲取此地理藏寶。想要從任何地方接近此地理

藏寶都是相當危險的。此外，在懸岩邊請小心，為了自身的安全盡量停留在有標記的

路徑上。

小台灣只有在低潮時看得見，請記得先查好潮汐表再前往觀看，以免敗興而歸。 潮汐表可至此網址觀看

here: https://www.tideking.com/Taiwan/Taiwan/Penghu/Qimei-Yu-Dengta/

小台灣位於七美島的西海岸

小台灣的命名是由於其外型看似台灣島。事實上，據說其與台灣本島的相似度高達百 分之 99。從地質上來說，小台灣是一種海蝕平台。它不僅是個美麗的景點，也是造訪 澎湖地質奇觀必去之處。在台灣它也是此類地形的最佳範例。

海蝕平台是一塊平坦的岩石，從海岸懸崖的底部向大海延伸。它們是藉由海浪潮汐力

量侵蝕所形成的。海蝕平台通常只有在低潮時看得見，外型是大片平坦的岩石。

海蝕平台的形成是由於懸崖底部磨損而形成 V 形槽口。海浪挾帶著岩石彼此撞擊也與 逐漸形成的海蝕平台撞擊，這就是磨損的原因。隨著時間的流逝，V 形槽口越來越 大，懸崖的重量失去底部支持力因此坍塌。留下的平台高度比起海底稍微高些。

懸崖的海浪侵蝕作用是由於數噸的海水長時間重複不斷強力撞擊岩石所造成的。海浪 所產生的力會壓縮岩石縫隙內的空氣，造成縫隙擴張。在此同時，海浪的能量也能搬 運破碎的岩石、沙子以及其他的顆粒至侵蝕的岩石表面上，導致沖刷侵蝕。隨著時間 的推移，海浪的力量能在懸崖上切割出深縫並削弱上方的岩石，V 形槽口也因此生 成。懸吊著的岩石坍塌，導致懸崖後退並形成海蝕平台。

這張表簡要的概述了像小台灣此類的海蝕平台形成的過程。就像澎湖多數地形一樣， 七美島的地質是由玄武岩和安山岩等火山岩所組成的。放射性年代測定顯示七美在 800 萬至 1700 萬年前已形成其原始的雛型。\隨著漫長的歲月流逝，海浪的侵蝕和風化 作用使該島形成了我們今日所見的獨特地形。

在七美島上有更新世的玄武岩，從裂隙所噴發的岩漿形成了四處可見的洪流式玄武 岩。一般認為此玄武岩火山活動大約發生於台灣主要造山運動的晚期。(造山運動指的 是大陸板塊上山脈形成的過程。) 然而，近期未發表的研究顯示根據鉀氬年代測定法與 岩石中所含的有孔蟲化石等證據，澎湖的玄武岩可能來自第三紀中新世。在更新世時 期，板塊運動在地殼形成了裂縫，在高壓的驅使之下高溫的岩漿透過這些裂隙流至地 表並在空氣與水中逐漸地冷卻凝固。岩漿冷卻後熔融的岩石硬化並形成人們今日所見 的島嶼。根據玄武岩的科學年代測定以及島上小部分沉積岩內的有機沉澱物，火山活 動時間是從中新世中期到到中新世晚期。七美島上的更新世高原玄武岩是從新生紀晚 期的地層縫隙中擠壓形成的。除了西南方的一個小島外，玄武岩流廣泛地覆蓋了整個 群島，形成了典型的方山地貌。以沉澱在地底下較舊玄武岩之上的沉積岩而言，七美 島上覆蓋著平伏的新第三紀沉積物。相較於在台灣所發現的新第三紀序列沉積物，此 處的厚度較小。這也解釋了為什麼相較於台灣本島，七美島上的玄武岩包括小台灣的 海蝕平台在內較常暴露在外且目視可見。

在您前方的海蝕平台是由堅硬且抗壓的玄武岩組成。七美島是由這些較老的原始岩石 所形成，接著經過一千年的時間，沉積物在這些原始岩石上固化。海浪沿著水平面稍 微下凹的岩層(沉積岩層)進行侵蝕，使得岩層平面形成些微傾斜的海蝕平台。 您可以注意到前方垂直相交的接口(岩石中的裂縫)。經過侵蝕作用的過程，這些矩形 岩石斷裂之處就是岩石結構中的脆弱區域。這些接口能控制平台邊緣的外型與方向。

在過去的 2 百萬年間，由於地球溫度的增加與減少，海平面也跟著上升下降。在寒冷 的冰河時期，大量的冰川凍結了很多海水，海平面明顯地較低。在較溫暖的間冰期， 冰川融化，海平面因此而上升。上一次較冷的時期大約發生在 18000 年前，當時地球 正處於冰川期最後的高峰期。相較於今日，當時的海平面比現在低 120 公尺左右。

隨著這段低溫時期結束後，地球進入現在較為溫暖的時期，海平面也跟著升高。 海平面上升淹沒了山谷與山坡。像小台灣這樣的海蝕平台在大約 6500 年前開始成形， 當時海平面已與現代的高度一樣。海浪運動持續地侵蝕懸崖。

若您想紀錄此地理藏寶，請造訪此發布的座標並回答下列的問題。一旦您獲得答案，

請藉由電子郵件或訊息中心將答案傳給我。只要您聯繫我了，就可以將此藏寶紀錄

下，不需要等待我的回覆。如果您的答案有任何問題，我會與您聯絡。

沒有附上答案的紀錄將會被刪除。請勿在您的紀錄裡附上能提供解答的近距照。 問題:

1. 看看小台灣，它的大小約略是多少?

2. 看看海蝕平台的表面。請描述一下它的外觀(顏色、結構、特色等等。)

3. 懸崖頂端也就是您現在所站的地點距離下方海平面大概高度多少?

4. 除了海浪的力量外，您能不能辨認出這裡其它可能會影響侵蝕速率的因素?

5. 看看小台灣懸崖的兩邊。試著去辨認出不同層的火成岩與沉積岩。哪個比較厚

呢?測量最厚的岩層並試著解釋為什麼這邊的岩層是最厚的。

6. 看看您腳下的地面。懸崖頂部的地面是沉積岩還是火成岩呢? 您的看法是甚麼

呢?

7. 參考前面的課程內容以及您第二題的答案，您期待未來海蝕平台及周遭的環境 會有甚麼變化呢?

8. 您可以自行選擇是否要在此地理藏寶的大略位置拍張有您和 GPS 的照片，或只 含有 GPS 的照片。

祝您好運，感謝您前來造訪此地理藏寶!