此地球藏寶點展示火山熔岩如何凝固成岩石、冷卻過程如何形成天然裂隙，以及玄武岩如何在噴發結束後長期保存地球火山活動的證據。
玄武岩——凝固於岩石中的熔岩
玄武岩是玄武岩的裸露表面，這種深色火成岩由噴發至地表的熔融岩漿形成。作為地球上最常見的火山岩，玄武岩構成了大部分海洋地殼，以及眾多火山高原與島嶼。
玄武岩形成於低黏度岩漿自地幔上升並噴發為熔岩時。由於此類熔岩流動性強，能長距離移動並擴散成廣闊的薄層岩流，而非堆積成陡峭的火山錐。當熔岩流經地表時，會逐漸冷卻凝固，形成緻密細粒的岩石。
玄武岩冷卻時會收縮，這種收縮作用會形成稱為冷卻節理的裂隙。這些節理常形成筆直或呈角狀的裂縫，將岩石分割成板狀、塊狀或多邊形紋理。在某些地區，反覆的熔岩流層層堆疊，形成層狀玄武岩板，如今在侵蝕作用移除覆蓋物質後，這些岩層仍可被觀察到。
玄武岩板層亦保存了熔岩尚未凝固時的特徵：熔岩中困住的氣泡會留下稱為氣孔的小孔洞，而流動紋理如細微脊狀或表面皺褶則可能顯示熔岩的流動方向。缺乏大型可見結晶的現象，表明熔岩是在地表或近地表區域快速冷卻形成的。
隨著時間推移，風化與侵蝕作用使裂隙擴張、岩板分離，使其更為顯著。水流、溫差與生物活動雖會緩慢分解岩石，但玄武岩的硬度使其板塊能長期保持完整，清晰保存火山作用的證據。
在此地球藏寶點，裸露的玄武岩板塊為人們提供了直觀的地球火山史窗口，展現熔融岩漿如何凝固、斷裂，並以固態岩石形式存續數百萬年之久。
現場觀察要點
玄武岩屬火山岩
由熔岩流形成，非地下岩漿
因急速冷卻形成細粒結構
冷卻收縮形成板狀岩體
裂隙常呈直線、角狀或塊狀
可能含有火山氣體形成的氣孔
典型色澤為深灰至黑色
要記錄此地球寶藏，
您必須親臨現場並回答與地球寶藏坐標相關的問題。
收集答案後，請將其提交給管理員進行核驗。
提交答案後即可立即記錄。若管理員對您的答案有疑問，將主動聯繫您。
未向管理員提交解答或存在待處理問題的記錄將被刪除，恕不另行通知。
請勿在記錄中附上可能透露問題答案的照片。
問題
1. 請前往指定座標點回答以下問題：
A. 描述您觀察到的玄武岩顏色與質地。是否可見單一礦物結晶？
B. 玄武岩的斷裂形態如何？呈現平整、塊狀、階梯狀，或碎裂成幾何形狀？其結構特徵為何？
C. 根據觀察結果，你認為這塊玄武岩是在地表快速冷卻還是地下緩慢冷卻形成的？請運用可見證據說明你的推論。
2. 請拍攝你本人、小組成員或GPS設備在該地點的照片，但不得透露任何答案內容。
This EarthCache demonstrates how volcanic lava becomes solid rock, how cooling creates natural fractures, and how basalt preserve evidence of Earth’s volcanic activity long after eruptions have ended.
Basalt – Frozen Lava in Stone
Basalt are exposed surfaces of basalt, a dark-colored igneous rock formed from molten lava that erupted at Earth’s surface. Basalt is the most common volcanic rock on Earth and makes up most of the oceanic crust as well as many volcanic plateaus and islands.
Basalt forms when low-viscosity magma rises from the mantle and erupts as lava. Because this lava is fluid, it can travel long distances and spread out into broad, thin flows rather than building steep volcanic cones. As the lava flows across the landscape, it gradually cools and solidifies, forming a dense, fine-grained rock.
As basalt cools, it contracts. This contraction creates fractures known as cooling joints. These joints often form straight or angular cracks that divide the rock into slabs, blocks, or polygonal patterns. In some locations, repeated lava flows stack on top of each other, creating layered basalt slabs that can be observed today where erosion has removed overlying material.
Basalt slabs also preserve features that formed while the lava was still molten. Gas bubbles trapped in the lava may leave behind small holes called vesicles, and flow textures such as subtle ridges or surface wrinkles may indicate the direction the lava once moved. The absence of large visible crystals shows that the lava cooled relatively quickly at or near the surface.
Over time, weathering and erosion widen fractures and separate slabs, making them more visible. Water, temperature changes, and biological activity slowly break down the rock, but basalt’s hardness allows slabs to remain intact for long periods, preserving clear evidence of volcanic processes.
At this EarthCache location, the exposed basalt slabs provide a direct view into Earth’s volcanic history, showing how molten lava can solidify, fracture, and persist as solid rock for millions of years.
Key Facts to Observe On-Site
Basalt is an extrusive igneous rock
Formed from lava flows, not underground magma
Fine-grained texture due to rapid cooling
Slabs form from contraction during cooling
Fractures often appear straight, angular, or block-like
May contain vesicles from trapped volcanic gases
Dark gray to black color is typical
To log this cache.
To get to log this cache you will have to visit and answer the questions which are related to the coordinates given the earthcache.
When answers are collected, send them to CO for verification.
You can log immediately after answers are sent CO. If there are any questions about your answers CO will contact you.
Logs without answers to CO or with pending questions from CO will be deleted without any further notice.
Please do not include pictures in your log that may answer the questions.
Questions
1. Answer the questions by visiting the coordinates.
A. Describe the color and texture of the basalt stone you observe. Are individual mineral crystals visible?
B. How are the basalt stone fractured? Do it appear flat, blocky, stepped, or broken into geometric shapes? And what is its structures?
C. Based on what you observe, do you think this basalt cooled quickly at the surface or slowly underground? Explain your reasoning using visible evidence.
2. Take a photo of you, the group or the GPS from the location without revealing any of the answers.