噴出地表後，就開始冷卻凝固。冷卻時，在岩漿的上面會產生許多的收縮中心，依當時環境的溫度，氣溫低冷時，收縮中心就會越密集，反之則收縮中心的距離就會變大。而玄武岩的節理就由兩兩收縮中心往下延伸產生裂痕，如同泥裂一般，這就是玄武岩的柱狀節理。結晶過程中，由於岩漿收縮而裂開成多邊形的柱狀體。柱狀體的形狀從四邊形到八邊形都有，其中以五邊形和六邊形為最多。其節理方向是垂直於熔岩流溫度的分佈方向，藉由柱狀體的節理，可幫助我們判定此一熔岩的產狀。柱狀體有粗有細，構造的方向有垂直、水平、傾斜和扇狀等形狀，其中垂直方向大都是噴出地表的熔岩所形成；水平方向則可能是侵入的岩體所形成；而傾斜和扇狀則侵入和噴出兩者皆可形成。七美西北灣的柱狀節理是澎湖玄武岩中最壯觀的柱狀景觀。本中心收藏之標本採集自白沙通梁、白沙嶼、西嶼大菓葉等地。
噴出地表後，就開始冷卻凝固。冷卻時，在岩漿的上面會產生許多的收縮中心，依當時環境的溫度，氣溫低冷時，收縮中心就會越密集，反之則收縮中心的距離就會變大。而玄武岩的節理就由兩兩收縮中心往下延伸產生裂痕，如同泥裂一般，這就是玄武岩的柱狀節理。結晶過程中，由於岩漿收縮而裂開成多邊形的柱狀體。柱狀體的形狀從四邊形到八邊形都有，其中以五邊形和六邊形為最多。其節理方向是垂直於熔岩流溫度的分佈方向，藉由柱狀體的節理，可幫助我們判定此一熔岩的產狀。柱狀體有粗有細，構造的方向有垂直、水平、傾斜和扇狀等形狀，其中垂直方向大都是噴出地表的熔岩所形成；水平方向則可能是侵入的岩體所形成；而傾斜和扇狀則侵入和噴出兩者皆可形成。七美西北灣的柱狀節理是澎湖玄武岩中最壯觀的柱狀景觀。本中心收藏之標本採集自白沙通梁、白沙嶼、西嶼大菓葉等地。
After being ejected out to the surface, the lava begins to coolsolidify. During cooling, many shrinkage centers are generated on the top of the lava according to the temperature of the environment at the time. When the temperature is lowcold, the distance between the shrinkage centers are denser, otherwise the distance between the shrinkage centers become larger. The joints of basalt extend downward from the two shrinkage centers to produce cracks, like mud cracks, which are columnar joints of basalt. During the crystallization process, the lava shrinkssplits into polygonal columns. Cylinders vary in shapes ranging from quadrilateral to octagonal forms, with pentagonshexagons being the most common. The joint direction is perpendicular to the distribution direction of lava flow temperature. The joints of the columnar body can help us determine howwhere the lava has erupted. The columnar body can be thickthin,the direction of the structure can be vertical, horizontal, inclinedfan-shaped. Among them, the vertical direction is mostly formed by the lava extruding out of the earth surface the horizontal direction may be formed by the intrusive rock mass,the inclinedfan-shaped directions can be formed by both intrusiveextrusive rock masses. The columnar joints of Qimei Northwest Bay are the most spectacular columnar landscapes in Penghu basalt. The specimens collected by this center are from Paisha Township’s Tongliang, Paishayu,Siyu’s Daguoye.
