火山活动是否波动,而取决于你正在看的时间尺度。[脆(1984)][1]编译可用数据对火成岩活动持续了超过300年,得出结论:在过去的1.8亿年里年均岩浆输出每年约30公里<一口> 3 < /一口>,其中~ 75%是产生在大洋中脊。最明显的变化在输出岩浆起源于洪流玄武岩喷发,结果经常与大陆裂谷作用有关,建议从第一个新的热上涌地幔柱的影响。这些是巨大的事件——大约10 <一口> < /一口> 6公里<一口> 3 < /一口>岩浆侵位时间尺度短一百万多年,总是不到1000万年,虽然他们占>陆内火山活动的95%,他们只占大约5%的全球岩浆输出由于其罕见。所以,是的,在短时间尺度上火山活动可以和波动,输出率通常较高而大火成岩省侵位正在进行——实际上很长时间尺度(如果地球是在其早期历史中岩浆海洋,它有更多的火山活动比现代表面!)。然而,在媒介时间表-地质学家通常感兴趣的平均输出率相当稳定。(已经提到)[2][关于地震][3],地震是增加在频率。要点,与地震、改进技术和人口密度增加。江南登录网址app下载人口密度的增加会更多的被观测到的事件,事件和个人有更大的负面影响;科技的进步,更容易执行远程观察,江南登录网址app下载和识别远程爆发在地质的过去。 In particular, work with Antarctic ice cores (we have records going back 800,000 years at this point, and work is ongoing on a million-year core!) allow identification of discrete eruptions because they deposit layers of fine ash or, from further away, acid-rich layers. These eruptions can be correlated with one another between different cores - and even ice cores taken from different continents - through massive "marker" eruptions, such as Krakatoa, and to some extent through absolute dating via isotope chemistry in air bubbles trapped within the ice. However, even as our ability to interpret ice cores further and further back improves, our estimates of global magmatic activity stay pretty constant: despite being published 30 years ago, Joy Crisp's paper is still considered a decent piece of work worth citing. [1]: http://www.sciencedirect.com/science/article/pii/0377027384900398 [2]: //www.hoelymoley.com/a/631/105 [3]: http://earthquake.usgs.gov/learn/topics/increase_in_earthquakes.php