The pit-craters and pit-crater-filling lavas of Masaya volcano
The pit-craters and pit-crater-filling lavas of Masaya volcano
复制标题
马萨亚火山的坑洞和填满坑洞的熔岩
DOI：
--
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
A. Harris
中科院分区：
文献类型：
--
作者：
A. Harris
流入坑洞的熔岩会被困住，形成一个不活跃的熔岩湖。在尼加拉瓜马萨亚火山，宁迪里、圣地亚哥和圣佩德罗坑的墙壁上暴露着充满熔岩的岩浆。对这些熔岩的填图表明，充填可以包括‘a’a‘a和pahoehoe两者的侵位，单个充填单元的厚度从2到22微米不等。在高渗漏率时期，具有柱状节理的厚单元被侵位为简单的不活动熔岩湖。较薄的单元序列，可以形成坑底屏障或复合湖泊，以较低的渗漏率就位。熔岩退出导致三个20米厚的单元的无支撑部分下沉，导致单元弯曲和断层，粘性剥离特征表明，至少有一个单元仍处于部分熔融状态时发生了下沉。在没有发生回撤的地方，充填顺序是平躺的，对称地分布在喂料器结构(炉渣锥和堤坝)周围。充满的宁迪里坑以215米厚的层序容纳了5 × 107亿立方米的熔岩。圣地亚哥矿坑部分充填1 × 107m~3的熔岩，填满了110m厚的熔岩序列，其中∼50%被次生矿坑的形成所消耗。在1525-1965年间，总共有6.4 × 107亿立方米的熔岩喷发到宁迪里和圣地亚哥，其中94%的体积保持在坑内；其余的形成了北侧的熔岩流场。坑的发展和填充是一个动态和短暂的过程，对火山形态有短暂的影响，坑的发展和填充需要几个小时到几个世纪的时间。然而，凹坑在塑造一座大厦方面扮演着重要的角色，代表着熔岩汇，并控制熔岩是否被困住或能够扩散到侧翼。
Lava flowing into a pit crater will become entrapped to form an inactive lava lake. At Masaya volcano (Nicaragua) pit filling lavas are exposed in the walls of Nindiri, Santiago and San Pedro pits. Mapping of these lavas shows that fill can involve emplacement of both ’a’a and pahoehoe, with single fill units ranging in thickness from 2 to 22 m. Thick units with columnar joints were emplaced as simple inactive lava lakes during high effusion rate episodes. Sequences of thinner units, which can form pit floor shields or compound lakes, were emplaced at lower effusion rates. Lava withdrawal caused unsupported sections of three 20-m-thick units to subside, resulting in unit flexure and faulting, and viscous peeling features reveal that subsidence occurred while at least one unit was still partially molten. Where withdrawal has not occurred, fill sequences are flat lying and symmetrically distributed around the feeder structures (cinder cones and dykes). The filled Nindiri pit holds 5 × 107 m3 of lava in a 215-m-thick sequence. Partial fill of Santiago pit with 1 × 107 m3 of lava has filled the pit with a 110-m-thick lava sequence, of which ∼50% has been consumed by formation of a secondary pit. Altogether, 6.4 × 107 m3 of lava was erupted into Nindiri and Santiago during 1525–1965, with 94% of this volume remaining pit-contained; the remainder forms a north flank lava flow field. Pit development and filling is a dynamic and ephemeral process, having short-lived effects on volcano morphology, where pits develop and fill over hours-to-centuries. However, pits play an important role in shaping an edifice, representing lava sinks and controlling whether lavas are trapped or able to spread onto the flanks.