火山是怎样形成的
2014-03-05 00:00:00
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<span style="line-height:2;font-family:SimSun;font-size:14px;">在地表以下200公里的温度大约为1500℃，这里的岩石处于高温</span><span style="line-height:2;font-family:SimSun;font-size:14px;">状态，部分熔融形成液态岩浆。由于岩浆的温度比周围的岩石高，</span><span style="line-height:2;font-family:SimSun;font-size:14px;">密度也较小，所以它会向地表上涌，而且在上升过程中还要熔化部</span><span style="line-height:2;font-family:SimSun;font-size:14px;">分周围的岩石。一旦有通达地表的</span><span style="line-height:2;font-family:SimSun;font-size:14px;">通道，它就会立刻喷出地表，形成熔</span><span style="line-height:2;font-family:SimSun;font-size:14px;">岩。火山爆发的熔岩大都来自地下</span><span style="line-height:2;font-family:SimSun;font-size:14px;">100~300公里的地方。</span>
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<img width="600" height="408" alt="" src="/public/html_images/20140305/20140305231354_275.png" />
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<span style="line-height:2;font-family:SimSun;font-size:14px;">火山剖面结构示意图</span>
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<span style="line-height:2;font-family:SimSun;font-size:14px;"><img width="178" height="377" align="left" alt="" src="/public/html_images/20140305/20140305231519_385.png" /><span id="__kindeditor_bookmark_end_50__"></span></span>
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<span style="line-height:2;font-family:SimSun;font-size:14px;">由于大量火山碎屑的喷发溅落</span><span style="line-height:2;font-family:SimSun;font-size:14px;">及火山熔岩的溢出，往往在火山喷</span><span style="line-height:2;font-family:SimSun;font-size:14px;">出口周围形成丘状隆起或者形成中间</span><span style="line-height:2;font-family:SimSun;font-size:14px;">低洼的山。这种隆起或特殊的山就是</span><span style="line-height:2;font-family:SimSun;font-size:14px;">火山锥。当火山喷发作用结束之后，</span><span style="line-height:2;font-family:SimSun;font-size:14px;">由于温度降低，火山口及其周围的岩</span><span style="line-height:2;font-family:SimSun;font-size:14px;">石强烈收缩，从而产生总体沉降，形</span><span style="line-height:2;font-family:SimSun;font-size:14px;">成了低洼的火山口。如果与地下水</span><span style="line-height:2;font-family:SimSun;font-size:14px;">相通，则可以形成湖泊，即形成“天</span><span style="line-height:2;font-family:SimSun;font-size:14px;">池”或“地池”。</span>
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<span style="line-height:2;font-family:SimSun;font-size:14px;"> 火</span><span style="line-height:2;font-family:SimSun;font-size:14px;">山的形成过程</span>
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