Establishment of scaling law concerning the intra-conduit mechanics using pumice

通过研制气泡数密度（BND）减压速率仪和微岩屑数密度（MND）出水速率仪，建立了在给定岩浆温度、成分和初始含水量条件下，由BND或MND测量值定量估算减压速率或出水速率的方法。这种方法在自然界的应用揭示了以下几点。对于爆发性喷发，1)普林尼式喷发在气泡成核处的减压速率可达10^6 ~ 10^8 Pa/s，这必须伴随着像稀薄激波那样的快速减压。(2)玄武岩安山岩岩浆次次喷发时，微岩成核处的水溶蚀在不平衡泡化过程中进行扩散限制气泡生长。BND或结晶度与喷发的时间变化有关，如出口速度的变化。3)同时喷发的火山碎屑在估计的出水速率上存在差异，表明管道内的流动是湍流的。对于非爆炸性喷发，4)估计的出水速率约为10^<-5> wt%/s，上升速度为0.01 ~ 0.1 m/s，减压速率为10^2 ~ 10^3 Pa/s。5)在整个导管中，水的析出速率是均匀的。6)尽管目前尚不清楚囊泡是平衡的还是不平衡的，但水的析出可能在导管的较深层进行。这些事实表明，非爆炸性喷发管道中的流动就像塞子流动。通过对囊泡和结晶的联合模拟，并与Couch等（2003）的实验室实验进行对比，我们发现MND是由减压量控制的，通过不平衡囊泡生长的扩散驱动。

Developing bubble number density (BND) decompression rate meter and microlite number density (MND) water exsolution rate meter, we have established the method to quantitatively estimate the decompression rate or water exsolution rate from measured values of BND or MND for given the magma temperature, compositions, and initial water content.Applications of this method to nature have revealed the following things. For explosive eruptions, 1) the decompression rates at bubble nucleation for plinian eruptions are up to 10^6 to 10^8 Pa/s, which must be accompanied by the rapid decompression like due to a rarefaction shock wave. 2) In subplinian eruptions of basaltic andesitic magmas, the water exsolution at the microlite nucleation proceeds the diffusion limited bubble growth during the disequilibrium vesiculation. BND or crystallinity has correlations with the temporal variation of eruptions such as changes of exit velocities. 3)The fact that pyroclasts erupted at the same time have the variation in estimated rates of water exsolution suggests that the flow in the conduit is turbulent For non-explosive eruptions, 4) estimated water exsolution rate is approximately 10^<-5> wt%/s, and 0.01 to 0.1 m/s of ascent velocity and 10^2-10^3 Pa/s of decompression rate. 5)The water exsolution rates are uniform across the conduit 6) The water exsolution might proceeds at deeper level of the conduit though it is still unclear whether the vesiculation is equilibrium or disequilibrium. These facts suggests that the flow in the conduit for non-explosive eruptions is like a plug flow.Carrying out a combined simulation of vesiculation and crystallization, and making a comparison with the laboratory experiments by Couch, et. al. (2003), we have found that MND is controlled by the amount of decompression through the driving force of diffusive bubble growths under disequilibrium vesiculation.