Typical Morphology Of Lava Tunnel And Formation Mechanisms

Lava tubes provide an efficient model of lava transportation from the vent to the f-ront in lava flows.Lava tunnels are the traces of lava transportation in basaltic lava flow and play an important role in the nature of lava emplacement.We made a classification of lava tube features on the basis of field observation and discussed their formation, as well as the temperature distribution and velocity gradient of lava tube observed in Laoguipo lava tube and evidence of lava plugs in Dayingshan volcano, in Tengchong volcanic areain this paper. We obtain a Bingham model to ex-plain the mechanism oflava tube, and propose the major effect factor of the formation of circular layer joints is velocity gradient. And then in contrast with the morphology of lava tunnel, a convergence-disperse mechanism of lava tube formation was propo-sed, and thefour steps of formation of Jingfudong lava tunnel was summarized. This oaper supplies a new succession of ignimbrite-forming eruption in Tianchi volcano by testing14C ages of carbonized wood in pyroclastic flow in Silidong lava tunnel. We propose a pulsation and layered mechanism of pyroclastic flow flooding into lava tu-nnel by analyzing the features of ignimbrite and morphology of lava tunnel. And then we discuss some characteristics of vaporization by meeting with water when pyrocla-stic flows flood into lava tunnel. We further propose a cycle of fumarole and rootless vent when pyroclastic flow emplacement controlled by the change of width and dire-ction of lava tunnel.It need more field evidence and simulation experiment to learn how lava plugs in-herit from lava tubes. And there will be some further works in the investigations of Silidong lava tunnel and the pyroclastic flow in it.