[ENVIRON] Quantifying lava flow dynamics with a very-long-range terrestrial laser scanner

控制熔岩流最大长度的主要因素之一是熔岩的流出速率。有了合理的喷发率估计，现在的模型可以相对准确地预测短期喷发的流量长度。然而，对于较长时间的喷发，最大流动长度还受到复杂过程的控制，如通道爆发的形成、流动膨胀和熔岩管的发展，这仍然是模型的重大挑战。对活动流的观测表明，在相对较短的时间尺度上（以小时为数量级），溢流率的变化可能会通过加强沟道堤岸（从而促进熔岩管形成的可能性）或通过形成突围和驱动沟道切换来强烈影响最大流量长度。因此，为了改进流动模型，了解通量的短期变化对熔岩通道的影响是至关重要的：与目前的模型估计相比，熔岩涌出的涌流通常有助于还是阻碍熔岩管的形成，从而延长或缩短流动长度？解决这些问题的最佳方法之一是获取活动流体的重复地形测量和温度数据，以约束短期积液速率变化所涉及的动力学。现在，超长距离地面激光扫描仪（TLSs）能够对距离达3.5公里的火山地形进行成像，并能提供所需精度的地形数据。然而，在火山上，通常粗糙和不适宜居住的地形会使仪器选址变得耗时和困难，以获得最佳的数据覆盖。此外，测量距离和获取速率之间的权衡意味着在这些距离上，点云数据只能以相对较低的速率获取。因此，对大范围区域的详细调查可能会很慢，这目前阻碍了足够频繁地采集数据以确定流动动力学。这个项目将使用一个非常远程的TLS来调查西西里岛埃特纳火山的活跃熔岩流过程。通过开发测量规划软件工具来优化数据采集程序，可以充分减少测量时间，以便捕获流动动力学。调查规划工具将能够确定最佳仪器位置，并计算自动数据采集程序。地形数据将与地面热成像相结合，以量化涉及通道切换、流量膨胀和裂缝形成的关键过程，这些过程控制了长期熔岩喷发的最终流动长度。TLS调查计划的发展将使在埃特纳火山上持续一天的活动熔岩流的亚小时数据集收集成为可能，那里每年都会发生合适的熔岩流喷发。这些数据将捕捉到喷口和通道区域的地形变化，这些变化表征了渗出率的变化。水流锋面的推进速度和厚度将被确定，水流膨胀（可能先于管道形成）和堤坝不稳定（堤坝坍塌和破口形成的前兆）的证据将与河道通量相关。对于爆发事件，将确定主要通道、流锋和熔岩通量条件，并用于确定不稳定条件。因此，可以考虑爆发充分发展为信道切换事件的要求。

One of the main controls on the maximum length of lava flows is the lava effusion rate. With reasonable effusion rate estimates, models can now forecast the flow lengths for short lived eruptions relatively accurately. However, for longer eruptions, maximum flow lengths are additionally controlled by complex processes such as the formation of breakouts from channels, flow inflation and the development of lava tubes, which remain significant challenges to model. Observations of active flows have revealed that effusion rate variations over relatively short timescales (of order hourly) could strongly influence maximum flow lengths by either reinforcing channel levees (and thus promoting the potential for lava tube formation) or by forming breakouts and driving channel switching. Hence, in order to improve flow models, it is critical to understand the effect of short-term variations in flux on lava channels: do surges in lava effusion generally aid or hinder the formation of lava tubes and hence extend or reduce flow lengths compared to current model estimates? One of the best ways to address these issues is to acquire repeated topographic measurements and temperature data of active flows in order to constrain the dynamics involved during short term effusion rate changes. Very-long-range terrestrial laser scanners (TLSs) are now capable of imaging volcanic terrain over distances up to ~3.5 km, and can deliver topographic data at the accuracy required. However, on volcanoes, the usually rough and inhospitable terrain can make instrument site selection for optimum data coverage time consuming and difficult. Furthermore, a trade off between measurement range and acquisition rate means that at these distances, point cloud data can only be acquired at relatively low rates. Consequently, detailed surveys over extended areas can be slow and this currently prevents data being taken sufficiently frequently for flow dynamics to be determined. This project will use a very-long-range TLS to investigate active lava flow processes on Mount Etna, Sicily. By optimising data acquisition procedures through the development of a survey planning software tool, survey times will be reduced sufficiently for flow dynamics to be captured. The survey planning tool will enable optimal instrument sites to be identified and automated data acquisition procedures calculated. The topographic data will be combined with ground-based thermal imagery in order to quantify the critical processes involved with channel switching, flow inflation and breakout formation that control final flow lengths in long-term lava eruptions. The development of TLS survey planning will enable sub-hourly data set collection over day-long periods of active lava flows on Etna, where suitable lava flow eruptions have occurred annually. The data would capture the topographic changes in the vent and channel regions that characterise changes in effusion rate. The advance rate and thickness of flow fronts will be determined, and evidence for flow inflation (which may precede tube formation) and levee instability (a precursor for levee collapse and breakout formation) correlated with channel flux. For breakout events, the prevailing channel, flow-front and lava flux conditions, will be ascertained and used to identify conditions of instability. Consequently, the requirements for breakouts to fully develop into channel switching events can be considered.