Bubble bursts in mud: White Island observations and insights from laboratory experiments

• Main Author: Edwards, Matthew John
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury 2015
• Subjects: New Zealand; White Island
• Online Access: http://hdl.handle.net/10092/11768; https://doi.org/10.26021/7389

Phreatic eruptions are common in the recorded history of White Island, New Zealand. Although the larger eruptions have been described in literature, little attention has yet been given to the smaller, more frequent phreatic activity. In addition, the style in which steam bubbles are released during phreatic eruptions at the surface can be highly variable and is poorly understood. Throughout 2013, multiple episodes of phreatic bubble bursts in a mud-sulphur pool occurred at White Island. The first of these episodes, lasting from January 15 to February 7, was well preserved in the video record by GNS staff, tourists and tour operators. Analysis of these videos showed that the mud surface expressions of rising bubbles varied over this period as the apparent high water fraction of the mud pool was first depleted and then regained. Here, these expressions are classified into four regimes, which progressed from 1) low ~8 m, highly fluidal structures to 2) brittle 'starbursting' of hemispheres and heaves of ~40 m height to 3) rapid gas jets followed by high heaves up to ~102 m and finally 4) dry mud venting up to ~67 m height with the complete pool desiccation. Regression back through these regimes from January 30 coincided with the pool returning to the initial fluidal state and a similar depth. Experimental modelling of bubble bursts in mud was conducted in order to identify the influence of viscosity and bubble shape, length and depth on the White Island regimes. An analogue to the White Island mud was created by mixing of kaolinite powder and water to controlled ratios. Bursts were performed at depths of 0.5, 5 and 10 cm in 9 different mud ratios corresponding to an increasing viscosity. Results of these experiments show that viscosity has a negative influence on heave heights but controls the transition from fluidal to brittle structures. Importantly, both a shallowing of bubble depth and an increase to bubble length are shown to increase the height of heaves. Relating experimental results to White Island ...