Date of Award
Doctor of Philosophy (PhD)
Physical Sciences and Mathematics
Basaltic pāhoehoe lava flows are prevalent throughout the terrestrial bodies of the solar system. This style of volcanism represents both a predominant resurfacing mechanism of planets and natural satellites and a natural hazard to populations living within volcanically active regions on Earth. Pāhoehoe lava flows are also thought to be integral components of flood basalt provinces, which are the largest known lava accumulations by volume and are suggested to be responsible for several mass extinction events throughout Earth’s history. Thus, understanding the dynamics of basaltic lava flows has wide-ranging implications across many fields of geology.
The body of research surrounding the dynamics and rheology of basaltic lava flows spans many orders of magnitude in scale of focus. Large-scale studies of natural lava flows rely on remote sensing techniques to collect data and draw conclusions on behavioral or mechanical phenomena across entire flow fields (tens of kilometers). On the other side of the spectrum, studies of the fine-scale behavior of lava have also augmented our understanding of basaltic flow properties from the perspective of sub-centimeter melt experiments. There remains a substantial gap, however, between these two end-members; studies of basaltic lava flows at the meter-scale are nearly non-existent in comparison. This gap is especially noticeable for pāhoehoe lava flows, which are known to advance and evolve as a function of complex mechanical interactions at the mesoscale (decimeters to meters).
The studies presented here bridge this gap with new research focusing on the emplacement mechanisms, behavior, and rheology of meter-scale pāhoehoe lava flows generated at the world’s first lava flow laboratory, the Syracuse University Lava Project (http://lavaproject.syr.edu). This laboratory is equipped with a high-volume gas-fired tilt furnace capable of melting batches of basaltic rock to super liquidus temperatures (> 1300° C). The resultant melts form glassy pāhoehoe lava flows which are of similar volumetric scale to natural pāhoehoe lava lobes. Like natural lava, a variety of morphologies can be generated such as sheet flows, lobate flows, and channelized flows. The proximity and safety of the laboratory environment allows for direct observation and measurement of critical emplacement parameters such as velocity, thickness, temperature, and rates of effusion. Producing and analyzing data such as these on actively flowing lava has permitted unprecedented research into the rheology and behavior of pāhoehoe lava flows.
One of the themes of the research presented here is understanding the complex relationships between the morphology of a lava flow (the shape of its outer surface) in the context of its inherent physical properties, such as chemical composition and rheology. Models that relate morphology to fluid properties are of critical importance to research in natural lava flows. Often times, especially in the case of planetary geology, the only evidence of active flow conditions is the finite morphology of a flow. Thus, all inferred properties of such lava flows are commonly based solely on morphologic observations. Many studies have addressed the complexities of lava morphology with analyses of cooled lava flows, wax analog flows (polyethylene glycol), and numerical simulations. Experimental lava research, however, allows for the observation of lava morphologies as they form in real-time and correlating those morphologies to direct quantitative measurements.
The first chapter of this dissertation focuses on the relationship between finite morphology and lava flow composition. One of the most recognizable morphologies of basaltic lava flows is known as ropy pāhoehoe. The texture associated with ropy pāhoehoe comprises arcuate, repetitive fold patterns expressed at a variety of scales across a lava surface. Folding of a lava flow surface involves buckling of the viscoelastic crust layer into parallel fold trains and subsequent along-axis stretching of resultant folds. These fold trains typically comprise pairings of antiforms and pinched synforms with axial planes normal to the flow direction. The wavelength and amplitudes of these features is on the order of 1 – 2 cm. This pattern of strain is not restricted to ropy pāhoehoe and can be seen across the compositional spectrum of lavas. Other types of gravity flows, such as glaciers and nappes, also express similar strain patterns. In lava flows, the geometry of folds along a lava crust, specifically fold wavelengths, contains information about the rheology and composition of the flow. The study presented in chapter one includes analyses of fold wavelengths along basaltic lava flow surfaces and incremental strain analysis of experimental lava flows. The results show that a relationship exists between lava flow composition and fold wavelengths, regardless of complex strain history. Thus, using only morphologic observations, lava flow composition can be approximated for folded lavas. This correlation will be of value to fields such as planetary and seafloor geology, where remote observations are commonly used to characterize lava flows.
The second chapter of this dissertation focuses on the rheology of experimental lava flows. More specifically, the viscosity of lava during active flow. Viscosity is a physical property dependent on composition, temperature, and entrainment of flow particles such as bubbles and crystals. All of these properties are constantly changing throughout a flow, thus, as a lava flow evolves, viscosity can change by orders of magnitude through space and time. Therefore, it is one of the most challenging parameters to constrain. Because of this, it has become common practice in volcanology to reduce viscosity to a single value or range, averaging an immense field of complexities. Addressing this problem in the laboratory reduces the inherent challenges associated with traditional volcanologic field work. Presented in chapter two are the first high-resolution spatial and temporal analyses of viscosity for an active lava flow. This revealed the complex evolution of rheology for a lava flow through time with a spatial resolution of 1 cm2. Also revealed in this study is the rheological framework for a transition between sheet flow and channelized flow behavior. This has implications for better understanding channels as a lava transport mechanism.
The third and final chapter of this dissertation focuses on the behavior of lava lobes, the building blocks of pāhoehoe flow fields. Although lobe evolution is critical for the emplacement of pāhoehoe lavas, relatively few studies have addressed mechanisms related to lobe emplacement. Chapter three focuses specifically on lobes exhibiting a sequence of behaviors known as inflation and breakout. Lava inflation involves the overall thickening of a lobe, by either core pressure changes or crustal accretion. Breakouts occur when internal pressures exceed the yield strength of a lava crust, leading to the development of a subsequent lobe. To better understand this process, seven experimental lava lobes were analyzed, revealing high-resolution morphologic and thermal evolution of lobes during inflation and breakout phases. These analyses revealed a consistent pattern wherein the morphologic and thermal properties seem to predict the location of a lava breakout. More specifically, areas of high internal fluid pressure (revealed through thickness analysis) and/or zones of weak exterior crust (revealed through surface temperature analysis) coincide with locations of new lava breakouts. Thus, given sufficient observations of lava thickness and surface temperature patterns during lobe inflation, the location of lava breakouts are predictable. However, the development of these patterns, specifically thermal anomalies representing weak zones of crust, is complex. The results showed that although breakouts are predictable, the series of events leading to breakout represent a complex balance between deterministic and stochastic parameters. These observations may help inform future numerical models of pāhoehoe flow development.
In parallel to these research contributions, an additional goal was to develop new techniques for analyzing the temporal- and spatial-dependent properties of single- and multi-phase lavas flowing on inclined planes. Because lava flows evolve at rapid rates and at excessive temperatures (≥1000° C), there are significant challenges to measuring active flow properties both in the laboratory and in the field. I have addressed this problem with integrated 3D and 4D multispectral imaging techniques that allow for generating high-resolution morphometric and thermal datasets with low uncertainties (described in detail in chapter two). These datasets have been utilized in this dissertation to calculate inherent fluid properties of lava (e.g. viscosity) but can also be used in an array of subsequent investigations in basaltic lava flow dynamics. Such future work could address questions related to non-Newtonian behavior of lava, effects of bulk compositional changes (e.g. SiO2, K2O + Na2O) on rheology, and additional quantitative analyses of morphology.
Experimental lava research represents a significant advance in the field of volcanology, but there are still challenges to overcome. Laboratory lava flows, although similar in scale to natural pāhoehoe lobes, are comprised of pure glass and lack any measurable crystallinity (with few exceptions). Natural lava flows are rarely crystal-free, thus, direct comparisons to experimental lavas are not yet entirely comprehensive. Additionally, the temperature range of experimental lava is much higher than natural flows, with starting temperatures well above 1200° C. Natural basalts erupt and flow at temperatures close to or below 1100° C, thus critical parameters such as cooling rate and viscosity are inherently different than experimental lavas. Overcoming these challenges in the laboratory would require only small adjustments to the current experimental practice, such as reducing starting temperatures. Future advances in this field will undoubtably lead to the generation of flows closer to natural conditions.
The research presented here focuses on addressing a few specific problems related to the emplacement of experimental pāhoehoe lava flows. But more importantly, this work represents advances in a truly nascent field of study. Only a handful of investigations have been conducted so far using experimental lava technology, but the potential and community interest for such research directions is steadily growing. The 2018 eruption of Kilauea marked the end of a 35-year period of daily active lava flows in Hawaii; a significant loss for the volcanological community who relied on this region as a natural laboratory for studies of lava flow dynamics. Because of this, the need for large-scale experimental lava flows will continue to increase in the coming years and, hopefully, the research presented here will serve as a guide for those seeking to advance this field.
Farrell, James, "Viscoelastic Strain, Viscous Rheology, and Behavior of Experimental Lava Flows" (2019). Dissertations - ALL. 1000.