Exceptional coastal exposures of Miocene lava sequences on Banks Peninsula, New Zealand provide an opportunity to understand the emplacement processes of over-thickened lava flows. Field observations of three geochemically variable (nephelinite, hawaiite, and mugearite) over-thickened flows reveal 2-4 m-thick lavas inland that transition into ~50 m cliff-forming compound units toward the ocean. These cliff sections are the result of rapid emplacement of multiple flows that enable cooling as a single unit. Possible eruption rates and reconstruction of various emplacement mechanisms can determine controls on the over-thickening of the aforementioned lava examples. Flow compositions modeled against temperatures and viscosities indicate that viscosities and compositions did not exert a significant influence on the over-thickened morphologies. There is no correlation between geochemistry (especially wt. %SiO2) and the morphology of the overthickened flows, and the close relationship of viscosity to geochemistry suggests that viscosity is not a major factor in the emplacement of these overthickened flows. Computational analysis of viscosities, coupled with measurements of flow dimensions and crystal content, reveal that high effusion rates may have been a critical factor in forming these overthickened flows, with rates of between 400 and 2000 m3 s-1 being likely. Production of more precise ranges of possible rates is hindered by uncertainties associated with taking dimensional measurements of flows as old, weathered, and poorly exposed as these. Additionally, a particularly large margin of error for flow temperatures prevents the drawing of any reasonably precise conclusions with regard to effusion rates. This example illustrates the problems inherent in attempting to quantify such precise numerical parameters for ancient lava flow units. It is very likely that paleo-topography was a very influential factor on these flows’ unique morphologies. Further work should focus on significantly narrowing the margins of error for flow dimensions (thickness and width) and flow temperatures.