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Magmatic density and viscosity exert fundamental controls on the eruptibility of magmas. In this study, we investigate the extent to which magmatic physical properties control the eruptibility of magmas from Iceland's Northern Volcanic Zone (NVZ). By studying subaerial flows of known age and volume, we are able to directly relate erupted volumes to magmatic physical properties, a task that has been near-impossible when dealing with submarine samples dredged from mid-ocean ridges. We find a strong correlation between magmatic density and observed erupted volumes on the NVZ. Over 85% of the total volume of erupted material lies close to a density and viscosity minimum that corresponds to the composition of basalts at the arrival of plagioclase on the liquidus. These magmas are buoyant with respect to the Icelandic upper crust. However, a number of small-volume eruptions with densities greater than typical Icelandic upper crust are also found in Iceland's neovolcanic zones. We use a simple numerical model to demonstrate that the eruption of magmas with higher densities and viscosities is facilitated by the generation of overpressure in magma chambers in the lower crust and uppermost mantle. This conclusion is in agreement with petrological constraints on the depths of crystallization under Iceland.

岩浆密度与黏度是控制岩浆喷发能力的核心因素。本研究针对冰岛北部火山带（Northern Volcanic Zone, NVZ）的岩浆，探究其物理性质对喷发能力的影响程度。研究通过分析已知年代与体积的陆上熔岩流，得以直接建立喷发体积与岩浆物理性质的关联——而针对洋中脊拖网采集的海底样品开展此类研究几乎难以实现。研究发现，NVZ内岩浆密度与实测喷发体积之间存在显著相关性。总喷发物质体积的85%以上均集中于密度与黏度的最低值区间，该区间对应斜长石（plagioclase）抵达液相线（liquidus）时的玄武岩成分。此类岩浆相对于冰岛上地壳具备浮力。但在冰岛新火山带中，同样存在一批密度高于典型冰岛上地壳的小体积喷发事件。本研究借助简易数值模型证实：密度与黏度更高的岩浆得以喷发，是得益于下地壳与最上部地幔内的岩浆房（magma chamber）产生了超压。该结论与冰岛下方结晶深度的岩石学约束结果一致。