Surtsey and Mount St. Helens: a comparison of early succession rates

Surtsey and Mount St. Helens are celebrated but very different volcanoes. Permanent plots allow for comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors, and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, we found several common themes. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Surtsey and Mount St. Helens: a comparison of early succession rates

Surtsey and Mount St. Helens are celebrated, but very different volcanoes. Permanent plots allow comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, common themes were revealed. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Aiyansh lava flow, British Columbia

The Aiyansh alkali basalt lava flow is one of the youngest volcanic features of British Columbia, about 220 years old. It issued from a vent area (55° 7′ N, 128° 54′ W) in a narrow tributary valley of the Tseax River, flowed 14 miles (22.5 km) to the Nass Valley, and there spread out in a lava plain 6 miles (9.7 km) long, forcing the river to the northern margin of the valley. The Aiyansh flow has an area of about 15 miles2 (38.8 km2) and a volume of about 0.1 mile3 (0.455 km3).The lava flow is a single cooling unit. Its surface consists of pahoehoe, slab, and block lava in a pattern related to slope, with low slopes favoring preservation of level pahoehoe. Piping and collapse were important about the margins of the lava plain. The eruption must have terminated with a series of lava fountains and explosions in the vent area which built one main and several small cones of bombs and cinders.The Aiyansh flow is entirely a fresh black alkali basalt varying only slightly in crystallinity and texture. Holocrystalline specimens from the interior of the lava plain consist of about 50% plagioclase (An55±5), 10% olivine (Fa35), 30% pyroxene, and 10% opaques. A new chemical analysis confirms that it is a high-iron, low-magnesium, alkali basalt.