Research About lahars

Posted On: Filed Under: Biological Research

Development of vegetation on barren and high elevation sites.

This study is a continuation of work begun in 1980. Current studies include monitoring permanent plots, monitoring grids, studying relict plots, assessing vegetation in potholes, and describing vegetation along transects. The plots studied to date can be divided into those that are fully recovered, those undergoing secondary succession and those undergoing primary succession. The rate of recovery, measured by the number of species and their cover, is related to proximity to sources of colonists and to habitat stress. The species composition of sites undergoing primary succession is related to proximity to intact vegetation and is strongly affected by distance and by chance effects. Previous studies have demonstrated that environmental factors only weakly predict species composition.

 

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Cave biology in the Mount St. Helens Cave Basalt lava flow

This study seeks to establish an inventory of species inhabiting and using lava tubes and caves in the Cave Basalt lava flow. Bat populations in caves are dominated by Plecotus townsendii. Of small mammal species inhabiting or using caves, deer mice (Peromyscus maniculatus) are most wide spread. Few amphibians were observed; the most significant amphibian finding was a population of Larch Mountain salamander (Plethodon larselli). 256 invertebrate species of which approximately 100 species are arthropods have been collected in caves.

 

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Natural establishment of conifers at Mount St. Helens

This study tracks the establishment, survivorship, and growth rate of colonizing conifers on substrates deposited during the 1980 eruption of Mount St. Helens. Two 50 x 50 meter plots were installed at sites on the pyroclastic flow north of the crater and the upper portion of the Muddy River mudflow during 1989 and 1990. Two 50 x 50 meter plots were installed on the debris avalanche in 1993 and 1994. In each plot all individual trees are identified to species, measured (total height and stem diameter at ground level), and tagged.

 

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Summer bird populations of upper subalpine zone of Mount St. Helens, Mount Adams, and Mount Rainier.

Species composition and abundance of summer birds in the upper subalpine zone of Mount St. Helens were compared to those of Mount Adams and Mount Rainier in order to document these populations as well as to examine effects of the May 1980 eruption on bird populations at the volcano.

 

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Surface modification of Muddy River lahar deposit, Mount St. Helens National Volcanic Monument, Skamania County, Washington

Purpose of the project is to note and describe the extent of modification, since 1980, of the surface of the upper Muddy River lahar deposit. Several traverses will involve measurements concerning the density, width, and depth of drainage channels, and changes to interfluve areas. These will be compared with features recorded on aerial photographs and related to longitudinal gradients of channels and surface. The information is to be summarized in a written report.

 

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Effects of eruptions and post-eruptive phenomena on caves and pseudokarst of Mount St. Helens

Beginning June 1980 systematic observations and measurements are documenting the effects of the eruption and post-eruptive events on the caves and pseudokarst of Mount St. Helens. Caves of the Cave Basalt Lava Flow were essentially free of physical impacts by the eruptions, but the biota of some was severely impacted by ashfall. Depending on the local physical geography, some of the caves were severely impacted by post-eruption mudflows.

 

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Long-term succession in subalpine habitats

A long-term study of recovery and primary plant succession in higher elevations was initiated in 1980. The objectives included to document recovery and invasion in several distinct habitats (e.g. lahars, pumice, blasted ridges, tephra) and to determine the mechanisms of invasion and establishment. In addition, large grids of contiguous 100 m2 quadrats have been established since 1986 in several habitats.
Recovery patterns vary with the size and intensity of the initial impacts. Tephra impacted sites were completely recovered by 1983 and subsequent vegetation change has not been directional. In contrast, intensively impacted sites have recovered much more slowly. Recovery rates differ primarily with the degree of isolation, but the intensity of the impact also governs the recovery rate. For example, lahars surrounded by intact vegetation have acquired as many species as intact vegetation, but community structure remains very different. Total cover after 11 growing seasons remains less than 10% of intact vegetation. Nutrients limit the development of biomass and cover, but most species in the immediate vicinity have established on lahars.

 

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Distribution of plant detritus and recovery of plants in deposits of May, 1980 eruption of Mount St. Helens

This study seeks to identify types and sizes of plant material and distance and means of deposition in the May 1980 blast of Mount St. Helens. Types of plant material included pieces of moss, leaves, stems, roots, tree branches and trunks. Four types of transport were identified. The debris avalanche deposited plant material 23 km away. Mudflows (lahars) carried material 75 km to the Columbia River. The pressure blast removed vegetation in a 500 km2 area. Pyroclastic flows in conjunction with the plinian column spread plant debris for at least 75 km in a 110o arc to the north and east. These results are being compared with fossilized records of volcanic eruptions worldwide but especially those from Tertiary western United States.

 

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Climate/microclimate measurements over disturbed sites at Mount St. Helens

Climatic and microclimatic measurements for the summers of 1982 to 1987 were made at three differently disturbed sites around Mount St. Helens. These measurements provided daily information on the physical environment and baseline data for studying the evolution and recolonization of these areas.

 

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Recovery of net primary production in subalpine meadows of Mount St. Helens

Study sites that received tephra or mudflow deposits during the May 1980 eruption were examined and compared for effects on vegetation. Deposition of 5-10 cm of tephra resulted in less species diversity and inhibition of seedling establishment but did not significantly decrease net primary production (NPP); the NPP of these areas did fluctuate dramatically with precipitation rates during seven summers from 1980-1986.

 

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