Lahars Research Articles

Forest development following mudflow deposition, Mount St. Helens, Washington

Volcanic mudflows are locally important disturbance agents in the Pacific Northwest rarely studied within the context of forest succession. We describe 18 years (1981–1999) of forest development on the Muddy River mudflow deposit following the 1980 eruption of Mount St. Helens using permanent plot data collected along two transects traversing the Cedar Flats river terrace. We analyze changing forest structure over the study period and compare results with mudflow deposition using correlation and pairwise comparisons, as well as ordination (detrended correspondence analysis) and cluster analysis. Our results show a statistically significant relationship between mudflow deposition and forest change. Following mudflow deposition, the site consisted of patches of high tree mortality caused by deep mudflow deposits in abandoned river channels as well as patches of accelerated regeneration of surviving understory trees in areas of more shallow mudflow deposition and partial overstory mortality. Mudflow deposition at the site initiated multiple stages of stand development with (1) early-colonizing red alder (Alnus rubra Bong.) dominating deep deposition sites with fewer surviving trees, (2) gap recruitment and establishment by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) on intermediate to deep deposition sites with more postburial surviving trees, and (3) late-seral conditions and accelerated succession on shallow burial sites, where tree mortality was low. The initiation of differing succession trajectories, as well as variability in the extent and timing of tree mortality following mudflow deposition, demonstrates a dynamic response to disturbance in relation to small-scale gradients of mudflow deposition.

Calculation of lahar transit times using digital elevation data

Volcanic debris flows, or lahars, represent a significant hazard because of their rapid emplacement, long runout distances, and tremendous destructive potential. Accurate knowledge of advance rates and flow depths is therefore critical to hazard mitigation in lahar-prone areas. With the increasing availability of digital topographic data, models of lahar transit can now be applied to better representative descriptions of natural topography, with the expectation of improved hazard predictions. Using an elementary model of lahar transport dynamics, we have developed a mathematical treatment of lahar propagation over digital topography. Our results show that flow depths and transit times depend on the cumulative effects of changes in local slope along the flow path. These cumulative effects can be significant in predicting lahar advance rates and transit times. In adapting the continuum model to digital topography, we treat the changes in elevation between each adjacent pair of elevations as contiguous inclined planes and establish new boundary conditions sequentially for all downstream intervals to satisfy both local and total volume conservation requirements. Thus, we are able to derive transit times and the evolution of flow velocity and depth profile as a function of distance, x, and time, t. To illustrate the usefulness of this approach, we have applied the model using parameters typical of large volume (10 6 to 10 7 m 3), long runout (25–50 km) lahars at Mt. Ruapehu, New Zealand. By discretizing an analog topography model into N equal-sized intervals, we demonstrate that as N increases, the predicted transit time over the digital topography decreases asymptotically. Several hundred intervals are required to achieve convergence, thus yielding estimates of the minimum resolution of the digital topography (∼10 m vertical, ∼250 m horizontal) required to give accurate transit-time assessments. We also show that one cannot simply model irregular topography as a drop in elevation over a runout distance without risking significant errors in transit-time predications. The result that transit-time predictions decrease with increasing topographic resolution has significant implications for both hazard assessment and the ability to provide timely warnings to communities in the flow paths of lahars.

Changes in vernal pool edaphic settings through mitigation at the project and landscape scale

Vernal pool mitigation is a highly controversial process that has been frequently criticized for its inability to adequately replicate the ecosystem functions of the original intact wetlands. We analyzed past mitigation practices in two rapidly growing counties in California's Great Central Valley to determine if mitigation procedures are re-arranging the vernal pool landscape by substituting more common or less ecologically significant pool types (as defined by soil type and geomorphology) for rarer or ecologically richer pool types. Results indicate that most development projects impacting vernal pools conduct at least a portion of their mitigation requirements at a site with similar edaphic settings. However, when examined at a landscape-scale across all development projects, the more common edaphic settings such as Northern Hardpan and Low Terrace pools are increasing while more rare types such as Northern Claypan and Volcanic Mudflow pools are decreasing. Results also show that Drainageway pools, a less-specialized pool type with generally lower species richness, are becoming more common through mitigation. These results are confirmed by an analysis of landscape diversity, which showed that overall landscape diversity was lower at mitigation sites than at project sites. Despite these results, the ecological significance of vernal pool mitigation practices remains unclear for several reasons. The lack of maps showing exact locations of vernal pools at project sites make it difficult to precisely determine vernal pool acreage and distribution among edaphic settings. Additionally, more research is needed to determine precise relationships between edaphic settings and species distributions and the effects of mitigation area management practices on species distribution and persistence.

Occurrence of hydrogen-oxidizing Ralstonia species as primary microorganisms in the Mt. Pinatubo volcanic mudflow deposits

Ralstonia eutropha is an aerobic, hydrogen-oxidizing, facultative chemolithotrophic bacterium. Recently, R. eutropha-related bacteria have been found to predominate in the cultural bacterial communities of fresh mudflow deposits from Mt. Pinatubo, the Philippines. In the present study, the R. eutropha-related strains were examined for their chemolithotrophic growth in the presence of H2, O2, amd CO2 (85 :5 :10) and for their phylogenetic relationship with R. eutropha. Eleven of the 12 strains tested grew in the presence of H2, O2, and CO2, although the growth was not as rapid as that of the well-characterized H2-oxidizing strain, R. eutropha H16. To examine the hydrogenase activity, membrane and soluble fractions were prepared from R. eutropha-related strain 1245 and its activity was assayed with methylene blue and NAD as electron acceptors. A significant hydrogenase activity was detected in both membrane and soluble fractions of the cell-free extract. The 16S rDNA analysis of the 12 strains of R. eutropha-related bacteria revealed that they could be classified into two clusters, both of which were clearly separated from the cluster of R. eutropha sensu stricto. The probable ecological niche of H2-oxidizing Ralstonia species in the volcanic mudflow deposits was examined.

The characteristics of 1926 volcanic mudflow at Mount Tokachi, the evidences of eyewitnesses and examination of the deposited materials

The characteristics of 1926 volcanic mudflow at Mount Tokachi, the evidences of eyewitnesses and examination of the deposited materials

Soil formation of new lahar materials derived from Mt. Pinatubo

The early stage of weathering / soil formation processes from new volcanic mudflow (new lahar materials) brought from Mt. Pinatubo was examined. For this purpose, comparative studies on the physical / chemical characteristics of the new lahar materials and soils formed by the deposition of old lahar materials were conducted. Original soils contained less coarse sand, more silt, and clay than the new lahar materials. Increase in the clay content of the original soils reflected the progression of weathering. The occurrence of a higher leaching process of Fe, Ca, and Mg and of a moderate accumulation of organic matter in the original soils was suggested, based on the differences in the soil elemental composition and chemical properties. Values of base saturation and phosphate absorption coefficient (PAC) of the new lahar materials were 388% and 44, while those of all the original soils ranged 15–160% and 55–894, respectively. With the progression of weathering, the PAC value tended to increase gradually while the base saturation value decreased abruptly under the environmental conditions prevailing in the Philippines.

浅間山噴火(1783年)に伴う泥流により埋没した畑遺構土壌の理化学的特徴

浅間山噴火(1783年)に伴う泥流により埋没した畑遺構土壌の理化学的特徴

Quinone profiling of bacterial populations developed in the surface layer of volcanic mudflow deposits from Mt. Pinatubo (the Philippines)

The diversity of bacterial populations developed in the surface layer (0–0.25 m depth) of volcanic mudflow deposits from the Mt. Pinatubo volcano (the Philippines) was investigated using quinone profiling. Samples were collected from sites (named N and S1) that had been hit repeatedly by mudflows during successive rainy seasons after the violent eruption of 1991 and also from sites (F1 and F3) covered by mudflow in 1991 but with no deposition in following years. The total microscopic count ranged from 10 8 g −1 (N and S1 sites) to 3.9×10 9 g −1(site F3). In the N sample only three quinone species were detected, while the quinone profiles of samples from sites S3 and F3 showed higher diversity. Tetrahydrogenated menaquinone with eight isoprenoid units [MK-8 (H 4)] was the predominant quinone species in the sample from site N, while MK-8, MK-8 (H 2), MK-8 (H 4), MK-9 (H 4) and MK-9 (H 8) were found as major quinones in the sample from site F3. Because these MK species are known to be the major respiratory quinones of the Actinobacteria, this bacterial group is expected to predominate in the land with primary vegetation recovery following the impact of the volcanic mudflow.

Remote sensing of the 1998 mudflow at Casita volcano, Nicaragua

A devastating lahar (volcanic mudflow) occurred at Casita volcano (Nicaragua) in 1998, triggered by excessive precipitation associated with Hurricane Mitch. We investigate here the morphology and drainage structure of the flow deposition area, primarily using satellite optical and radar imagery. Because the lahar destroyed several towns and villages, killing over 2500 people, we also assess the utility of images available at the time of the event for disaster management. We find that SPOT multispectral data are most suited to delineate and characterize the flow field, but show limitations for damage assessment, and problems with cloud contamination. ERS Synthetic Aperture Radar (SAR) imagery largely failed to detect the lahar deposits, with RADARSAT performing slightly better. The relatively coarse-grained deposits, together with a dense cover of wooden debris, made the flow nearly imperceptible to the short wavelength C-Band radar, especially at ERS's steep incident angle. Because of spatial, spectral and radiometric limitations in all types of imagery used, the synergistic potential of optical and radar, as well as high- and low-resolution optical data was explored. The best synergy was found not in merged imagery, but in the incorporation of auxiliary information, such as elevation, map and GIS data. Given the cloud problem, forthcoming radar satellites with variable polarization and incident angles are expected to provide better results in comparable, future situations.

Satellite remote sensing as a tool in Lahar disaster management.

At least 40,000 deaths have been attributed to historic lahars (volcanic mudflows). The most recent lahar disaster occurred in 1998 at Casita volcano, Nicaragua, claiming over 2,500 lives. Lahars can cover large areas and be highly destructive, and constitute a challenge for disaster management. With infrastructure affected and access frequently impeded, disaster management can benefit from the synoptic coverage provided by satellite imagery. This potential has been recognisedfor other types of natural disasters, but limitations are also known. Dedicated satellite constellations for disaster response and management have been proposed as one solution. Here we investigate the utility of currently available and forthcoming optical and radar sensors as tools in lahar disaster management. Applied to the Casita case, we find that imagery available at the time could not have significantly improved disaster response. However, forthcoming satellites, especially radar, will improve the situation, reducing the benefit of dedicated constellations.

Facies architecture within a regional glaciolacustrine basin: Copper River, Alaska

This paper defines the principal architectural elements present within the Pleistocene, glaciolacustrine basin-fill of the Copper River Basin in Alaska. The Copper River drains an intermontane basin via a single deeply incised trench through the Chugach Mountains to the Gulf of Alaska. This trench was blocked by ice during the last glacial cycle and a large ice-dammed lake, referred to as Lake Atna, filled much of the Copper Basin. Facies analysis within the basin floor allows a series of associations to be defined consistent with the basinward transport of sediment deposited along calving ice margins and at the basin edge. Basinward transport involves a continuum of gravity driven processes, including slumping, cohesive debris flow, hyperconcentrated/concentrated density flows, and turbidity currents. This basinward transport results in the deposition of a series of subaqueous fans, of which two main types are recognised. (1) Large, stratified, basin floor fans, which extend over at least 5 km and are exposed in the basin centre. These fans are composed of multiple lobes, incised by large mega-channels, giving fan architectures that are dominated by horizontal strata and large, cross-cutting channel-fills. Individual lobes and channel-fills consist of combinations of: diamict derived from iceberg rainout and the ice-marginal release of subglacial sediment; multiple units of fining upward gravels which grade vertically into parallel laminated and rippled fine sands and silts, deposited by a range of density flows and currents derived from the subaqueous discharge of meltwater; and rhythmites grading vertically into diamicts deposited from a range of sediment-density flows re-mobilising sediment deposited by either iceberg rainout or the ice-marginal release of sediment. (2) Small, complex, proximal fans, which extend over less than 2 km, and are exposed in the southern part of the basin. These fans are composed of coalescing and prograding lobes of diamict and gravel deposited both directly by subaqueous meltwater and from sediment-density flows. These lobes are cross-cut by a range of sand and gravel-filled troughs and channels cut by subaqueous outwash, and either overlie or are overlain by horizontal sheets of gravel and diamict deposited from a range of sediment-density flows. The fans are, therefore, characterised by a complex, and laterally variable facies, architecture. Water depth, proglacial topography, stability of meltwater portals and sediment supply may all be important in determining the type of subaqueous fan present at any one location. We suggest that the Copper River basin-fill is dominated by packages of sediment containing multiple subaqueous fans with individual fans separated by units of diamict. Each sediment package is in turn separated from the next by a palaeo-landsurface shaped by interstadial/interglacial fluvial processes and by volcanic debris flows.

Hydraulic characteristics of the volcanic mudflow along the Agatsuma River with the 1783 eruption of Mt. Asama

Hydraulic characteristics of the volcanic mudflow along the Agatsuma River with the 1783 eruption of Mt. Asama

Instrumental lahar monitoring at Merapi Volcano, Central Java, Indonesia

More than 50 volcanic debris flows or lahars were generated around Mt Merapi during the first rainy season following the nuees ardentes of 22 November 1994. The rainfalls that triggered the lahars were analyzed, using such instruments as weather radar and telemetered rain gauges. Lahar dynamics were also monitored, using new non-contact detection instrumentation installed on the slopes of the volcano. These devices include real-time seismic amplitude measurement (RSAM), seismic spectral amplitude measurement (SSAM) and acoustic flow monitoring (AFM) systems. Calibration of the various systems was accomplished by field measurements of flow velocities and discharge, contemporaneously with instrumental monitoring. The 1994–1995 lahars were relatively short events, their duration in the Boyong river commonly ranging between 30 min and 1 h 30 min. The great majority (90%) of the lahars was recognized at Kaliurang village between 13:00 and 17:30 h, due to the predominance of afternoon rainfalls. The observed mean velocity of lahar fronts ranged between 1.1 and 3.4 m/s, whereas the peak velocity of the flows varied from 11 to 15 m/s, under the Gardu Pandang viewpoint location at Kaliurang, to 8–10 m/s at a section 500 m downstream from this site. River slopes vary from 28 to 22 m/km at the two sites. Peak discharges recorded in various events ranged from 33 to 360 m 3/s, with the maximum value of peak discharge 360 m 3/s, on 20 May 1995. To improve the lahar warning system along Boyong river, some instrumental thresholds were proposed: large and potentially hazardous lahars may be detected by RSAM units exceeding 400, SSAM units exceeding 80 on the highest frequency band, or AFM values greater than 1500 mV on the low-gain, broad-band setting.

Colonization of a Volcanic Mudflow by an Upper Montane Coniferous Forest at Lassen Volcanic National Park, California

Colonization of a relatively undisturbed 1915 debris flow by an upper montane coniferous forest was examined in Lassen Volcanic National Park in northern California in 1987. Seventy 100-m2 circular plots were arranged in four transects across the flow and sampled to measure tree densities, heights, basal areas and ages. The composition of the forest changed from a mixture of Abies magnifica, Pinus monticola and P. contorta on steep slopes to a forest dominated by P. contorta on shallow slopes. This pattern is typical for these terrains at the 2000-m elevations of the flow. Age data and historical photographs indicated little successful colonization before the late 1930s and peak colonization rates about 1955. Height growth has generally been slow with most trees being >20-y-old but <2-m tall; however, some individuals, including some recent colonizers, have shown rapid growth. This variation among individuals suggests (1) that the earliest colonizers are not necessarily those which will eventually dominate the forest and (2) that opportunities to invade and occupy the canopy may extend for 30 y after the first successful colonization.

EFFECT OF REDUCING CONDITIONS ON THE WEATHERING OF Fe3+-RICH BIOTITE IN THE NEW LAHAR DEPOSIT FROM MT. PINATUBO, PHILIPPINES

Biotite in the new lahar (volcanic mud flow) deposit from Mt. Pinatubo, Philippines (hereafter referred to as P-Bt) was easily converted to vermiculite during lowland rice-cultivation in pots. The K 2 O content of the P-Bt gradually decreased, and the peak intensity of the X-ray diffraction (XRD) at 1.4 nm increased during seven cultivations of the paddy rice. The amount of K + release from the P-Bt with Na 2 S 2 O 4 treatment was about 1.2 times greater than that released with a NaCl treatment when they were compared at the same pH and Na + concentration. This result was considered to be a characteristics of biotite containing a large amount of Fe 3+ because the amount of K + released from two reference biotites having a Fe 3+ /total Fe ratio of < 0.1 was smaller after the Na 2 S 2 O 4 treatment than after the NaCl treatment. Fe 3+ at the edge site of the P-Bt might react with the reducing agent, and released Fe 2+ and other polyvalent cations might replace the interlayer K + because a 1.4-nm reflection peak appeared after the Na 2 S 2 O 4 treatment. The reducing conditions during lowland rice cultivation could facilitate vermiculitization of the P-Bt and contribute to the K + supply for the rice plants. The characteristics of the P-Bt were confirmed by XRD, infrared absorption (IR) spectroscopy, and elemental analysis. The trioctahedral type was also confirmed from the (060) reflection peak at 0.153 nm. IR bands of P-Bt were observed in the 400-1400-cm -1 and 3400-3700-cm -1 region. The IR bands of P-Bt from 400 to 1400 cm -1 were very similar to those for the two reference biotites whereas the IR bands in the 3400 to 3700 cm -1 region of the P-Bt differed from those for the reference biotites. The atomic Mg/Fe ratio of the P-Bt was 1.56, which was in the range of biotite. The atomic Fe 2+ /total Fe ratio of the P-Bt was 0.47, and its average structural formula was K 0.74 ,Na 0.09 (Si 2.80 ,Al 1.20 )(Al 0.06 ,Fe 3+ 0.50 ,Fe 2+ 0.45 ,Mg 1.48 , Ti 0.21 )O 10 (OH) 2 .

Lahar hazard micro-zonation and risk assessment in Yogyakarta city, Indonesia

Yogyakarta urban area (500,000 inhab.) is located in Central Java on the fluvio-volcanic plain beside Merapi volcano, one of the most active of the world. Since the last eruption of Merapi in November 1994, the Code river, which goes across this city, is particularly threatened by lahars (volcanic debris flows). Until now, no accurate hazard map exists and no risk assessment has been done. Therefore, we drew a detailed hazard map (1/2,000 scale), based on morphometric surveys of the Code channel and on four scenarios of discharge. An additional risk assessment revealed that about 13,000 people live at risk along this river, and that the approximate value of likely loss is US $ 52 millions. However, the risk level varies between the urban suburbs.

Rheological properties of a remobilised‐tephra lahar associated with the 1995 eruptions of Ruapehu volcano, New Zealand

Volcanic activity at Ruapehu during 1995/96 represents the most voluminous volcanic activity in New Zealand this century. Early in the eruption sequence, lahars were generated by the ejection of water, lake sediments, and pyroclastic material from the summit Crater Lake. Lahars (volcanic debris flows) generated by the remobilisation of pyroclastic fall deposits on the upper slopes of the volcano followed the two largest tephra‐producing eruptions in October 1995, representing a previously unrecognised hazard. Prediction and mitigation of such hazards requires quantitative knowledge of initiation processes, lahar mechanics (i.e., rheology), and appropriate hydrodynamic routing for channelised flows. The rheological properties of a remobilised tephra lahar in the Mangatoetoenui valley were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits. Calculated maximum flow velocities of 12–27 m/s, volumetric flow rates of 1300–2000 m3/s, shear strengths of 1.9–3.4 × 103 Pa, and plastic viscosities of 29–93 Pa.s compare well with measured and estimated examples cited in the literature, and may aid in understanding and constraining this new class of hazard at Ruapehu volcano.

Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines

Fire and Mud is a comprehensive document of the awakening of a volcano after a 500-year sleep. Its 62 technical papers tell the scientific and human story of the 1991 eruption of Mount Pinatubo and the events surrounding it.Second in size this century only to an eruption in Katmai, Alaska, in 1912, and ten times larger than the eruption of Mount St. Helens in 1980, Pinatubo's eruption threatened the lives of a million people. A giant ash cloud rose 35 kilometers into the sky and hot blasts seared the countryside, a more serious disaster was averted by timely, accurate warnings. Philippine authorities were able to evacuate 60,000 people from the slopes and valleys, and the American military evacuated 18,000 personnel and their dependents from Clark Air Base below the mountain -- thus saving many thousands of lives and an estimated billion dollars in property and making this the most successful case of volcanic hazards mitigation in history.In this impressive volume, volcanologists and other experts from 10 countries explore the precursors, processes, and products of the eruption, as well as record-setting erosion and lahars (volcanic mudflows) that followed. Nearly half of what the eruption deposited on Pinatubo's slopes has now been eroded and dumped, in repeated rounds of terror, on villages at the foot or the volcano. The eruption also injected so much sulfur dioxide into the stratosphere that the global climate was cooled for about two years.Volcanologists and civil defense officials will consult this book for years to come as they seek to understand large eruptions and to protect communities at risk from long-dormant volcanoes. Scholars and students will find here aninterdisciplinary view of a fascinating, incredibly dynamic geologic system. Others with a modest technical background and interest in volcanoes will find many individual essays of interest.

Hydraulic Model Test on Volcanic Mudflow in Suzawa Area

Hydraulic Model Test on Volcanic Mudflow in Suzawa Area

A Chronological Study of Volcanic Mudflows into the Furano River at Mt. Tokachi

A Chronological Study of Volcanic Mudflows into the Furano River at Mt. Tokachi