Debris Pile Research Articles

High regeneration may not contribute to the forest's carbon storage: a case study in the mangrove forest of Rajang-Belawai-Paloh delta, Sarawak.

The alarming rate of the mangrove ecosystem loss poses a threat of losing valuable carbon sinks. This study was conducted to (i) determine the growth structure in different vegetation types and (ii) compare the aboveground biomass (AGB) and carbon storage in different vegetation types. The study was conducted at four vegetation types within the Rajang-Belawai-Paloh delta i.e., Matured Bakau-Berus Forest (MBBF), Bakau-Nipah Forest (BNF), Regenerating Forests (Debris pile) [RF-D], and Regenerating Forests (Machinery track) [RF-M]. Inventory plots (20 m × 20 m) are systematically located along the main waterways and smaller rivers/streams. Trees (≥ 5 cm diameter-at-breast height [DBH]), seedlings (< 2-cm stem diameter), and saplings (2-4.9-cm stem diameter) were measured. The trend of total trees per hectare is found to be decreasing across the least disturbed vegetation (MBBF) to the most disturbed vegetation (RF-M). The trends of total seedlings and saplings per hectare are found to be going upwards from the least disturbed vegetation to the most disturbed vegetation. Kruskal-Wallis H-test showed that there is a significant difference in the AGB and carbon storage between different vegetation types, χ2(2) = 43.98, p = 0.00 with the highest mean rank AGB and carbon storage in BNF (612.20 t/ha) and lowest in RF-M (287.85 t/ha). It can be concluded that although the most disturbed vegetations have higher regeneration, it may not contribute to the forest's carbon storage The naturally regenerated seedlings may not grow beyond the sapling stage unless sustainable forest management is conducted to ensure survivability and growth.

A 15-year follow-up study of mortality in a pooled cohort of World Trade Center rescue and recovery workers

IntroductionHazardous exposures from the World Trade Center (WTC) terrorist attacks have been linked to increased incidence of adverse health conditions, often associated with increased mortality. We assessed mortality in a pooled cohort of WTC rescue/recovery workers over 15 years of follow-up. Materials and methodsWe analyzed mortality through 2016 in a pooled and deduplicated cohort of WTC rescue/recovery workers from three WTC-exposed cohorts (N = 60,631): the Fire Department of the City of New York (FDNY); the WTC Health Registry (WTCHR); and the General Responder Cohort (GRC). Standardized mortality ratios (SMRs) were estimated to assess mortality vs. the US and NY state populations. Multivariable Cox proportional hazards models were used to examine associations of WTC exposures (date of first arrival, working on the WTC debris pile) with mortality risk. ResultsThere were 1912 deaths over 697,943.33 person-years of follow-up. The SMR for all-cause mortality was significantly lower-than-expected, both when using US (SMR 0.43, 95% confidence interval [CI] 0.42–0.45) and NYS (SMR 0.51, 95% CI 0.49–0.53) as reference populations. SMRs were not elevated for any of the 28 major causes of death. Arriving at the WTC site on 9/11-9/17/2001 vs. 9/18/2001-6/30/2002 was associated with 30–50% higher risk of all-cause, heart disease and smoking-related mortality in non-FDNY/non-GRC members. Conversely, arriving on 9/11/2001 vs. 9/18/2001-6/30/2002 was associated with 40% lower all-cause and smoking-related mortality risk in FDNY members. Working on vs. off the WTC pile was associated with an increased risk of all-cause mortality in non-FDNY/non-GRC members (adjusted hazard ratio [aHR] 1.25, 95% CI 1.04–1.50), and cancer-specific mortality in GRC members (aHR 1.39, 95% CI 1.05–1.84), but lower mortality risks were found in FDNY members. ConclusionsWe did not observe excess mortality among WTC rescue/recovery workers compared with general populations. However, significantly increased mortality risks among some sub-groups with high WTC exposure warrant further investigation.

Pioneer palm tree as an ecosystem engineer: Effects on ant community structure

AbstractEcosystem engineer species can affect the assembly and maintenance of biological communities by altering local environmental conditions. Several palm tree species play this role in changing the surrounding environment mainly through the fall of entire rachis and the formation of a thick and homogeneous leaf litter layer beneath the canopy. However, their impact on soil animal communities remains unclear. In particular, soil organisms (e.g. ants) can be negatively affected by palm‐driven local changes, since they are especially susceptible to leaf litter changes. Our objective was to test if the presence of palm trees reduces alpha and beta diversities of ant communities at taxonomic and morphometric levels. We also tested if palm tree understory mound (debris pile just below the canopy) area and population density reduce ant community alpha and beta diversities (at the taxonomic and morphometric levels) in tropical rainforests. To do so, we described taxonomic and morphometric diversity patterns of ant communities in a relictual landscape of the Atlantic Rainforest (northeastern Brazil) using Hill's numbers approach in two habitats: understory mounds surrounding the palm tree species Acrocomia intumescens, and forest understory without A. intumescens (non‐palm understory). Our main findings were: (1) Taxonomic and morphometric alpha diversity were similar between A. intumescens understory mound and non‐palm understory; (2) Ant communities in non‐palm understory presented higher beta diversity than communities from A. intumescens understory mounds considering both rare species and morphometric traits; (3) A. intumescens understory mound area negatively affected common and dominant ant species; and (4) the interaction between understory mound area and the population density of A. intumescens affected dominant ant species in complex ways and the outcomes depend on the balance between both predictors. Our findings point to an important role of palm trees as ecosystem engineers in reducing ant biodiversity and changing the functional signature of human‐modified tropical rainforests.

Grasping and Transport of Unstructured Collections of Massive Objects

We present a collection of sensorimotor models which, when paired with a custom, mobile manipulation platform, collectively enable the autonomous deconstruction of piles of debris to facilitate mobility in cluttered spaces. The models address the problems of visual debris segmentation, object selection, and visual grasp planning. They also exercise proprioceptive grasp control, and force-controlled object extraction to enact the grasping plan. The object selector segments a debris pile into a set of parts that appear disjoint from one another and executes a rule-based decision program to select the object that appears easiest to extract. Then a grasp planner identifies a grasping point and hand preshape at a location where the gripper configuration fits the shape of the object, while also satisfying kinematic and collision-avoidance constraints. Our geometric grasp-prototype concept allows the planner to establish grasp suitability by fitting a set of shape-grasp primitives to a 2.5D depth image of the pile. The robot then applies the grasp reactively, pushing against the object until a preset resistance is met. Finally, an admittance controller guides object extraction, allowing a prescribed end-effector compliance along task-frame axes to minimize adverse forces and torques on the hand. We show experiments demonstrating the applicability of those models in isolation and in concert, including grasp tests conducted on objects representative of of a human-scale urban environment.

Load-Settlement Behavior of Concrete Debris Pile in Fly Ash Fill

Abstract This study addresses the problem of disposal and effective reuse of waste material, fly ash, and construction concrete debris in order to find an optimized solution for their bulk disposal...

Effects of debris piles and pools along dry riverbeds on nutrients, microbial activity, and ground-dwelling arthropods: A Namibian ephemeral river case

Debris piles and dry pools are common landscape elements along ephemeral river channels. However, their effects on resource availability and arthropod species diversity have been neglected so far. We investigated whether debris piles and pools along dry riverbeds generate nodes of environmental resources, influence microbial activity, and provide key habitats for ground-dwelling arthropods. We studied three different habitats (channel, debris pile and dry pool) to analyze organic matter, nutrients and microbial activity in dry sediments, and included two further habitats (riparian and upland areas) for ground-dwelling arthropod assemblages along a major ephemeral river (Ugab River, NW Namibia). We observed higher concentrations of organic matter and macro- and micro-nutrients in debris piles than in pools, and higher concentrations in both landscape elements than in the sandy channel matrix. Microbial activity showed a positive relationship with organic matter and nutrient availability in sediments. Debris piles, dry pools and channels harbored diverse and abundant ground-dwelling arthropod assemblages similar to adjacent terrestrial areas. Debris piles and pools differed in assemblage composition not only from riparian and upland areas but also from the sandy channel matrix. Overall, debris piles and dry pools acted as nodes of soil fertility, enhanced microbial activity, and shaped ground-dwelling arthropod assemblages.

Pulmonary Fibrosis among World Trade Center Responders: Results from the WTC Health Registry Cohort.

Dust created by the collapse of the World Trade Center (WTC) towers on 9/11 included metals and toxicants that have been linked to an increased risk of pulmonary fibrosis (PF) in the literature. Little has been reported on PF among WTC responders. This report used self-reported physician diagnosis of PF with an unknown sub-type to explore the association between levels of WTC dust exposure and PF. We included 19,300 WTC responders, enrolled in the WTC Health Registry in 2003–2004, who were followed for 11 years from 2004 to 2015. Exposure was defined primarily by intensity and duration of exposure to WTC dust/debris and work on the debris pile. Stratified Cox regression was used to assess the association. We observed 73 self-reported physician-diagnosed PF cases, with a PF incidence rate of 36.7/100,000 person-years. The adjusted hazard ratio (AHR) of PF was higher in those with a medium (AHR = 2.5, 95% CI = 1.1–5.8) and very high level of exposure (AHR = 4.5, 95% CI = 2.0–10.4), compared to those with low exposure. A test for exposure—response trend was statistically significant (Ptrend = 0.004). Future research on WTC dust exposure and PF would benefit from using data from multiple WTC Health Program responder cohorts for increased statistical power and clinically confirmed cases.

Hydrological Barrier as a Cause of Salt Marsh Loss

ABSTRACT Huff, T.P. and Feagin, R.A., 2017. Hydrological barrier as a cause of salt marsh loss. In: Martinez, M.L.; Taramelli, A., and Silva, R. (eds.), Coastal Resilience: Exploring the Many Challenges from Different Viewpoints. Journal of Coastal Research, Special Issue No. 77, pp. 88–96. Coconut Creek (Florida), ISSN 0749-0208. The Magic Ridge Marsh located along Magnolia Beach, Texas has rapidly degraded over the last few decades. This marsh is of great importance to wildlife and dependent recreational pursuits such as bird watching at the Magic Ridge Sanctuary and fishing in the marshes and adjacent bay. In this study, we decided to focus on the shell debris pile as aerial imagery, along with local knowledge, indicated that this was the point of hydrologic disturbance. In order to restore this ecosystem, the alterations to the hydrology had to be understood and thus the multi-stage approach was chosen to single out the environmental factors that influence the marsh. Land cover analyses were conducted...

Disaster debris estimation using high-resolution polarimetric stereo-SAR

This paper addresses the problem of debris estimation which is one of the most important initial challenges in the wake of a disaster like the Great East Japan Earthquake and Tsunami. Reasonable estimates of the debris have to be made available to decision makers as quickly as possible. Current approaches to obtain this information are far from being optimal as they usually rely on manual interpretation of optical imagery. We have developed a novel approach for the estimation of tsunami debris pile heights and volumes for improved emergency response. The method is based on a stereo-synthetic aperture radar (stereo-SAR) approach for very high-resolution polarimetric SAR. An advanced gradient-based optical-flow estimation technique is applied for optimal image coregistration of the low-coherence non-interferometric data resulting from the illumination from opposite directions and in different polarizations. By applying model based decomposition of the coherency matrix, only the odd bounce scattering contributions are used to optimize echo time computation. The method exclusively considers the relative height differences from the top of the piles to their base to achieve a very fine resolution in height estimation. To define the base, a reference point on non-debris-covered ground surface is located adjacent to the debris pile targets by exploiting the polarimetric scattering information. The proposed technique is validated using in situ data of real tsunami debris taken on a temporary debris management site in the tsunami affected area near Sendai city, Japan. The estimated height error is smaller than 0.6m RMSE. The good quality of derived pile heights allows for a voxel-based estimation of debris volumes with a RMSE of 1099m3. Advantages of the proposed method are fast computation time, and robust height and volume estimation of debris piles without the need for pre-event data or auxiliary information like DEM, topographic maps or GCPs.

Abstract 3435: Prostate cancer in WTC respondents

Abstract Background: Ten years following the 9/11/2001 attacks on the World Trade Center (WTC), an increased incidence of prostate cancer was reported in two separate cohorts of WTC rescue and recovery workers. Whether this increase is due to WTC-related exposures or increased surveillance is uncertain. Methods: Prostate cancer cases and Gleason scores diagnosed after 9/11 from 2002 to 2014 were obtained from the WTC Health Program (n = 180). Differences in proportions of Gleason scores 7+ (moderate to high-grade cancer) in WTC respondents and New York State were calculated based on the NYS Cancer Registry (NYSCR). An age-adjusted rate for Gleason scores of ≥7 was calculated using the indirect method based on NYSCR. Age- and race-matched prostate cancer non-WTC respondent controls (n = 253) were obtained from Mount Sinai Hospital. We evaluated the effects of WTC-respondent status, exposure level, age, race, prostate-specific antigen (PSA) concentrations, and clinical stage on Gleason scores using log-linear regression. WTC exposure was analyzed by four categorical levels and continuously using a relative rank of potential carcinogen-related post-9/11 exposures. Differences in mean numbers of PSA screening visits were assessed using Student's t-test. Results: The age-adjusted rate for a Gleason score ≥7 was 1.15 for WTC respondents (95% Confidence Interval (CI): 0.94, 1.36) compared to the NYSCR. WTC respondents &amp;lt; 40 years old had an 8-time higher proportion of aggressive cancers than expected based on NYSCR age-specific rates. The proportion of Gleason scores ≥7 was 0.33 (95% CI: -0.06, 0.12) higher in WTC respondents than NYSCR. WTC respondents had lower Gleason scores (Odds Ratio (OR): 0.90 (95% CI: 0.82, 0.99)), PSA values (OR: 0.79; 95% CI: 0.71, 0.89), but higher clinical stage (OR: 1.04; 95% CI: 0.92, 1.16) than controls. When Gleason score was adjusted for PSA and clinical stage, the OR for PSA testing was 1.04; 95% CI: 0.88, 1.23 and clinical stage was lower (OR: 0.82; 95% CI: 0.69, 0.98) in WTC-respondent cases. The mean numbers of PSA-screening visits were not different between WTC respondents and controls (t = 0.64; P = 0.52) and were not associated with Gleason scores ≥7 (OR: 1.0; 95% CI: 0.88, 1.13). Four-level exposure categories (OR: 0.99; 95% CI: 0.99, 1.00) and continuous rank (OR: 0.88; 95% CI: 0.73, 1.06) showed no associations with Gleason scores. Days spent at WTC (OR: 1.00; 95% CI: 1.00, 1.03) and working on the WTC debris pile (OR: 0.95; 95% CI: 0.86, 1.05) showed similar results. Conclusions: Young WTC respondents had higher Gleason scores than the NYSCR. Number of PSA screening visits did not significantly differ between WTC respondents and controls and PSA values of WTC respondents were lower than controls. Aggressive prostate cancer was not associated with WTC exposure levels. Considering the high grade of prostate cancer in younger men and the long latency for prostate cancer development, continued monitoring is needed to determine alternative causes of elevated prostate cancer in the WTC population. Citation Format: Dana Hashim, Paolo Boffetta, William Oh, Sylvain Wallenstein, Matthew Galsky, Emanuela Taioli. Prostate cancer in WTC respondents. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3435.

The collapse of WTC 7: A re-examination of the “simple analysis” approach

Although the events of that tragic day happened 14 years ago, there remain nagging questions of why the 47 storey WTC 7 steel framed structure collapsed, when it was NOT hit by an airplane. We will review the official rationale of how the collapse events started, and why, in our opinion, the explanation is judged to be wrong. Then, we will proceed with another scenario that says “Okay – let’s assume that the two critical storeys did sustain extremely hot fires, so much so that 2/3rds of their columns totally lost axial resistance capability”. We then proceed to employ Newton’s laws to inquire whether there was sufficient gravitational potential energy due to live and dead loadings in upper and lower floors to overcome the resistance offered by the remaining columns, together with floor slabs known to have been pulverized to reduced particle sizes by surface to surface crushing. Our conclusion suggests that Newton’s laws of motion and energy conservation considerations would have had to have been violated to explain that building’s total collapse within a debris pile several storeys high. Supplementary Sources: Clip from 9-11 in the Academic Community

Static and dynamic analyses of the stability of mining wastes (Ravaneti) in the Carrara marble area (Apuan Alps, Italy) / Analiza statyczna i dynamiczna stabilności hałd odpadów górniczych w regionie wydobycia marmurów Carrara (Alpy Apuańskie, Italia)

Abstract The problem of the stability of “ravanetos” (debris piles of mining waste material extracted from the Apuan Alps, Italy) is very relevant, because of the consequences a landslide would have on the people and the existing civil infrastructures throughout the territory. In this work, the stability of two ravanetos that can be considered as representative of those in the Carrara area has been studied: the Polvaccio ravaneto, a recent type of debris pile and the Torrione-Tecchione, an old debris pile at present undergoing re-naturalisation. The study using the LEM (Limit Equilibrium Method) in a static and pseudo-static field, has made it possible to first carry out a back-analysis to define the most probable apparent cohesion and friction angle values of the material that makes up the ravanetos. Subsequently, it was possible to determine the intensity of the seismic wave that would be able to lead the two ravanetos to limit stability conditions and to determine the probability of such a seismic wave occurring in the next 50 years. A more accurate analysis, carried out with a numerical method in the dynamic field, of the most critical condition (the Polvaccio ravaneto) has led to more conservative results (higher safety factors) than those obtained with the LEM. This result allows us to reveal how the LEM can be considered a cautionary instrument to judge the stability of debris piles during a seismic event and that the likelihood of a landslide occurring in the two studied representative ravanetos over the next 50 years is very slim.

Sarcoidosis Diagnosed After September 11, 2001, Among Adults Exposed to the World Trade Center Disaster

Explore relationships between World Trade Center (WTC) exposures and sarcoidosis. Sarcoidosis has been reported after exposure to the WTC disaster. We ascertained biopsy-proven post-9/11 sarcoidosis among WTC Health Registry enrollees. Cases diagnosed after Registry enrollment were included in a nested case-control study. Controls were matched to cases on age, sex, race or ethnicity, and eligibility group (eg, rescue or recovery worker). We identified 43 cases of post-9/11 sarcoidosis. Twenty-eight incident cases and 109 controls were included in the case-control analysis. Working on the WTC debris pile was associated with sarcoidosis (odds ratio 9.1, 95% confidence interval 1.1 to 74.0), but WTC dust cloud exposure was not (odds ratio 1.0, 95% confidence interval 0.4 to 2.8). Working on the WTC debris pile was associated with an elevated risk of post-9/11 sarcoidosis. Occupationally exposed workers may be at increased risk.

Temperature and gas evolution during large scale outside storage of wood chips

The temperature and gas concentrations in a newly established pine-wood debris pile of 20 m×15 m×6 m in dimensions (approximately 400 tons of fresh weight material) were monitored for 150 days. Temperature was measured at ten different positions within the pile, while concentrations of CO2, O2, CO and CH4 were taken at four different representative locations. The pile was characterized by a strong temperature increase within the first 10–12 days of storage. Results of the gas analysis in this period suggest that the temperature increase was caused by microbial processes. In particular, reduced oxygen concentration and almost complete absence of methane indicate mainly aerobic respiration processes. Effects of weather conditions on the temperature/gas distribution and time evolution are also discussed in the paper.

A microseismic approach to locate survivors trapped under rubble

ABSTRACTThe detection of microseismic noise generated by survivors trapped by debris is a method already used by Search and Rescue (S&amp;R) teams. Present seismic S&amp;R equipment works exclusively on energy analysis whilst ignoring information associated with propagation delays. We explore the potential of using traveltime analysis compared to energy analysis for both 2D and 3D location. Results obtained from three different debris field scenarios used for training S&amp;R teams demonstrate that using travel‐time information is more reliable than using energy information alone. A joint analysis of both signal parameters is suggested as an appropriate strategy to improve the reliability of locating survivors. Traveltimes can also potentially extend the location into the third dimension by returning an approximate estimate of the survivor depth below ground level. The main obstacles to achieving this goal are the inhomogeneity of the debris pile, the need for a real‐time response and the limited spatial extension of the sensor array. Despite these difficulties, results obtained in the field, with an algorithm based on energy focusing by means of cross‐correlation and semblance operators, show an accuracy within the limit of the seismic resolution. A new searching strategy is defined and the procedure reduces the investigation time taken by current seismic S&amp;R systems by a factor of three.

An overview of 9/11 experiences and respiratory and mental health conditions among World Trade Center Health Registry enrollees.

To date, health effects of exposure to the September 11, 2001 disaster in New York City have been studied in specific groups, but no studies have estimated its impact across the different exposed populations. This report provides an overview of the World Trade Center Health Registry (WTCHR) enrollees, their exposures, and their respiratory and mental health outcomes 2–3 years post-9/11. Results are extrapolated to the estimated universe of people eligible to enroll in the WTCHR to determine magnitude of impact. Building occupants, persons on the street or in transit in lower Manhattan on 9/11, local residents, rescue and recovery workers/volunteers, and area school children and staff were interviewed and enrolled in the WTCHR between September 2003 and November 2004. A total of 71,437 people enrolled in the WTCHR, for 17.4% coverage of the estimated eligible exposed population (nearly 410,000); 30% were recruited from lists, and 70% were self-identified. Many reported being in the dust cloud from the collapsing WTC Towers (51%), witnessing traumatic events (70%), or sustaining an injury (13%). After 9/11, 67% of adult enrollees reported new or worsening respiratory symptoms, 3% reported newly diagnosed asthma, 16% screened positive for probable posttraumatic stress disorder (PTSD), and 8% for serious psychological distress (SPD). Newly diagnosed asthma was most common among rescue and recovery workers who worked on the debris pile (4.1%). PTSD was higher among those who reported Hispanic ethnicity (30%), household income <$25,000 (31%), or being injured (35%). Using previously published estimates of the total number of exposed people per WTCHR eligibility criteria, we estimate between 3,800 and 12,600 adults experienced newly diagnosed asthma and 34,600–70,200 adults experienced PTSD following the attacks, suggesting extensive adverse health impacts beyond the immediate deaths and injuries from the acute event.

Chemical characterization of ambient particulate matter near the World Trade Center: Source apportionment using organic and inorganic source markers

Concentrations of alkanes (C20–C35), 14 polycyclic aromatic hydrocarbons (PAHs) and PAH ketones, and three hopanes are reported from four locations near the World Trade Center (WTC) (three of the locations within 300 m of the debris pile). The highest concentrations of individual PAHs across the four locations were for fluoranthene (10.3 ng/m 3 at site W), pyrene (8.7 ng/m 3 at site W), and chrysene (6.2 ng/m 3 at site W). The EPA Unmix Version 6.0 receptor model was used to estimate the impact of WTC fires and recovery efforts on ambient PM 2.5 concentrations. Five factors were identified: open burning of building debris, smoldering fires from building debris, a mixed recovery source, a sulfate/debris removal source, and motor vehicle exhaust.

Twenty-nine months of geomorphic change in upper Monterey Canyon (2002–2005)

Time serial multibeam bathymetry is used to evaluate geomorphic trends and submarine processes in the upper 4 km of Monterey Canyon, California. Seven high-resolution bathymetric surveys conducted between September 2002 to February 2005 show that the upper canyon axis and head grew in volume 1 000 000 m 3 ± 700 000 m 3, at an average annual rate of 400 000 m 3/a ± 300 000 m 3/a through lateral erosion and vertical incision. This net loss of substrate during the 29-month period is parsed between local erosion of 1 400 000 m 3 and local deposition of 350 000 m 3. A submarine landslide with a scar void volume of 70 000 m 3 and debris pile of 52 000 m 3 occurred between March 2003 and September 2004. During the subsequent months until February 2005, the slide scar grew 40% in volume while the debris pile shrank by 80%. The canyon-head rim adjacent to Moss Landing Harbor prograded seaward and retreated shoreward significantly (up to 50 m) during the study suggesting frequent episodes of sediment build up and subsequent down-canyon failure. A large field of sand waves located in the channel axis was completely reworked in each time series except for a 24 h period where no wave crest movement was noted, and a 32 day period where up-canyon migration of approximately 7 m was recorded in the northern tributary.

Kinematics of Sand Avalanches Using Particle-Image Velocimetry

ABSTRACT The avalanching of granular material at slope angles between the angle of repose and the angle of maximum stability, such as on a sandpile or on the lee (slip) face of a sand dune, typically produces droplet-shaped flows that consist of a well-defined head at the front. We have performed the first experiments on granular materials using the particle-image velocimetry (PIV) technique, in which we have studied avalanching flows of sand for different surface properties. Our results suggest that the presence of a deformable bed (layer of loose or erodible particles) on the surface is a necessary condition for the occurrence of these flows. We measured for the first time the surface-velocity field in avalanches propagating at angles between the angle of repose and the maximum angle of stability, and observed a transition in the flow behavior with downstream distance, from a surface-like flow to a compressing flow that has the characteristics of a shock wave propagating through the deformable bed. Measurements for sand avalanches seem to indicate that the features of this transition depend on the inclination angle of the surface in the small range between these two critical angles. The results suggest that grainflow laminae and scoria cone flanks, for example, are formed by flows that in their upper part propagate as a surface flow, and in their lower part propagate as a shock wave near the surface of the debris pile.