Postglacial chronology of large earthflows in south-central British Columbia
Notice bibliographique
Résumé
Fifty-three earthflows in south-central British Columbia were identified from an air photograph search and from a review of previous geologic reports. Many have parallel 'en echelon1 lateral deposits indicative of several movement phases during the postglacial period, and some have been active during the present century up to the time of the study. The purpose of this study was to date phases of earthflow activity during the postglacial period and relate them to climatic fluctuations. Earthflows in the study area are concentrated in serpentinised peridotite, basalt, sediments (mainly volcaniclastics), and other volcanics. Earthflows take place preferentially down dip in sediments and many are associated with fault lines. All earthflow materials, except those derived from serpentinised peridotite, weather to montmorillonite-rich material, and each yields a characteristic grain-size distribution. Earthflow gradient in the study area depends upon material type, indicating that earthflow texture and mineralogy govern shearing resistance and hence partially determine characteristic slope angles. Earthflow movement during the past 60 years was investigated using air photograph chronosequences dating back to 1928. Reactivations of six flows were identified in the period 1950 to 1960, and an analysis of precipitation records from four stations around the study area showed that the level of winter precipitation increased around 1950. It was concluded that the observed reactivation was a response to rising groundwater levels during a period of increased winter precipitation. Earthflow movement and climatic fluctuations over the last 200 years were investigated in an analysis of tree-ring width records at four sites. Moist phases were recorded in the periods 1800-1830, 1870-1920 and from 1945 to the present. Compression wood formation at three sites corresponded with moist phases, so it was concluded that, over the last two centuries, earthflow movement was probably coincident with phases of higher precipitation. A postglacial climatic chronology was inferred from published pollen analyses and from Neoglacial ice fluctuations, both within and outside the study area. New palynological data were collected from Red Mountain, a high elevation site in the west of the study area. These showed a two-phase cooling period following the close of the Hypsithermal. The first cooling period took place around 6-7,000 BP, and the second around 3,000 BP. Earthflow movement during the postglacial period was analysed using radiocarbon dates, tephrochronology, stratigraphy, carbonate accumulation, and earthflow morphology. Data from twenty-one sites showed that movement was concentrated mainly after 7,000 BP, and at several sites the stratigraphic position of the Bridge River tephra dated movement around 2,400 BP. It was concluded that, at this longer timescale, movement at many sites could be attributed to post-Hypsithermal climatic deterioration.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,004 | 0,004 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».