Rapid and large-scale landscape modification caused by the draining of a glacier-dammed lake in British Columbia, Canada
Notice bibliographique
Résumé
River terraces are ubiquitous in the formerly glaciated valleys of British Columbia, where they are commonly interpreted as products of Holocene incision of paraglacial valley fills. In this paper, we describe and interpret terrace sequences on the former floor of glacial Lake Fraser, the largest Late Pleistocene glacier-dammed lake in British Columbia. Postglacial terraces up to 120 m above the present lower Nechako and Fraser River valley floors are the dominant landforms within the former lake basin. In this paper, we focus on the Nechako River terraces between Stuart River and Prince George, a distance of about 85 km. Our reconstruction and analysis are based on high-resolution lidar imagery and field investigation of sediments exposed beneath the terraces. The highest, unpaired terraces are mainly erosional landforms developed on glacial Lake Fraser glaciolacustrine sediments, but are ornamented with low biconvex flood bars and linear erosional channels. As water drained rapidly eastward out of the lake, thin flows of fluidized lacustrine silt and sand derived from adjacent valley walls were deposited on the highest terraces and flood dunes formed below the lowest paleo-lake shorelines. At the same time, huge amounts of sediment were stripped from the emergent valley walls by landslides and gullying. This large and rapid flux of sediment provided thick gravel and sand that underlie lower Nechako Valley terraces. The lowest terraces have meandering channel forms that are markedly different from the streamlined high terrace surfaces. About 200 kettles in six clusters on mid- and low-level terraces in Nechako Valley mark locations of ice blocks that calved from the stagnating front of the remnant Cordilleran Ice Sheet to the west and became stranded on the floor of glacial Lake Fraser. The distribution of the kettles shows that Nechako and, by inference, Fraser rivers were flowing within a few metres of their present levels within years to several decades after glacial Lake Fraser drained, which challenges the common assumption implicit in the paraglacial model that the terraces developed more slowly throughout the Holocene. • The study provides a new perspective on the paraglacial cycle. • Emptying of Late Pleistocene ice-dammed lake in British Columbia transformed the lake basin. • Aggradation of valleys triggered by regional slope instability and liquefaction. • Kettles on terraces constrain times of terrace abandonment. • Terraces in the lake basin formed rapidly when the lake emptied, not throughout the Holocene.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 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 tête enseignante, 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 ».