The evolution of several subalpine alluvial fans SE of the Jostedalsbreen ice cap was investigated based on their geomorphology and Schmidt-hammer exposure-age dating (SHD) applied to 47 boulder deposits on the fan surfaces. A debris-flood rather than debris-flow or water-flow origin for the deposits was inferred from their morphology, consisting of low ridges with terminal splays up to 100 m wide without lateral levees. This was supported by fan, catchment, and boulder characteristics. SHD ages ranged from 9480±765 to 1955±810 years. The greatest number of boulder deposits, peak debris-flood activity and maximum fan aggradation occurred between ~9.0 and 8.0 ka, following regional deglaciation at ~9.7 ka. The high debris concentrations necessary for debris floods were attributed to paraglacial processes enhanced by unstable till deposits on steep slopes within the catchments. From ~8.0 ka, fan aggradation became progressively less as the catchment sediment sources tended towards exhaustion, precipitation decreased during the Holocene Thermal Maximum, and tree cover increased. After ~4.0 ka, some areas of fan surfaces stabilized, while Late-Holocene climatic deterioration led to renewed fan aggradation in response to the neoglacial growth of glaciers, culminating in the Little Ice Age. These changes are generalized within a conceptual model of alluvial fan evolution in this recently-deglaciated mountain region and in glacierized catchments. This study highlights the potential importance of debris floods, of which relatively little is known, especially in the context of alluvial fan evolution.

中文翻译：

---

挪威南部 SE Jostedalsbreen 地区全新世冲积扇演化、Schmidt-hammer 暴露年龄测年和冰河旁碎屑洪水

Jostedalsbreen 冰盖的几个亚高山冲积扇 SE 的演化基于它们的地貌学和施密特锤暴露年龄测定 (SHD) 应用于扇表面的 47 个巨石沉积物。从它们的形态推断沉积物是泥石流而不是泥石流或水流起源，由低山脊组成，末端张开达 100 m 宽，没有侧堤。这得到了风扇、集水区和巨石特征的支持。SHD 年龄范围为 9480±765 至 1955±810 岁。在约 9.7 ka 的区域冰川消退之后，最大数量的巨石沉积物、最大的泥石流活动和最大的扇形加化发生在约 9.0 至 8.0 ka 之间。泥石流所需的高泥石浓度归因于流域内陡坡上不稳定的泥土沉积物增强了冰河边的过程。从~8.0 ka 开始，随着集水区沉积物源趋于枯竭，全新世热最大值期间降水量减少，树木覆盖率增加，扇形加化逐渐减少。在~4.0 ka之后，部分扇面区域趋于稳定，而晚全新世气候恶化导致扇面重新加积以响应冰川的新冰期生长，最终进入小冰河时代。这些变化在这个最近冰川消退的山区和冰川集水区的冲积扇演化的概念模型中得到了概括。这项研究强调了泥石流的潜在重要性，而泥石流对此知之甚少，