ABLATION OF ICE‐CORED MORAINE IN A HUMID,MARITIME CLIMATE: FOX GLACIER,NEW ZEALAND

Depending on thickness, debris‐cover can enhance or reduce ablation, compared to bare‐ice conditions. In the geological record, hummocky moraines often represent the final product of the melt‐out of ice‐cored moraines, and the presence or absence of such moraine deposits can have paleoclimatic implications. To evaluate the effects of varying debris‐cover and climate on ice‐melt in a maritime mid‐latitude setting, an 11‐day ablation stake study was undertaken on ice‐cored moraine at Fox Glacier, on the western flank of the New Zealand Southern Alps. Ablation rates varied from 1.3 to 6.7 cm d^?1, with enhancement of melt‐rate under thin debris‐covers. Highest melt‐rates (effective thickness) occurred under debris‐cover of c. 2 cm, with ～3 cm being the debris thickness at which melt‐rates are equal to adjacent bare‐ice (critical thickness). Air temperature from nearby Franz Josef Glacier allowed for a simple degree‐day approach to ablation calculations, with regression relationships indicating air temperature is the key climatic control on melt. Digital elevation models produced from topographic surveys of the ice‐cored moraine over the following 19 months indicated that ablation rates progressively decreased over time, probably due to melt‐out of englacial debris increasing debris‐cover thickness. The morphology of the sandur appears to be strongly determined by episodic high‐magnitude fluvial flows (jökulhlaups), in conjunction with surface melt. Thus, ‘hummocky’ moraine appears to be a transient landform in this climatic setting.     

UPLAND AGRICULTURE IN THE MAYA LOWLANDS: ANCIENT MAYA SOIL CONSERVATION IN NORTHWESTERN BELIZE*

ABSTRACT. In the 1970s scholars began to accept Maya terracing as the manifestation of ancient intensive agriculture and large populations. We examine many ancient terraces and berms excavated in the Three Rivers region of Belize, synthesize the geography and suggest the intent of terracing across the Maya Lowlands, and analyze the history of terracing and soil erosion. Terraces occur in several slope positions and diverted and slowed runoff, to build up planting surfaces that could maximize soil moisture. The first accelerated soil erosion occurred during the Preclassic period (1500 b.c. ‐a.d. 250). Maya terracing started in the Early Classic period (a.d. 250–600) and spread across the Lowlands with the great population expansion of the Late/Terminal Classic period (a.d. 600–900). Thereafter, the Maya would largely forsake terracing. Though abandoned for a millennium, many terraces still function in today's tropical forests and burning milpas.