José Juan Zamorano

Paraglacial and postglacial debris flows on a Little Ice Age terminal moraine: Jamapa Glacier, Pico de Orizaba (Mexico)

The study area is located on the northern face of Pico de Orizaba (Mexico, 5700 m ASL), on the terminal moraine of Jamapa Glacier, which dates from the Little Ice Age. Large debris flows are recurrent on the proglacial ramp. The comparison of lichen colonies growing on the deposits of the flows reveals that two generations of flows are present: an old one and a very recent one that occurred between 1994 and 1995. Studies were made of the sedimentologic characteristics of the flows and ground temperatures were recorded to a depth of 70 cm on the floor of the channels. Comparison of the lichen-growth on the exposed surfaces of the deposits led to the relative dating of the older debris flow, which is associated with the beginning of the retreat of the glacier and the saturation of the terminal moraine deposits by meltwater. The more recent flow has less transport capacity and is identified with the formation of an impermeable layer of permafrost that covers the bottom of the channel of the old debris flow. The permafrost layer formed when snow accumulations on the bottom of the channel were covered by ash that fell from the slopes.

The impact of present lahars on the geomorphologic evolution of proglacial gorges: Popocatepetl, Mexico

Abstract Popocatepetl (19°03′N, 98°35′W; 5450 m) is located 70 km southeast of Mexico City. The volcano resumed its eruptive activity in 1994 with emissions of pyroclasts that partially melted the glacier located on the north face. The sudden release of water generated large lahars that flowed downslope though proglacial gorges. This paper examines the geomorphologic evolution of these gorges since 1992 and focuses particularly on the landforms created by the most recent lahars of July 1997. The research suggests that the transport capacity of the lahars has increased despite the fact that the sediments they carry originate in deposits formed by earlier processes. The presence of continuous permafrost in the area is a key factor in the formation of lahars.

Glacier retreat during the recent eruptive period of Popocaté petl volcano, Mexico

Abstract Popocatépetl (19°02’ N, 98°62’W; 5424 m) is one of the largest active stratovolcanoes in the Transmexican Volcanic Belt. A glacier located on the north side has undergone severe ablation since the volcano reinitiated eruptive activity in December 1994. In our study, we calculate the extent of the glacier recession and the loss in glacial mass balance during the period of greatest laharic activity (1994–2002), using photogrammetric treatment of 20 pairs of aerial photographs. The results indicate that from November 1997 to December 2002, the glacier released approximately 3 967 000 m3 of water. A period of intense glacier melting occurred from 4 November 2000 to 15 March 2001 during which time 717 000 m3 of water was released. Much of the melting was attributed to the pyroclastic flow that took place on 22 January 2001 and produced a 14.2 km lahar with 68 000 m3 of water. Among the many types of volcanic events, pyroclastic flows were the most effective in causing sudden snowmelt, although small explosions were also effective since they deposited incandescent material on the glacier. The collapse of the plinian columns covered the glacier with pyroclasts and increased its volume. The existence of control points for georeferencing and a knowledge of the topography underlying the glacier previous to the eruption would have provided more accurate and useful results for hazard prevention.

Unchanged surface morphology in debris-covered glaciers and rock glaciers in Tröllaskagi peninsula (northern Iceland)

Abstract This paper analyses changes in the surface morphology of rock and debris-covered glaciers in the Holadalsjokull and Fremri-Grjotardalur cirques near Holar village in the Trollaskagi peninsula (northern Iceland) (65°43′55″N; 19°06′49″W, 160 m), to understand the dynamics and climatic significance of these landforms. The study includes an analysis of historical aerial photographs from 1946 to 2000. The aim was to evaluate surface changes in these landforms and obtain the horizontal displacement and elevation changes of large boulders and linear features (ridges and furrows) at each date. In addition, the surface elevation differences between 1980 and 1994 were obtained from digital elevation models. The horizontal displacement results obtain a mean velocity of 0.33 m yr−1 and an average elevation difference of −0.72 m for the boulders, with the linear features advancing 14.84 m during the period 1946–2000. Except for this slow mobility, no changes occurred in the surface morphology of these landforms during the 54 years. The low displacement rates of boulders and linear features, together with the surface lowering processes observed in these landforms, indicate that widespread melting is the most important activity in the debris-covered and rock glaciers in Trollaskagi. This is confirmed by the recent formation of collapse depressions.