Lava Channel Formation during the 2001 Eruption on Mount Etna: Evidence for Mechanical Erosion

We report the direct observation of a peculiar lava channel that was formed near the base of a parasitic cone during the 2001 eruption on Mount Etna. Erosive processes by flowing lava are commonly attributed to thermal erosion. However, field evidence strongly suggests that models of thermal erosion cannot explain the formation of this channel. Here, we put forward the idea that the essential erosion mechanism was abrasive wear. By applying a simple model from tribology we demonstrate that the available data agree favorably with our hypothesis. Consequently, we propose that erosional processes resembling the wear phenomena in glacial erosion are possible in a volcanic environment.

Figure 1

Aerial view of the Laghetto eruptive vent. The channel can be seen to the left of the pyroclastic cone. As indicated, the erosional feature (head of the channel) starts immediately at the emission vent. Its length (220 m) gives the scale of the picture. In the upper part, there is the lava field produced by the eruption of 2001.

Figure 2

The right bank of the channel. In the foreground the bottom of the channel can be seen. It is covered by the eroding lava flow. The incision of the channel renders visible the layered structure of the substratum. It is important to note that these layers, erupted a few days or hours before, were still rather soft and plastic. This is displayed by the uppermost layer folded inside the channel just after its incision.

Figure 3

Cartoon showing the mechanical erosion of the channel (not in scale). (a) Near the vent (less than 500 m), the preflow terrain consisted of thin layers of hot lava. (b) While moving down the slope the autoclastic lava flow carved out the soft parts of the substrate. (c) Situation after the flow had stopped. The channel floor is partially covered by lava of the eroding flow.