Complex interactions between meteorological parameters and the thermal regime of two tropical, high altitude crater lakes (Nevado de Toluca, Mexico).

Using long-term time series of meteorological and water-column parameters, the dynamics of two lakes separated by about 500 m from each other by a central lava dome, located at 4207 m above sea level in the volcano crater of Nevado de Toluca, Mexico were explored. Because of the strong wind-forcing previously measured on the volcano slope and the proximity of the lakes, wind-mixing was expected, with similar dynamics in both lakes. However, the meteorological parameters in the crater were significantly different than on the slope of the volcano, due to the dome and the high walls of the crater, which weakened wind speeds, modified wind direction, and reduced exposure to solar radiation by almost 20% in the crater compared to on the volcano slope. The rate and depth of thermal penetration into each lake differed by an order of magnitude, related with differential insolation due to crater wall shading, along with differences in transparency, most likely due to differential algal growth and suspended matter. At times, rapid surface cooling occurred during periods of reduced insolation and calm winds, leading to strong vertical convection and the formation of a characteristic step profile in the water column rather than the predicted wind mixing. These results are important for interdisciplinary studies of these and other alpine lakes and, in particular for biophysical coupling in these unique hydrological systems.

Natural Frequencies of seiches in Lake Chapala.

This research presents an analysis of the frequencies and vibration modes of the structure of the superficial seiches of Lake Chapala using mathematical modelling and measurements. The HAMSOM model was run with wind fields from coastal meteorological stations and for different lake storage levels. The lake water level measurements were carried out in two campaigns in 2003. An analysis of the surface seiches in the lake was performed using the fast Fourier transform method. A spectral analysis of lake water level measurements reveals seiches with periods close to 5.9, 3, 2, and 1.5 h. A comparison with the periods calculated by the HAMSOM model indicates that these periods correspond to superficial seiches of the fundamental longitudinal mode of the lake and the subsequent three modes. The lake has undergone important changes in its storage level over time. Therefore, we modelled it with storage levels from the isobaths 90 to 95 m and found that surface seiche periods decreased to 5.2 h.

Internal tsunami waves transport sediment released by underwater landslides.

Accelerated by gravity, submarine landslides transfer energy to the marine environment, most notably leading to catastrophic tsunamis. While tsunamis are thought to use less than 15% of the total energy released by landslides, little is known about subsurface processes comprising the rest of their energy budgets. Here, we analyze the first set of observations depicting a lake's interior response to underwater landslides and find that sediment transport is modulated by baroclinic waves that propagate along vertical gradients in temperature and sediment concentration. When traveling along a shallow thermocline, these waves can reach past topographic features that bound turbidity currents and thus expand the influence area of underwater landslides. With order of magnitude calculations, we estimate that observed thermocline internal waves received roughly 0.7% of available landslide energy and infer their contribution to homogenize the lake's thermodynamical properties by means of turbulent mixing. Lastly, we show that landslides in our data set modified the lake's intrinsic dynamical modes and thus had a permanent impact on its circulation. This suggests that measurements of subsurface wave propagation are sufficient to diagnose bathymetric transformations. Our experiment constitutes the first direct observation of both internal tsunami waves and turbidity current reflection. Moreover, it demonstrates that background density stratification has a significant effect on the transport of sediment after submarine landslides and provides a valuable reference for numerical models that simulate submarine mass failures.