**1. Introduction**

The Cordillera Blanca (CB) is the most extensively glaciated mountain range in Peru [1] where the present-day climate is characterized by a distinct seasonality, with a dry season from May to September and a wet season from October to April. The seasonality is controlled by the oscillation of the inner-tropic convergence zone [2]. Seasonal temperature variations are small but vary significantly on a daily basis [2]. Wet season snow accumulation at high elevation and meltwater from glaciers are the main source of water [3] for the arid west coast of Peru during the dry seasons. Over the course of the 20th century, glacier mass has significantly contracted (e.g., [1,4–6]). Glacier volume loss may influence the stability state and dynamics of a glacier, as a result of a change of the thermal regime, stress state at the bed-ice interface, and associated changes in geometry. Numerous studies suggest that variations in glacier velocities are related to subglacial water pressures, which are controlled by seasonal meltwaters or infiltration following heavy rainstorms [7–14]. The supply of subglacial water is regulated by the extent of Firn coverage [15], as well as the characteristics of the subglacial drainage system. Pressurized subglacial water reduces the effective normal stress at the bed-ice interface, leading to reduced frictional resistance, and thus sliding rates are enhanced [11,15–17]. Detailed observational changes in a glacier's dynamics as well as its geometry, provide insights into whether a potentially hazardous glacier may develop a critical stability state, or conversely remain harmless [8].

**Citation:** Kos, A.; Amann, F.; Strozzi, T.; Osten, J.; Wellmann, F.; Jalali, M.; Dufresne, A. The Surface Velocity Response of a Tropical Glacier to Intra and Inter Annual Forcing, Cordillera Blanca, Peru. *Remote Sens.* **2021**, *13*, 2694. https://doi.org/10.3390/ rs13142694

Academic Editors: Paolo Mazzanti and Saverio Romeo

Received: 10 June 2021 Accepted: 6 July 2021 Published: 8 July 2021

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