Dań Zhùr (Donjek) Glacier, located in the St. Elias Mountains, Yukon, is a surge-type glacier that undergoes cyclical periods of rapid advance over a period of ~1-2 years, followed by retreat for a period of ~10 years (Kochtitzky et al., 2019). Dań Zhùr Chù’ (Donjek River) runs perpendicular to the terminus of the glacier and past surges have, at times, caused the terminus to advance enough to block the river, leading to the formation of an ice-dammed lake (Kochtitzky et al., 2020). The glacier most recently surged between 2012 and 2014, and since then Dań Zhùr Lake has drained three times: in 2017, 2018 and 2019. When a glacier dam fails, the drainage of the lake can be catastrophic and cause flooding downstream. In the case of Dań Zhùr Lake, the most recent drainage event occurred on July 13th, 2019, when the ~2.45 km2 lake drained in less than 36 hours and created an ice canyon through the glacier terminus. Time-lapse cameras and pressure sensors were used to capture the drainage event, and air photos taken during the melt season (June and September) were used to construct digital elevation models (DEMs) of the glacier terminus, lake, and lake basin. The method of drainage for the 2019 event was determined to be flotation of the terminus, leading to rapid subglacial drainage of the lake. There were also noticeable changes in water extent downstream during the 2019 event, meaning that there is a potential risk to downstream recreational users. Because of the formation of a large ice canyon after the 2019 drainage, it is very unlikely that that the lake will reform until the next surge, which is anticipated to occur around 2024. Following that surge, the size of Dań Zhùr Lake is expected to increase during the next quiescent phase, as the continued glacier recession will expose a larger basin for the lake to form in, and flotation will continue to be a likely mechanism for drainage. However, in the long term it is unlikely that ice-dammed lakes will continue to form at Dań Zhùr Glacier, as there is a trend of the maximum terminus extent during each surge being smaller than the previous one, meaning that the glacier will no longer block the flow of Dań Zhùr Chù’.

Thesis (Ph. D.)--University of Washington, 1988. / Map on folded leaf in pocket. Vita. Bibliography: leaves [133]-134.

Glacier surges are periods of dynamic instabilities which result in semi-regular alternating periods of slow flow, termed the quiescent phase, and fast flow, termed the active phase. This study uses remotely sensed imagery, digital elevation models, glacier velocity datasets, and in situ oblique photographs to reconstruct the surge history and dynamics of Fisher Glacier to better characterize surging in the southwest Yukon and assess the risk posed by this glacier’s surges on surrounding regions. Fisher Glacier has previously been identified as a surge-type glacier but, until now, it had not been the focus of any detailed studies. We find evidence that Fisher Glacier underwent two surges during the study period from 1948 to 2022. Visual analysis of characteristic surge features on the glacier surface show that the glacier was in quiescence from <1948 to at least 1963. In 1972, an advanced terminus position, intense surface crevassing, and high point velocities suggest that a surge had recently terminated, corroborating a previous report of a surge occurring around 1970. This was followed by a 40-year quiescent phase from ~1973-2013 during which the terminus underwent consistent retreat, totaling a terminus-wide average of 2058 ± 8 m (up to 3567 ± 8 m in certain sections). Velocities during the quiescent phase were low (generally <50 m yr⁻¹), but underwent a slow multidecadal increase starting around 1985, spreading from the center of the glacier towards the head and the terminus. A pre-surge buildup phase beginning in ~2008-2010 resulted in velocities of up to ~200 m yr⁻¹. The active phase of the surge initiated in winter 2013/14 and was characterised by a velocity increase to ~1500 m yr⁻¹ that propagated both up- and down-glacier from the surge nucleus in the mid-region (~22 km upglacier from the terminus). Velocities peaked at >2100 m yr⁻¹ in the winter/early spring of 2016 at ~12 km from the terminus. The surge resulted in a mean terminus-wide advance of 868 ± 8 m, intense surface crevassing and a downglacier transfer of mass from the reservoir zone to the receiving zone. The terminus area increased in elevation by a mean of ~80 m. In July 2016, the surge rapidly terminated within a period of ~1 month, although velocities at the head and the terminus took a few more months to slow to quiescent values. Since then, average annual velocities along the centerline have been lower than pre-surge velocities, the crevasses have closed up, and the rate of ice surface elevation change has been negative across the entire glacier. Fisher Glacier’s surge dynamics suggest predominantly hydrologically controlled surging, but with some aspects more representative of thermally controlled surging. Thus, we propose that more than one mechanism might be at play in controlling its surges, although further research is required to confirm this. Under current climate conditions, it is unlikely that Fisher Glacier could dam the nearby Alsek River and cause a glacier lake outburst flood.

No description available.

Despite their relatively small ice volume, mountain glaciers contributed nearly one third of global sea level rise since 2000, with one of the largest total mass loss rates (73 ± 17 Gt a-1) occurring in the Yukon-Alaska region. However, there is uncertainty surrounding how ice dynamics are being affected by such losses and whether glacier flow instabilities, such as surges, are changing in a warming climate. The St. Elias Mountains contain a major cluster of surge-type glaciers, yet a detailed analysis of their characteristics, including surge frequency, morphology, magnitude, and propensity over time has not been undertaken on a regional basis. This thesis presents a review of surging behaviour and an updated surge event inventory in the St. Elias Mountains, and quantifies the processes influencing both surging and non-surging glacier velocity variability using a variety of remote sensing and field measurements. An updated inventory of surge-type glaciers and observed surge events (1874-2023), compiled from existing inventories, recently published articles, and velocity analysis, is used to analyze the characteristics of surge-type glaciers and velocity patterns during surge events. The modern (1985-2023) trends in annual, winter and summer velocities of selected surge-type glaciers is then used to classify dynamic instability events into 4 categories. While 231 glaciers were classified as surge-type, only 42 were observed to have experienced rapid velocity events over the period 1985-2023, through either direct measurements or remote sensing observations. For glaciers with observed rapid velocity events, these predominantly fall into two categories: Alaskan-style surges with short active and quiescent phases, and glacier pulses, which are velocity accelerations that are limited in both magnitude and extent. An unnamed former tributary to Kluane Glacier underwent a dramatic surge from 2013-18. Using a combination of air photos, remote sensing and field observations, the characteristics and changes of ‘Little Kluane Glacier’ were reconstructed from the 1940s until 2021. While only the single full surge of 2013-18 was identified, it is likely that a partial surge of just the upper north arm occurred between 1963 and 1972. Repeat Digital Elevation Models (DEMs) and velocity profiles show that the recent surge initiated from the upper north arm accumulation area in 2013, which developed into a full surge of the main trunk from 2017-18. Terminus positions show long-term retreat from 1949-2017, followed by rapid advance of >2 km from May to September 2018, with surface velocities reaching a peak of ~3600 m a-1 in summer 2018 over the lower ablation area. This was likely enhanced by the drainage of supraglacial lakes and streams to the glacier bed through crevassing as the surge progressed. Changes in surface topography caused by initial mass movement, the resulting reorganization of the supraglacial hydrological system, and ponding of surface water, may drive a partial surge into a full surge, and therefore exert a direct control on glacier dynamics. In May 2016, Kaskawulsh Glacier underwent a dramatic proglacial hydrologic reorganization instigated by the rapid drainage of proglacial Slims Lake: as a result, water which previously drained north into Ä’äy Chú, (Slims River) toward Lhú’áán Män (Kluane Lake), was redirected south into Kaskawulsh River, eventually flowing into the Gulf of Alaska. A long-term (up to ∼120 year) record of terminus retreat, thinning and surface velocities from in-situ and remote sensing observations is used to determine the impact of this reorganization on glacier dynamics. After an initial deceleration during the late 1990s, terminus velocities increased at a rate of 3 m a-2 from 2000-12, while the area of proglacial Slims Lake increased simultaneously. The rapid drainage of the lake substantially altered the velocity profile of the adjacent glacier, decreasing annual velocities by 48% within 3 km of the terminus between 2015 and 2021, at an average rate of ∼12.5 m a-2. A key cause of the rapid drop in glacier motion was a reduction in flotation of the lower part of the terminus after lake drainage. This has important implications for glacier dynamics and provides one of the first assessments of the impacts of a rapid proglacial lake drainage event on local terminus velocities. The results of this study provide an examination of factors controlling glacier dynamics, as well as the characteristics of rapid glacier velocity events, in the St. Elias Mountains. This provides insights into the behaviour of mountain glaciers, how they are changing in a warming climate, controls on glacier surging, and the hazards they may pose for downstream communities, which are particularly vulnerable to disturbances.

The theme of this research is the use of prediction models of Integrated Autoregressive and type of moving average- ARIMA, along with the Autoregressive models of Conditional Heterokedastic-ARCH. The first class of models is used to describe the level and the second, the volatility of the series. Has, as main objective of this research, predict and analyze the variability of the flow of inputs of the Jaguari River, by means of linear and non-linear mathematical models, in order to assist in the management of water resources of the river and for power generation of pinch Furnas do Secret. This dissertation consists of two scientific articles that characterize the hydrological behavior of the Jaguari River, using to this end, mathematical models that provide predictions of the flows and the measurement of the periods considered atypical for the time series. In the first article, have chosen the model SARMA (1,0,1)(1,0,1)12-ARCH (1) able to represent the average and the variability of flows of the Jaguari River in m3s in 1942 to 2006 period. In the second article, we use mathematical models of forecasting, along with implementation of intervention analysis, investigation of hydrological behavior of flows in monthly periods January 1970 to December 2010. To do so, mathematical models adopted: Holt-Winters exponential smoothing (AEHW), ARIMA, ARCH models, and intervention analysis, concluding that the model SARMA (1,0,0)(2,0,0)12-ARCH(1) was selected to represent the average hydrological behavior and the variability of flows, in order to make forecasts, taking into account the selection criteria AIC and MAD. The ARCH model presented a degree of persistence is smaller than one, indicating that the flows, in a short time, will return to his usual level. Intervention analysis, increases were observed in the flows of 15,68 m3/s and 18,47 m3/s, during periods of November 1994 and December of 2009, possibly caused by climatic phenomena. However, it appears that the joint ARIMA modeling-ARCH and the incorporation of intervention analysis come to aid in the energy planning of PCH, in order to allow for great levels of power generation in the future. / O tema desta pesquisa é a utilização de modelos de previsão do tipo Autorregressivos Integrados e de Médias Móveis- ARIMA, juntamente com os modelos Autorregressivos de Heterocedasticidade Condicional- ARCH. A primeira classe de modelos tem a função de descrever o nível e o segundo, a volatilidade da série em estudo. Tem-se, como objetivo principal desta pesquisa, prever o nível e analisar a variabilidade da vazão de afluências do rio Jaguari, por meio de modelos matemáticos lineares e não lineares, com o intuito de auxiliar na gestão dos recursos hídricos do referido rio e para a geração de energia da pequena central hidrelétrica Furnas do Segredo. A presente dissertação consta de dois artigos científicos que caracterizam o comportamento hidrológico do rio Jaguari, utilizando, para isso, modelos matemáticos que proporcionam realizar as previsões das vazões e a mensuração dos períodos considerados atípicos durante a série temporal. No primeiro artigo, selecionou-se o modelo SARMA (1,0,1)(1,0,1)12-ARCH (1) capaz de representar a média e a variabilidade da série de vazões do rio Jaguari em m3/s no período de 1942 a 2006. No segundo artigo, utilizam-se modelos matemáticos de previsão, juntamente com aplicação da análise de intervenção, na averiguação do comportamento hidrológico das vazões em períodos mensais de janeiro de 1970 a dezembro de 2010. Para isso, adotaram-se modelos matemáticos: Alisamento exponencial de Holt-Winters (AEHW), modelos ARIMA genérico, modelos ARCH, e análise de intervenção, concluindo-se que o modelo SARMA (1,0,0)(2,0,0)12-ARCH(1) foi o selecionado a representar o comportamento hidrológico médio e a variabilidade das vazões, para, assim, realizar as previsões, levando em conta critérios de seleção AIC e MAD. O modelo ARCH apresentou um grau de persistência menor do que um o que indica que as vazões, em um curto espaço de tempo, retornarão ao seu patamar usual. Na análise de intervenção, observaram-se acréscimos nas vazões de 15,68 m3/s e 18,47 m3/s, durante os períodos de novembro de 1994 e dezembro de 2009, possivelmente ocasionados por fenômenos climáticos. Conclui-se que a modelagem conjunta ARIMA-ARCH e a incorporação da análise de intervenção vêm como forma de auxiliar no planejamento energético da PCH, de modo a permitir satisfatórios níveis de geração de energia elétrica futura.