The 2004 outburst flood at Glaciar Perito Moreno, Argentina
The 2004 outburst flood at Glaciar Perito Moreno, Argentina
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2004 年阿根廷佩里托莫雷诺冰川溃决洪水
DOI：
10.3189/172756504781829792
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发表时间：
2004
影响因子：
3.4
通讯作者：
C. Warren
中科院分区：
文献类型：
--
作者：
Guillermo A. Chinni;C. Warren
阿根廷佩里托莫雷诺冰川 2004 年爆发洪水 佩里托莫雷诺冰川（南纬 508280，西经 738020）面积 259 平方公里，是 Hielo Patagonico Sur（巴塔哥尼亚冰原南部）东部主要出口冰川之一。它终止于一个活跃的地面崩解前缘，长约 5 公里，高 55-80 m，在普遍裂隙的终点区域，表面速度达到 800 毫安（Rott 等，1998 年；Chinni，2004 年）。它流经并一分为二阿根廷湖的内峡湾，北端注入洛斯坦帕诺斯运河，南端注入布拉索里科。终点站的东端间歇性地登陆麦哲伦半岛。该冰川众所周知，部分是因为它是巴塔哥尼亚的主要旅游目的地之一，部分是因为它在 20 世纪曾多次爆发洪水。当终点站前进到麦哲伦半岛形成冰坝，将阿根廷湖的南臂与湖体主体隔开时，就会发生这种情况。然后水位上升，直到大坝最终溃决导致灾难性的排水。没有证据表明这些周期性进展与激增型行为有关。第一次有记录的洪水爆发发生在 1917 年。在此之前，洪水持续了至少 18 年的稳定前进，期间所有邻近的冰川都从小冰期最大值迅速退缩。 Warren (1994) 认为，20 世纪初的这一进步是对小冰期降温的延迟反应，这是由于崩解动力学和沉积之间的相互作用造成的。 1917 年至 1988 年间，共有 16 家工厂关闭，持续时间从数月到 3 年不等。水坝通常在冬末或早春形成，溃坝发生在夏末（3 月至 4 月）。 Brazo Rico 和 Brazo Sur 蓄水湖臂的水位上升了 10-26 m，造成大面积洪水并形成暂时扩大的湖泊，面积达 150 km。水压和融化的结合最终会形成穿过冰坝的地下管道和/或冰川管道，当大坝崩溃时，这些管道会迅速演变成地下隧道。然后，爆发会在几小时到几天的时间内排出约 3.0-4.0 公里的水。在排水过程中，隧道因熔化和崩解而迅速扩大，随后隧道顶板塌陷。突如其来的洪水使长约100公里的阿根廷湖水位上升了几米，淹没了沿岸的农田、道路和建筑物，有时还损坏了圣克鲁斯河上的桥梁，这条河在其东端排干该河。从 1915 年到 1993 年，终点站的平均位置几乎没有变化（Aniya 和 Skvarca，1992；Warren，1994）。在几乎所有巴塔哥尼亚冰川持续退缩的一个世纪里，这种长期保持的稳定性主要可以通过平衡线附近冰川表面的陡峭来解释，这使得冰川对气候变化不敏感，也可以通过相对较高的崩解通量与净积累的比率来解释（Rott等，1998）。从 1966 年到 1988 年，截流以准周期 4 年模式发生，从截流到大坝溃决，湖泊的形成通常需要大约 2 年的时间，随后又需要 2 年时间才能形成下一个大坝。然而，从 1988 年到 2003 年，没有发生过关闭事件。冬季确实进入了半岛，但水继续通过海岸线附近的冰下管道排出。然而，2003 年冬季的洪水确实形成了一座有效的大坝。布拉索里科的水位从 11 月开始上升，到 2004 年 2 月下旬，湖水已上涨 6.0 m。随后15天，天气温暖晴朗，堰塞湖水位以0.3md的速度上升，达到蓄水前水位10.5m。到那时，与之前关闭期间一样，一条隧道已开始在舌头南侧形成，预计大坝将在四月份溃坝。然而，3 月 11 日下午，观察到水从大坝下方排出并从北侧涌出。随着舌头南北两侧的初期隧道迅速扩大，大坝于 3 月 12 日上午破裂。随后，巨大的地下隧道发生了雷鸣般的水流排放（图 1）。由于水线处的机械和热侵蚀破坏了侧壁，导致隧道内和隧道附近频繁发生堵塞，隧道的尺寸迅速增大。到3月13日上午，隧道长度已被拆除约50%，隧道顶板厚度也大大减少，但原大坝南侧变化不大。尽管排水率随后逐渐下降，但持续的热机械侵蚀和崩解继续增加了拱门的尺寸，直到 3 月 14 日 1910 时，隧道顶部突然发生壮观的塌陷，留下冰墙矗立在狭窄的通道两侧（图 2）。突如其来的洪水对阿根廷湖沿岸造成了影响，水位连续几天上涨了 4.5 m。尽管破裂来得突然且出人意料，但该事件的消息传播得如此之快，以至于在三天内估计有 10 000 名游客前来观看这一奇观。这次最新的溃决事件的许多方面都与 20 世纪蓄水过程中观察到的序列一致，包括大坝形成和决堤的时间和机制。然而，2003/2004年修建的大坝是有记录以来寿命最短的大坝之一，将湖水位上升的幅度限制在远低于通常发生的水平。有趣的是，佩里托莫雷诺冰川的破裂是由冰川学杂志，卷。 50、171号，2004年
The 2004 outburst flood at Glaciar Perito Moreno, Argentina Glaciar Perito Moreno (508280 S, 738020 W), with a surface area of 259 km, is one of the major eastern outlet glaciers of Hielo Patagónico Sur (southern Patagonia icefield). It terminates at an active, grounded calving front some 5 km long and 55–80m high, with surface velocities reaching 800ma in the pervasively crevassed terminus area (Rott and others, 1998; Chinni, 2004). It flows across and bisects an inner fjord of Lago Argentino, the northern front calving into Canal de los Témpanos and the southern front into Brazo Rico. The eastern point of the terminus intermittently comes ashore onto Peninsula Magallanes. The glacier is well known, partly as one of Patagonia’s primary tourist destinations and partly as a result of its 20th-century history of repeated outburst floods. These occur when the terminus advances onto Peninsula Magallanes to form an ice dam which cuts off the southern arms of Lago Argentino from the main body of the lake. Water levels then rise until the eventual failure of the dam precipitates catastrophic drainage. There is no evidence that these periodic advances are related to surge-type behaviour. The first recorded outburst flood occurred in 1917. This followed at least 18 years of steady advance during a period when all neighbouring glaciers were retreating rapidly from Little Ice Age maxima. Warren (1994) suggested that this early 20th-century advance was a delayed response to Little Ice Age cooling caused by the interplay between calving dynamics and sedimentation. Between 1917 and 1988 there were 16 closures lasting from months to 3 years. Dams typically form in the late winter or early spring, with failure occurring in midto late summer (March–April). Water levels in the impounded lake arms of Brazo Rico and Brazo Sur rise 10–26m, causing extensive flooding and forming a temporarily enlarged lake with a surface area of 150 km. A combination of water pressure and melting eventually creates suband/or englacial conduits through the ice dam and these rapidly evolve into a subaerial tunnel as the dam fails. The outbursts then discharge some 3.0–4.0 km of water in the space of several hours to days. During drainage, the tunnel is rapidly enlarged by melting and calving, followed by collapse of the tunnel roof. Outburst floods raise the level of Lago Argentino, a lake some 100 km long, by several metres, inundating farmland, roads and buildings along the shore, and sometimes damaging bridges over Rı́o Santa Cruz, the river which drains the lake at its eastern end. From 1915 to 1993 the average position of the terminus showed little change (Aniya and Skvarca, 1992; Warren, 1994). This long-maintained stability during a century when almost all Patagonian glaciers consistently retreated (Warren and Aniya, 1999) can be explained primarily by the steepness of the glacier surface near the equilibrium line, which renders the glacier insensitive to climate change, and also by the relatively high ratio of calving flux to net accumulation (Rott and others, 1998). From 1966 to 1988, closures occurred in a quasi-cyclic 4 year pattern, with lake build-up typically taking about 2 years from closure to dam failure followed by 2 years before the formation of the next dam. However, from 1988 to 2003 no closures occurred. Winter advances onto the peninsula did occur, but water continued to drain through subglacial conduits near the shoreline. The winter advance of 2003 did, however, form an effective dam. The water level in Brazo Rico began rising in November, and by late February 2004 the lake had risen 6.0m. In the following 15 days, which was a period of warm, sunny weather, the level of the dammed lake rose at a rate of 0.3md to reach 10.5m above the pre-impoundment level. By then, as during previous closures, a tunnel had begun to form on the southern side of the tongue, and dam failure was anticipated during April. However, during the afternoon of 11 March, water was observed to be draining underneath the dam and emerging on the northern side. Following rapid enlargement of incipient tunnels on both the northern and southern flanks of the tongue, the dam ruptured on the morning of 12 March. Thunderous water discharge then ensued through a large subaerial tunnel (Fig. 1). The tunnel rapidly grew in size as mechanical and thermal erosion at the waterline undermined the side-walls, initiating frequent blockfalls within and adjacent to the tunnel. By the morning of 13 March, some 50% of the length of the tunnel had been removed and the thickness of the tunnel roof was much reduced, but the southern side of the former dam was little changed. Although the rate of water discharge then progressively decreased, ongoing thermomechanical erosion and calving continued to increase the size of the archway until the tunnel roof suddenly and spectacularly collapsed at 1910h on 14 March, leaving walls of ice standing either side of a narrow channel (Fig. 2). The outburst flood had impacts all around the shores of Lago Argentino as water levels rose by as much as 4.5 m for several days. Despite the sudden and unexpected onset of the rupture, news of the event spread so rapidly that an estimated 10 000 tourists came to watch the spectacle during the 3 days. Many facets of this latest outburst event conform with the sequence observed during 20th-century impoundments, including the timing and mechanisms of dam formation and rupture. However, the 2003/04 dam was one of the shortest-lived on record, restricting the magnitude of lakelevel rise to much less than has commonly occurred. It is of interest that ruptures at Glaciar Perito Moreno are initiated Journal of Glaciology, Vol. 50, No. 171, 2004