拉森火山國家公園

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拉森火山國家公園
IUCN 分類二：國家公園

位於:	美國加利福尼亞州
最近的城市:	雷丁
經緯度:	北緯40°29′17″，西經121°30′18″
占地:	106,000英畝 (429平方公里)
創建於:	1916年 8月15日
訪客數:	1,250,000人 (2003)
所屬轄區:	美國國家公園管理局

拉森火山國家公園(英語：Lassen Volcanic National Park)是位於美國加州北部的國家公園。整個國家公園中最主要的景觀就是拉森火山(也譯作拉森峰)，是世界上最大的穹頂火山，也是喀斯喀山脈中最南端的火山。

在拉森火山國家公園中，其火山活動依然顯著，包括大量的泥火山、發出惡臭的噴氣孔及溫泉。拉森火山國家公園是世界上少數幾個能找到所有火山類型的地區，包括穹頂、盾狀火山、火山渣錐及層狀火山。

要前往公園，可以藉由California State Route 44及California State Route 36前往。CA-89公路是穿越公園的南北向公路，但因降雪量龐大，只在仲夏到早秋期間開放。

[编辑] 歷史

印第安人早在殖民者發現拉森火山前就居住在此處了。印地安人們探索此區，發現拉森火山到處都是火與水，就認為它有一天會炸開。

Inconsistent newspaper accounts reported by witnesses from 1850-1851 described seeing "fire thrown to a terrible height" and "burning lava running down the sides" in the area of Cinder Cone. As late as 1859 a witness reported seeing fire in the sky from a distance, attributing it to an eruption. Early geologists and volcanologists who studied the Cinder Cone concluded the last eruption occurred between 1675 and 1700. After the eruption of Mt. St. Helens in 1980, the USGS began reassessing the potential risk of other active volcanic areas in the Cascade Range. Further study of Cinder Cone estimated the last eruption occurred between 1630 and 1670.

Lassen Peak and Cinder Cone were declared United States National Monuments in 1907 by President Theodore Roosevelt.

Brokeoff Mountain, Lassen Peak, and Chaos Crags. The area of Lassen Peak that was lost during the 1914-15 volcanic event is clearly visible in this picture.

Starting in May 1914 and lasting until 1921, a series of minor to major eruptions occurred on Lassen. These events created a new crater, and released lava and a great deal of ash. Amid this volcanic activity, Lassen Volcanic National Park was created on August 9, 1916.

1974年，美國國家公園管理局接受美國地質調查所(USGS)的建議，關閉了曼薩尼塔湖的遊客服務中心及住宿設施。研究資料顯示，這些建築物位於一個危險地區，假若發生地震或火山爆發，從混沌崗(Chaos Crags)來的落石或火山碎屑流會襲擊這個區域。只有一個地震測站被留下。

[编辑] 氣候

因為拉森火山國家公園是處於中高海拔地區，在7500呎以下，其氣候大體來說是冬冷夏溫。高於這個高度，氣候非常寒冷，連夏天都不太熱。 Precipitation within the park is high to very high due to a lack of a rain shadow from the Coast Ranges. The park gets more precipitation than anywhere in the Cascades south of the Three Sisters. Snowfall at the Lassen Peak Chalet at 6700 ft. is around 430 inches despite facing east. Up around Lake Helen, at 8200 ft. the snowfall is around 600-700 inches, making it probably the snowiest place in California. In addition, Lake Helen gets more average snow accumulation than any other recording station in the Cascade range, with a maximum of 178 inches. ([1]).

[编辑] 地質學與地理學

Main article: Geology of the Lassen area

Lassen Peak is made of dacite and is the world's largest lava dome. The volcano sits on the north-east flank of the remains of Mount Tehama, a stratovolcano that was a thousand feet higher than Lassen and 11 to 15 miles wide at its base. After emptying its throat and partially doing the same to its magma chamber in a series of eruptions, Tehama collapsed into itself and formed a two-mile wide caldera in the late Pleistocene. Since that time the remains of Tehama have been heavily eroded.

On the other side of the present caldera is Brokeoff Mountain (9235 feet), which is an erosional remnant of Mount Tehama and the second highest peak in the park. Mount Conrad, Mount Diller, and Pilot Pinnacle are also remnant peaks around the caldera.

Sulphur Works is a geothermal area in between Lassen Peak and Brokeoff Mountain that is thought to mark an area near the center of Tehama's now-gone cone. Other geothermal areas in the caldera are Little Hot Springs Valley, Diamond Point (an old lava conduit), and Bumpass Hell (see Geothermal areas in Lassen Volcanic National Park).

Broken face of Brokeoff Mountain

The magma that fuels the volcanoes in the park is derived from subduction off the coast of Northern California.

Cinder Cone and the Fantastic Lava Beds, located about 10 miles northeast of Lassen Peak, is a cinder cone volcano and associated lava flow field that last erupted about 1650. It created a series of basaltic andesite to andesite lava flows known as the Fantastic Lava Beds.

There are four shield volcanoes in the park; Mount Harkness (southwest corner of the park), Red Mountain (at south-central boundary), Prospect Peak (in northwest corner), and Raker Peak (north of Lassen Peak). All of these volcanoes are 7000-8400 feet above sea level and each are topped by cinder cone volcanoes.

During ice ages, glaciers have modified and helped to erode the older volcanoes in the park. The center of snow accumulation and therefore ice radiation was Lassen Peak, Red Mountain, and Raker Peak. These volcanoes thus show more glacial scarring than other volcanoes in the park.

[编辑] 火山活動

主條目在拉森火山。

拉森火山是北美洲的90餘座活火山之一。它在1914年的活動，是美國本土在聖海倫山爆發前的最後一次火山爆發。拉森火山及其北方的混沌崗(Chaos Crag)是一個位在火山高地上的大型穹頂，由英安岩構成。火山南面有許多地熱活動的跡象，包括泥火山、溫泉及噴氣口。而熔岩流遺跡及火山錐渣主要分布於火山東面。

噴氣口

溫泉

泥沸泉

[编辑] 參考資料

Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7