导读：奥林帕斯山火山口深约3公里，顶峰高26公里，平均高度22公里，是地球上珠穆朗玛峰的三倍。它的外形如同一个巨大的盾牌，奥林帕斯山底部的面积比英国还大，顶上的火山口能容纳两个伦敦还绰绰有余。奥林帕斯山总是位于活火山区，而且数百万年来它一直在增大。

对应考题：托福阅读机经(2010年3月27日)Passage 1

　　　　　http://www.yeeaoo.com/test/toefl/jj/toefl_jj_143707.html

Olympus Mons Volcano - Highest Point on Mars

Olympus Mons volcano is the highest point on Mars at an elevation of 21,229 meters (69,649 feet) above the Mars areoid (a reference datum similar to Earth's sea level). It is also the highest mountain in the solar system and the solar system's largest volcano. In this image, Olympus Mons is the largest volcano. Lava flows from Olympus Mons and its neighboring volcanoes have resurfaced the planet in this area. These lava flows are not heavily cratered, revealing that the eruptions which formed them occurred at a point in the planet's history that was after the heavy asteroid bombardment.

Olympus Mons is an enormous volcano. It stands about 25 kilometers (15.5 miles) higher than its surrounding landscape and it is over 500 kilometers (310 miles) in width. The map above has been enhanced to make topographic features more obvious. On that map, Olympus Mons looks steeper than it actually is.

Olympus Mons is a gently sloping shield volcano, much like the volcanoes that make up the Hawaiian Islands. If you were placed on the flank of Olympus Mons and not told that you were standing on the slope of the volcano, you could probably look around and think that you were standing on a gently sloping plain. You would see a gentle slope upwards in one direction and a gentle slope down in the opposite direction.

If you were placed on the rim of the summit crater and looked down the slope of the volcano, your horizon would be located on the volcano's flank. The volcano is that gently sloping and that immense.

Astrogeologists believe that plate tectonics processes on Mars are no longer active. Olympus Mons is thought to be located on a stationary "plate" over a deep hotspot. The stationary nature of the plate has kept the Olympus Mons fixed above the hotspot, allowing repeated eruptions to build it to a very great height.

In the vertical image from the Viking Orbiter Mission above a sharp change in slope can be seen as a light area that almost completely surrounds the volcano. This light area marks a steep cliff or escarpment about one to four kilometers in height. The origin of this escarpment is debated but remains unknown. Ideas of it being a product of faulting, erosion, landsliding and uplift have all been proposed.

中文背景：

奥林帕斯山(OlympusMons)是太阳系最高的火山，它位于火星上。奥林帕斯山火山口深约3公里，顶峰高26公里，平均高度22公里，是地球上珠穆朗玛峰的三倍。它的外形如同一个巨大的盾牌，奥林帕斯山底部的面积比英国还大，顶上的火山口能容纳两个伦敦还绰绰有余。奥林帕斯山总是位于活火山区，而且数百万年来它一直在增大。

奥林帕斯山是一座由于大量喷发和熔岩层叠堆积而形成的巨型火山，火星上的低引力和非常微弱的地表地质构造活动促使了这座巨大火山的形成，火山周边几乎都围绕有4千米长的悬崖峭壁，火星上的火山活动大约在200万年前停止，但是科学家不排除奥林匹斯火山将来会有重新“觉醒”的可能性。

奥林帕斯山高达二十五公里，基部宽约六百公里，顶部的喷火口直径达八十公里，为火星表面上最大的火山。从奥林帕斯山平缓的坡度和周围的熔岩原可看出，过去必定流出大量的熔岩而形成如今这个面貌。在地球上可供比较的最大地形是夏威夷的马那基山，只高出太平洋海床九公里，基部宽也只有二百二十五公里。为塔尔西斯穹丘最大火山。