Quick erosion
The rocks beneath our feet provide more than just cement. They also provide the footholds for dams that enable us to take maximum advantage of our water resources. It is important, of course, to be sure that dams are built on solid ground, which is one reason why geologists seek to understand what lies beneath our feet, from the metamorphic rock beneath the Central Mountain Range to the igneous formations of the East Coastal Range and the sedimentary layers in the west.
When the Shihmen Reservoir was in the planning stages some 30 years ago, a great controversy erupted over the question of dam design. Some favored an arch dam, while others argued for an embankment dam. Those against building an arch dam maintained that the sandstone geology of the Taoyuan tableland was not strong enough to withstand the tremendous pressure exerted by an arch dam. They summed up their argument as follows: "Put your left hand on my shoulder and your right hand on my neighbor's. Now lean against us. You're a dam, and we are mountains. As long as the mountains hold firm, you're ok. If we don't hold up, neither will you. That's precisely the problem. These mountains are not something you want to be leaning on."
The arch dam at Techi Reservoir in Taichung County did the engineers proud by escaping damage in the Chichi earthquake, for it was built on the very firm rock of the Mount Snow Range. Unfortunately, most of the island is made of sedimentary rock. Mount Chiuchiu in Shuangtung, which stands 400 to 500 meters high, is a loose mix of boulders and gravel that is especially vulnerable to the effects of an earthquake. In the words of geology professor Wang Hsin: "Just give it a good shake and it'll come crashing down."
No one knows better than geologists just how "collapsible" Taiwan is. During his days as a university student, Wang Hsin once looked all over Mount Ali for an area with some firm bedrock where he could study the mountain's geological strata, but everything he found was too crumbly to do him any good. The results of a study carried out in 1975 indicate that the rate of soil erosion in Taiwan's upper elevations is 44 times that of Asia as whole, 152 times that of North America, and 13.6 times that of the Alps. Rapid erosion is typical of young mountain ranges, and nowhere is this phenomenon demonstrated more clearly than in Taiwan. The pinnacle of achievement for Taiwan's highway engineers is undoubtedly Taiwan's three cross-island highways, each of which cuts east-west across the rugged mountains of the interior. It was a heady achievement for the engineers to blast and bore their way through the mountains, but nature seems to be exacting a measure of revenge, for it cannot be denied that these highways are extremely expensive to maintain due to the frequent landslides caused by heavy rains, especially during typhoons.
Rapacious logging of the coniferous forests of Mount Ali continued throughout the Japanese colonial period and on into the 1960s. When a heavy rain fell in the high mountains 50 years ago, it took a week for the water to arrive at the lower reaches of the various drainage basins. Today, however, a mountain downpour can cause a flood in Chiayi within two hours.
The geographer Chang Shih-chiao laments the wanton disregard of the Taiwanese people for the environment, and feels that we have exacerbated the damage of the recent earthquake through our own recklessness. In the end we are the ones who pay the price.
How many years of wind and rain did it take to create Taiwan's wildly weathered northeast coast?