GEOPHYSICS: Rising Rapidly Recently

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Science  27 Sep 2002:
Vol. 297, Issue 5590, pp. 2173b
DOI: 10.1126/science.297.5590.2173b

The Grand Canyon formed as the Colorado River cut through rocks of the Colorado Plateau and as the average elevation of the region increased by about 2 kilometers. The timing of the uplift has been debated: One estimate is that most of it took place during the past 5 million years; a second is that it began as early as 40 million years ago (Ma). This question not only bears on the age of the Grand Canyon but relates to the development of topography and climate throughout western North America, as well as the understanding of the mechanisms of uplift of this plateau and, through comparison, other plateaus worldwide.

Sahagian et al. provide a new estimate by looking at the size of air bubbles in basalt flows that erupted on the Colorado Plateau since 23 Ma. Simply put, the size of bubbles in a basalt flow depends primarily on the atmospheric pressure at the top of a flow and its thickness. Thus, the distribution of bubble sizes in flows of known thickness can be used to infer pressure and elevation. Analysis of many flows across the Colorado Plateau dating from 23 Ma indicates that the region experienced slow uplift (40 meters per million years) until about 5 Ma, and has risen five times as rapidly since then. - BH

Geology 30, 807 (2002).

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