Explaining the Formation of the Extraordinary Alaska Range

The Alaska Range boasts some of the world's most dramatic topography, including the over 20,000-foot Denali mountain (Mount McKinley). Geologists at Syracuse University are just beginning to understand how this extraordinary mountain range formed, explaining their findings in a new study.

A variety of factors contributed to the impressive mountains and exquisite terrains of the Alaska range, researchers say, among them earthquakes, plate tectonics, and the location of the curved Denali fault. This information can help scientists better understand "the evolution of our planet, how faults and mountain belts form, and why earthquakes happen," lead author Paul Fitzgerald said in a statement.

Using mapped surface geology, geophysical data, and thermochronology - time-temperature history of the mountain's rocks - Fitzgerald and his colleagues determined that much of Alaska's uplift and deformation began some 25 million years ago, when the Yakutat microplate first started colliding with North America. Furthermore, the Alaska Range's towering peaks are the result of "weak suture-zone rocks" between terranes, or distinctly different rock units.

Mountains may seem formidable, but they are contrastingly formed mostly from fractured rock units. Movement of these rocks along the range's Denali fault - which cuts across south-central Alaska - is what caused uplift of these mountains, which form and bend at the fault.

"The patterns of deformation help us understand regional tectonics and the formation of the Alaska Range, which is fascinating to geologists and non-geologists alike," added Fitzgerald.

In 2002, the Denali fault was the site of a 9.7-magnitude earthquake - the largest of its kind in more than 150 years. This catastrophic event helped shape the alternating asymmetrical topography along the fault.

"From our perspective, the earthquake has motivated analyses of why the highest mountains in the central Alaska Range occur south of the Denali fault and the highest mountains in the eastern Alaska Range occur north of the fault - something that has puzzled us for years," Fitzgerald said.

This and other findings were published in the journal Tectonics.