It’s a question that has puzzled geologists and Bob Dylan for a long time: “how many years can a mountain exist, before it’s washed to the sea?”
Now, a new study shows that changes in climate, particularly ice ages, can wash a mountain away to the sea faster than it can be built up by geologic forces. Over the years, the St. Elias mountains have eroded, with rocks soil and other sediments from the mountains eventually landing in the depths of the Gulf of Alaska. The researchers spent over a decade drilling into these sediments to get a better picture of how erosion rates changed through the mountains’ history.
Of course, on some level, the findings are not a total surprise. While there are mountains here on Earth that are growing right now, they are always acted on by erosive forces. Wind, water, ice and gravity pull and prod at a mountain’s mass, gradually turning even high peaks like the Himalayas into softly rolling mountains like the Appalachians. What wasn’t clear before was how quickly erosion could tear down what tectonics were building up.
Researchers working on the new study looked at the St. Elias mountain range in Alaska, which has been growing at more or less a consistent rate for the past 6 million years, pushed towards the sky by the collision of the Pacific and North American tectonic plates. And though the rate at which the mountain range grew stayed constant, the climate in that region changed a lot over the years.
In the Gulf of Alaska, the researchers found that the volume of sediments eroding from the St. Elias mountains increased suddenly about one million years ago. During that time, the Earth went through a cooler period where ice ages were more common. In the past million years, the authors write, erosion outpaced the growth of the mountain range by 50 to 80 percent. The finding shows that in some cases, changes in climate can dramatically change geologic processes.
“Humans often see mountain ranges as static, unyielding parts of the landscape,” John Jaeger said in a statement. “But our work has shown that they are actively evolving along with and responding to Earth’s climate, which just shows how truly dynamic and coupled this planet is.”