Initial Publication Date: August 18, 2014

Preparing for the Voyage

Part C: Where Are We Going?

Expedition 341 is heading for the southern coast of Alaska. Alaska is one of the most interesting places for geologists because it is composed of pieces of Earth's crust that formed in different parts of the world and were later transported to their current location. The map below shows the pieces of crust that make up the Alaskan landmass, forming a mosaic pattern across the state. Geologists refer to these crustal pieces as terranes group of rocks having a common age or origin. , and they have been shaping Alaska's landscape for the past 200 million years or so.

Like a patchwork quilt, each terrane is unique. The composition and structure of Alaska's terranes differ due their different geologic histories. The youngest terrane to arrive is called the Yakutat terrane, and it continues to move northward, jamming itself into the North American tectonic plate, creating the beautiful St. Elias Mountains.

One of the drilling sites of the expedition is about 70 miles south of the Alaskan coast. On a clear day, you can see the snow-capped peaks of the Chugach and St. Elias Mountain Ranges in the distance. That we can see these mountains from so far away reflects their enormity. Southern Alaska is home to the three highest mountains in North America: Mt. McKinley (20,320 ft.), Mt. Logan (19,551 ft.), and Mt. St. Elias (18,008 ft.). This grand landscape began forming approximately 30 million years ago due to the collision of the Pacific and North American tectonic plates.

As the tectonic plates collide, layers of rock are progressively forced, or thrusted, on top of each other. Thrust faults a thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. build up stress in the rock layers, and when the stress becomes too great for the faults to manage, the layers slip and slide against each other and a vast amount of energy is released in the form of earthquakes. Alaska is no stranger to earthquakes. It is the most seismically active state in the U.S. The magnitude 9.2 earthquake in 1964 is the second-largest quake ever recorded in the U.S. Movement along thrust faults continues as crustal plates collide, and rocks are continuously forced upward. This upward movement (called exhumation he uncovering or exposure through erosion of a former surface, landscape, or feature that had been buried by subsequent deposition.) of rocks is also referred to as "uplift" and is an integral process in the formation of mountain belts.

How is glacier advance and retreat related to sedimentation rates, climate change, and the formation of mountain belts? This is a central question that expedition scientists are attempting to answer. To collect data, the JR will visit five sites in the Gulf of Alaska. But why did scientists choose these particular sites? To understand why, listen to an explanation by lead scientist Ken Ridgway.

Checking In

1: Alaska is so interesting from a geologic point of view because__________________.
[INCORRECT]Alaska has many glacier and ice but it is not covered by ice sheets
[CORRECT]That's right! Alaska has a great diversity of different terranes for geologists to investigate.
[INCORRECT][feedback]Other states have more impressive mountains and mountain ranges.[end feeback]
[INCORRECT]Alaska has had some great earthquakes but that is not what makes it so interesting geologically.


Now that you have an idea of the goals of the JOIDES Resolution, are more familiar with the scientific objectives of Expedition 341, and have heard why scientists are visiting the sites that Exp. 341 will visit in the Gulf of Alaska, make a prediction about how the sediments collected along Exp. 341's journey might change from the first drilling site in the deep ocean to the drilling sites closer to land.

Discuss with your group and then compare your responses with those of the rest of your class.