Tom Savage: The Physical Geography of the Aleutian Islands, August 16, 2015


NOAA Teacher at Sea

Tom Savage

Aboard NOAA Ship Fairweather

August 6 – 23, 2018

 

 

Mission: Arctic Access Hydrographic Survey

Geographic Area of Cruise: Point Hope, northwest Alaska

Date: August 16, 2018

Weather Data from the Bridge

Latitude  68   38.8 N
Longitude – 166  23.8  W
Air temperature: 10 C
Dry bulb   10 C
Wet bulb  8.9 C
Visibility: 8 Nautical Miles   (8.8 miles)
Wind speed: 26 knots
Wind direction: east
Barometer: 1007  millibars
Cloud Height: 2 K feet
Waves: 6 feet

Sunrise: 6:33 am
Sunset: 11:51 pm

Physical Geography of Aleutian Islands

The Aleutian Islands are a product of a subduction zone between the North American and the Pacific Plate and known as the Aleutian Arc. Along this boundary, the Pacific Plate is being subducted underneath the North American Plate due to the difference in density.  As a result, the plate heats up, melts and forms volcanoes.  In this case the islands are classified as volcanic arcs.  As a result of this collision, along the boundary the Aleutian Trench was formed and the deepest section measures 25,663 ft!  For comparison purposes, the deepest point in the ocean is located in the Mariana’s Trench at 36,070 feet (6.8 miles)! Through the use of radioisotopic dating of basalt rocks throughout the Aleutians, geologists have concluded the formation of the island chain occurred 35 million years ago. (USGS). Today, there are 14 volcanic islands and an additional 55 smaller islands making up the island chain.

ConvergentBoundary

The Aleutian Islands – yellow line indicates subduction boundary (Courtesy of US Geologic Survey)

On the map above, the Aleutian Islands appear small. However, they extend an area of 6,821 sq mi and extend out to 1,200 miles!  In comparison, North Carolina from the westernmost point to the Outer Banks is 560 miles, half of the Aleutian Islands.  It takes roughly ten hours to drive from Murphy NC (western NC)  to the Outer Banks of North Carolina. Since this region of the North American plate and the Pacific Plate are both oceanic plates, Island Arcs are formed.  This is the same classification as the Bahamas, located southeast of Florida.

North American and Pacific Plates

Convergence of North American and Pacific Plates – Image courtesy of US Geologic Survey

 

Oceanic-OceanicPlate

Convergence of two Oceanic Plate – Image courtesy of US Geologic Survey

The image above depicts a cross section of the geological forces that shaped the Aleutian Islands.  As the two plates collide, the oceanic crust is subducted under the lithosphere further offshore thus generating the island arcs.  Unlike the west coasts of Washington, Oregon and California,  there is an oceanic/continental collision of plates resulting in the formation of volcanoes further on the continental crust, hundreds of miles inland.  Examples are Mount Rainier, Mount Hood, and Mount St. Helen’s which erupted in 1980.

Alpine Glaciers are prevalent throughout the mountainous region of Alaska. What about the Aleutians Islands? Today there are a few small alpine glaciers existing on Aleutian Islands. Alpine glacier on the Attu Island is one example, which is the western most island.

 

Personal Log 

One truth about being at sea is don’t trust the wall, floor or ceiling. Sometimes, the wall will become the floor or the ceiling will become the wall 🙂 Lately, the seas have become this ongoing amusement park ride.  Although the weather has been a bit rough, data collection continues with the ship.  The weather outside is more reflective of fall and winter back in North Carolina, though we have not seen any snow flakes.  After surfing the waves yesterday while collecting data, today the hydrographers are processing data collected over the past few days.

Yesterday was whale day!  Early afternoon, humpbacks were spotted from the port side of the ship (left side).   As the afternoon went on, humpbacks were spotted all around the Fairweather, at distances of 0.5 miles to 5 miles.  Humpbacks are considered the “Clowns of the Seas” according to many marine biologists.  Identifying whales can be tricky especially if they are distances greater than a few miles. Humpbacks are famous for breaching the water and putting on a show,  Yesterday we did not witness this behavior, however they were showing off their beautiful flukes.

Humpback whale fluke

Humpback whale fluke, photo courtesy of NOAA

 

Question of the Day:    Which whale species, when surfacing, generates a v shape blow?

Until next time, happy sailing!
Tom

2 responses to “Tom Savage: The Physical Geography of the Aleutian Islands, August 16, 2015

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