A subduction zone, composed of the deep Aleutian Trench coupled with a landward line of volcanoes, creates a series of offshore islands (the Aleutians) as well as a line of volcanoes along the edge of the continent (the Aleutian Range on the Alaska Peninsula).

In addition to subduction, two other major tectonic processes have helped shape this area of the Alaskan continental margin: terrane migration and rotation of the mainland. The terranes of previously separated crustal blocks have migrated due to sea-floor spreading and some believe southwestern Alaska has rotated counterclockwise in response to collision of the north-west migrating collection of terranes with Siberia.

The rocks that make-up the Alaska Peninsula are primarily arc-related, volcanic and plutonic rocks and shallow marine and continental sedimentary rocks that range from Paleozoic to Holocene in age. Figures A and B show the positions of the Peninsular, Chugach, and Prince William trerranes in relation to the modern coastline of Alaska. The Peninsular terrane is believed to have stopped its migration northward between 65 to 55 mya. At this time convergence occurred and one plate was subducted beneath the other. The Chugach terrane which is composed of turbidites, submarine basalt flows and dikes formed an accretionary wedge just above the subduction zone. At this convergence zone the Border Ranges Fault is evidence for a megathrust. Between 60 and 43 mya a 30 to50 degree counterclockwise rotation of southern Alaska occurred. This signifies the beginning of the modern Aleutian subduction zone and accretionary complex. This northwesterly shift was the impetus for volcanism on the Alaska Peninsula and inner Shumagin Islands . The partial melting of the mantle wedge located above the subducting plate lead to the growth of this volcanic island arc.

Traveling from Unga Island to the Bering Sea we crossed the archipelago at False Pass near Unimk Island. At the time, I was interested in spotting and photographing pelagic birds, however it was hard to ignore the numerous smoking volcanoes. Click on the image to see a letter from John Muir to his family describing the Aleutian landscape. John Muir was America's most famous and infuential naturalist and conservationist.

The volcanoes produced in this area of Alaska are typically stratovolcanoes. These volcanoes tend to have a conical shape with a steep summit and gradually sloping flanks. The form is the due to the nature of the viscous lavas and pyroclastic ejecta. Coarse fragments tend to accumulate near the summit crater which accounts for the steep slopes of the summit, whereas the finer ejecta are deposited as a thin layer over a large area. This will flatten the flank of the cone. Also, the cones broad base can be attributed to the early stages of growth when lava tends to be more abundant and flow greater distances. Overtime, the flows from the vent will become shorter adding strength to the summit area.

These are remnants of a 20 million year old Metasequoia forest that was buried by a volcanic mudflow. The trees are petrified by a process known as permineralization. This occurs when groundwater mixes with dissolved silica derived from the volcanic ash and begins to fill in the woody tissues pores. Over millions of years, the wood becomes encased in quartz crystals. On the northwest side of the island numerous Sequoia logs and stumps up to 50 ft long and 5 ft diameter can be found along four miles of the shoreline.

	The two NE trending zones are based on physiographic linements, zones of silicification, quartz veins, and local faulting. The intense mineralization occured during Popof volcanism in the late Oligocene.

	From 1886 to 1912 two gold mines were operated near the head of Delarof Bay on the south side of the island . It was estimated that both mines yielded approximately $3 million in gold and secondary silver. Since the early 1900s there has been no production from Unga claims. However, preliminary exploratory drilling has been conducted. If you look to the right of the generator there are hundreds of cores. The ground is littered with cores that have been discarded and vandalized. Photo by A. Schmidt
	View across Baralof Bay from Squaw Harbor. The white structure on the right side of the photo is the shack pictured above. It marks the start of the Shumagin trend that occupies a fault zone that strikes N60E and dips 80-85SE.
	The dome in the background is composed of crystal-rich, porphyritic Zachary Bay lava flows (Tpz) mainly consisting of high-silica andesite from the Tertiary. The summit is over 2000 ft, it is one of the highest points on Unga. Most of the photos on this website were taken from the summit of this dome. The foreground is primarily undifferentiated Popof volcanic rocks (Tpu) from the late Eocene to Oligocene. Mainly lava flows and flow breccias of andesite composition. The shore line is chiefly unconsolidated deposits (Qs), sand and gravel on beaches. Photo by A. Schmidt
	This is a photo from the summit of the previous photo looking to the northwest. The two summits are Zachary Bay lava flows (Tpz) consisting of andesite. Photo by A. Schmidt
	This is also a photo from the 2000 ft summit. The waterbody is Baralof Bay and the small dome feature in the center is an undifferentiated dome from the Oligocene (Tpdu). Notice the breccia along the ridge top. Photo by A. Schmidt
	Same view as previous picture, photo was taken half-way down the ridge. Hiking back to Squaw Harbor, we decided to follow the intermittent streams which were full of pink salmon. Photo by A. Schmidt
	View of Dearof Bay from the shores of Unga. The sea arch in the distance is known as Elephant Rock. This landform is the result of incoming waves that focus on the headland point and onto its flanks. The waves erode sea caves into the headland that eventually meet in the middle. In a few centuries the arch will collapse and form a sea stack or tombolo. Photo by A. Schmidt.

After graduating I decided to explore the west coast for a month. I purchased an open amtrak ticket and set out on an adventure. Two montsh later I was hiking on Unga.

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