Page 30 - (DK Eyewitness) Travel Guide 2017 - Alaska

28  INTRODUCING ALASK A

Volcanoes and Earthquakes
ARCTIC OCEAN
Alaska lies on the geologically active Pacific Ring of RUSSIA
Fire, where tectonic shifts can result in earth quakes ALASKA CANADA
and volcanic eruptions. One of the earth’s tectonic Anchorage
plates is sliding under another, causing major geo- Aleutian Islands Juneau
Bering Sea
logical changes. The entire southern Alaskan region is
geologically dynamic; it is the site of about 8 percent Gulf of Alaska
of all the world’s earth quakes and boasts dozens of PACIFIC OCEAN
active volcanoes. The second strongest earthquake in
recorded history struck Southcentral Alaska in 1964, Locator map
and in 1912, Novarupta exploded in what was the Aleutian Megathrust
second most powerful volcanic eruption ever recorded. Subduction zone
Great Sitkin (1987),
a 5,742-ft (1,740-m)
volcano, is a vent
inside the cal dera
of an older shield
volcano on the
well-glaciated Great
Sitkin Island, which is
covered in a layer of
dark pumice 20 ft Mount Cleveland (2010), a symmetrical 5,675-ft
(6 m) thick. (1,730-m) cone on Chuginadak Island, is one of the
Aleutians’ most active vol canoes. This dramatic
peak is a prominent fea ture of the beautiful
Islands of Four Mountains. Amak (1796)
Little Bogoslof Fischer
Sitkin Makushin
Kiska (1992) (1995) Akutan
(1962) Bearing Sea (1992)
Okmok
Tanaga Kanaga Carlisle (1987) (2008)
(1914) (1996)
Korovin Amukta Vsevidof Unalaska
(2006) (1997) (1957)
Fox
Rat Islands
Atka Islands
The Aleutian Adak Nikolski
Megathrust is a very Andreanof Islands Seguam Yunaska Kagamil
active fault line that Gareloi (1993) (1937) (1929)
is responsible for the (1996)
numerous earthquakes
in southern Alaska. Aleutian Trench
Tectonic Activity North American Volcanic Aleutian Pacific
The distinctive chain of islands and peaks (continental) plate zone Trench (oceanic) plate
that makes up the Aleutian Islands is the
result of plate tectonics – the movement
of the interlocking plates of the earth’s crust
that ride on the molten material (magma)
in the mantle. At the subduction zone, the
oceanic Pacific plate is being forced under
the continental North American plate, creating
the Aleutian Trench. North of this zone, fractures
in the continental plate allow magma from
below to migrate upward. When the pressure
increases, the magma bursts through the crust Model of a subduction zone
in dramatic volcanic activity. and trench

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