Page 383 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Earth’s Migrating Magnetic Poles
2013 150° 135° 120° 105° 90° 75° 2010
In Chapter 1, we discussed the north geo-
graphic pole—the axial pole centred
where the meridians of longitude con-
verge. This is true north and is a fixed point.
Another “north pole” also exists, this one
in association with Earth’s magnetic field. declination. Then, to calculate true The North Magnetic Pole (nMP) is the pole north from a compass reading, you toward which a compass needle points. add or subtract (depending on your Before the global Positioning System (gPS) longitude relative to the nMP) the was in widespread use, people relied on magnetic declination appropriate to the compass to find direction, making the your location.
location of this pole critical for navigation. For example, in 2014 at Vancouver, Since the location of this pole changes, the British Columbia, the declination was nMP must be periodically detected and 17° east of true north (with an annual pinpointed by magnetic surveys. change of 11∙ to the west). However, at
The deep interior of Earth—the core— Vermilion Bay in northwestern Ontario,
has a solid inner region and a fluid outer 130 km east of the Manitoba border, region. Earth’s magnetic field is principally the declination was 0° (changing 6∙ to generated by motions in the fluid mate- the east per year)—at this location, the
rial of the outer core. Like a bar magnet, nMP and true north were aligned in
the magnetic field has poles with opposite 2014.
charges. At the nMP, the pull of the mag-
netic field is directed vertically downward; Movement of the Poles During imagine this pull as an arrow pointing the past century, the nMP moved downward, intersecting Earth’s surface at 1100 km across the Canadian 0 the north and south magnetic poles. The Arctic. Presently, the nMP is moving movement of the magnetic poles results northwest toward Siberia at approxi- from changes in Earth’s magnetic field. mately 55–60 km per year. The observed
Magnetic Declination Today, a compass needle does not point to true north. The angular distance in degrees between the direction of the compass needle and
Table GN 12.1 Approximate North Magnetic Pole Coordinates, 2003 to 2015
positions for 1831–2013 are mapped in Figure gn 12.1 and listed in Table gn 12.1. Each day, the actual magnetic pole migrates in a small oval pattern around the average locations given on the map. The geological Survey of Canada (gSC) tracks the location and movement of the nMP (see geomag.nrcan.gc.ca/index-eng.php).
In 2013, the nMP was near 85.9° n by 149° W in the Canadian Arctic. Its antipode, or opposite pole, the South Magnetic Pole (SMP), lay off the coast of Wilkes Land, Antarctica. The SMP moves separately from the nMP and is
▲Figure GN 12.1 North Magnetic Pole Movement, 1831 to 2013.
geosystems now online For more about magnetic declination, go to geomag.nrcan .gc.ca/mag_fld/magdec-eng.php, Click on the “Declination calculator” on the right to determine the declination for your cur- rent location
SOUTH PACIFIC OCEAN
Year latitude
(°N) (°W)
2003 82.0
2004 82.3
2005 82.7
2006 83.9
2007 84.4
2008 84.2
2009 84.9
2010 85.0
2011 85.1
2012 85.9
2013 85.9
2014 85.9
2015 86.1
(predicted)
longitude
the line of longitude at a given loca- tion is the magnetic declination. Since the nMP is constantly on the move, knowledge of its present location is essential for determining the magnetic
ARCTIC OCEAN
2007
2001 1994
85°
Ellesmere Island
60°S
180°
165°E
112.4
113.4 presently headed northwest at just
165°W
150°E
114.4
119.9 we explore Earth’s interior in this
121.7
147.0 148.0 149.0 153.0
chapter, we discuss the chang-
2010
1950
5 km per year (Figure gn 12.2). As
135°E
ing intensity of Earth’s magnetic 124.9 field and how the field periodi- cally reverses polarity. We discuss 131.0 in later chapters the effects of the 132.6 magnetic field on animal migration 134.0 and how birds and turtles, among other animals, can read magnetic
declination.
▶Figure GN 12.2 South Magnetic Pole Movement, 1590 to 2010. [Based on Magnetic Field Models, nOAA ngDC.]
1900
1850
Ross Sea
80°
75°
2005
Victoria Island
Resolute
Baffin
125
250 KILOMETRES
Melville Island
1984
105°
90°
T
r
a
75°S
150°W
n
s
A
n
t
120°E
a
r
c
135°W
t
i
ANTARCTICA
Vostok
(RUSSIA)
0 400
South Pole
Amundsen-Scott
(U.S.)
c
M
o
105°E
u
n
t
105°W
800 KILOMETRES
now
geosystems
1962 1948
1831
1972
Island 1904
75°
1800
1700 1650 1750 1600
Ross Ice Shelf
1590
70°
a
i
n
s
90°W
90°E