People in the Mountains - Mountain Geography: Physical and Human Dimensions - page 496

over- and bypasses, and long tunnels (e.g., the 8-km Mt. Blanc Tunnel between France
and Italy), all common on superhighways in the Alps, North American Cordillera, and,
increasingly, in the Himalaya of India and southwestern China.
Many of the influences, constraints, and benefits produced by mountain topography
are visible through their impact on other environmental elements. For example, with
gain in altitude, atmospheric pressure and air temperature decrease; each has direct
impacts on people. The orientation of mountain ridges and valleys controls exposure
to sunlight, thereby affecting local energy balance. Topography influences water forms,
sources, and movement. Likewise, it impacts airflow locally and atmospheric circulation
regionally and globally, all of which influence the geography of precipitation. As dis-
cussed in Chapter 7, the gradations seen in the mountain environment with gain in alti-
tude are very evident in the vegetation patterns so that distinct altitude-based vegeta-
tion or ecological zones are evident. Similar topographic zonation is evident in agricul-
tural and other land uses and, thereby, the livelihoods of people.
Atmospheric Pressure
Atmospheric pressure declines with increased altitude, and therefore the oxygen avail-
able to humans and other aerobic life forms is also reduced. This produces short-term
physiological changes and longer-term physiological adjustments and adaptations in
people. Long-term high mountain residents have more hemoglobin in their blood, larger
lung and heart volumes, shorter extremities, and more bone marrow. Fertility, growth
and maturation, and morbidity and mortality in populations of mountain people are af-
fected. Many essential human activities based on combustion—for example food prepar-
ation and operation of combustion-powered machinery—are also affected. Human oxy-
gen deficit, or hypoxia, is not unique to altitudinal air pressure depletion, but is a con-
dition found at all altitudes among people who are physiologically challenged in their
oxygen uptake. In the mountains, it affects all people, whether permanent or semiper-
manent residents or transients. Our understanding of it comes from a very long scientif-
ic interest and, more recently, from intensive research on high-altitude mountaineers
and permanent residents (Baker 1978; Houston 1998; West and Readhead 2004).
The most obvious and immediate effect on people as they gain altitude is shortness of
breath. Other short-term effects may include dizziness, headaches, nausea, nosebleeds,
and tiredness. People display altitude-based hypoxia symptoms differently. Some begin
to feel these effects at altitudes under 1,500 m, while others do not experience ill effects
even at 4,000 m. People who live permanently or for extended periods at high altitude
display physiological adaptations through acclimatization that reduce hypoxia. Moun-
tain climbers, for example, take extra time to ascend to higher altitudes so that their
bodies adjust to reduced oxygen. Some climbers have briefly reached altitudes of over
8,000 m without supplemental oxygen. Acclimatization involves an increase in the num-
ber of red (oxygen-carrying) cells in the bloodstream, an increase in lung capacity to in-
crease oxygen absorption, and an increase in the heart's ability to pump blood through
the bloodstream. Understanding of altitude-driven hypoxia has increased over the past
200 years, as more people travel to the mountains on a short-term basis for work, recre-
ation, and tourism (West 2004). Up to an altitude of about 5,000 m, with proper accli-
matization, nourishment, and hydration most healthy people can maintain normal body