in 1621. However, the Poles and the
Swedes let the city govern itself. Russia
took over Riga in the early 1700s.
In 1918 Latvia became an independent
country with Riga as its capital. But the
Soviet Union took control of Latvia in
1940. In 1991 Latvia broke away from
the Soviet Union and became independent
again. Riga remained its capital.
..More to explore
Latvia
Ring of Fire
A chain of volcanoes surrounds the
Pacific Ocean. Because the volcanoes
frequently erupt in fiery explosions, the
region is known as the ring of fire. Many
earthquakes occur in the region as well.
The chain passes along the west coast of
North and South America. It runs along
the Aleutian Islands and the islands of
East and Southeast Asia. Then it extends
east and south to New Zealand.
The ring of fire surrounds the edges of
the giant Pacific Plate. A plate is a section
of the rocky outer layer of Earth.
Earth’s plates move at different rates and
in different directions. As the Pacific
Plate and the plates around it grind into
each other, they cause earthquakes and
volcanoes.
..More to explore
Earthquake • Volcano
Rio de Janeiro
Population
(2007
estimate), city,
6,093,500;
urban area,
11,563,302
Rio de Janeiro is a large city in Brazil, a
country in South America. It is the second
largest city in the country, after Sao
Paulo. The city lies on the Atlantic
Ocean. It is often called Rio for short.
Tourists flock to Rio for its beautiful
beaches and for a yearly festival called
Carnival. The city celebrates Carnival
for four days before the Christian
season of Lent begins. Lively parades
and parties last day and night. People in
colorful costumes sing and dance in
Rio’s streets.
Places of Interest
A large statue of Jesus called Christ the
Redeemer overlooks Rio de Janeiro. It
66 Ring of Fire BRITANNICA STUDENT ENCYCLOPEDIA
stands on Mount Corcovado. A rock
called Sugar Loaf is another major landmark.
The rock offers great views of
Rio’s beaches below. Two of its bestknown
beaches are called Copacabana
and Ipanema.
Economy
Tourism is a major part of Rio de
Janeiro’s economy. Banking, trade, and
other services are also important. The city
is one of Brazil’s main manufacturing
centers. Factories in Rio make clothing,
medicines, metal products, and processed
foods. The city is also a major port.
History
Portugal took control of Brazil in the
1500s. Many American Indians already
lived in the Rio area. Portuguese sailors
entered the area’s harbor in January
1502. They thought it was the mouth of
a river. Because of this they named the
site Rio de Janeiro, which means “river
of January.” Portuguese settlers began
moving there in the 1560s.
In the 1700s the Portuguese used Rio as
a port to ship out gold and diamonds.
In 1763 they made it the capital of their
colony of Brazil. The city grew greatly.
Brazil became an independent country
in 1822. Rio was its capital. In 1960 the
capital was moved to the city of Brasilia.
However, Rio de Janeiro remained
important to Brazil’s economy.
#More to explore
Brasilia • Brazil • Sao Paulo
River
A river is a large, natural stream of water
that flows over land. Rivers shape the
land by carving out canyons and other
valleys. Humans have used rivers in
many ways. Many ancient civilizations
grew up near rivers.
River Courses
A river begins as a tiny trickle of water
on high ground. The water may come
from rainfall, from melting snow or ice,
or from underground. The trickle com-
Rio de Janeiro lies on a bay of the Atlantic
Ocean. A towering rock called Sugar Loaf
stands at the entrance of the bay.
A boat pushes barges on the Mississippi
River.
BRITANNICA STUDENT ENCYCLOPEDIA River 67
bines with other trickles as it flows
downhill. It may be called a stream, a
brook, or a creek.
Eventually the creek grows into a river.
In its upper course the river flows rapidly.
It cuts through the land and picks
up soil and gravel. In its middle course
the river flows down gentler slopes. It
gets larger and slower. Soil, gravel, and
sand begin to sink to the bottom.
In its lower course the river flows even
more slowly. It drops still more solid
material. Some material is carried all the
way to the mouth—the place where the
river enters the sea. This material may
build up to form a piece of land called a
delta.
River Systems
A river receives water from the smaller
streams that flow into it. These streams
are called tributaries. A river and its
tributaries make up a river system. The
area that a river system covers is called a
basin. Rivers that are the same length
may have basins of different sizes. The
Amazon River is slightly shorter than
the Nile River, but the Amazon has a
basin more than twice as large.
Importance to Humans
Humans drink river water. They catch
fish from rivers. They also use river water
to grow crops. They often do this by
digging ditches that carry water to farm
fields. This practice is called irrigation.
Before modern times, people often
traveled on rivers. Large riverboats called
barges still carry grain, coal, and minerals.
Flooding creates problems for people
who live near rivers. People have built
dams across many rivers to control
