The document discusses volcanoes and how they form. It explains that volcanoes form at subduction zones, where tectonic plates collide and one plate slides under another. This causes friction and melting within the Earth, and magma rises up through the crust. When it reaches the surface, it erupts as lava from a vent to form a volcano. Many volcanoes are located on the Pacific Ring of Fire, which is a horseshoe-shaped area in the Pacific Ocean known for seismic activity and volcanoes. Within this area are several subduction zones, including those responsible for the over 20 active volcanoes located in the Philippines.

1. VOLCANOES AND
THE INTERIOR OF
THE EARTH

2. FORMATION OF VOLCANOES
A volcano is a vent in the Earth's crust
(outermost layer of the Earth; from which
materials such as molten rock and steam
are ejected. There are about 1,500 active
volcanoes in the world today.

4. The Philippine Institute of Volcanology and Seismology
(PHIVOLCS),the country's government agency that deals with
volcanic activities and earthquakes,has listed about 23 active
volcanoes, 26 potentially active volcanoes, and about more than
300 named and unnamed inactive volcanoes found in the
different parts of the Philippine archipelago
The Philippines is considered one of the countries with many
volcanoes and gigantic volcanic explosions. This is because the
Philippines sits on the Pacific Ring of Fire, a region of high
seismic and volcanic activities that surrounds the basin of the
Pacific Ocean (fig 10.3). The Philippine is surrounded by plates
(slabs of archipelago solid rocks) where volcanoes usually form.

6. Pacific Ring of Fire
The Pacific Ring of Fire, often simply known as the
Ring of Fire, is not even circular. Rather, it is a huge,
horseshoe-shaped path along the Pacific Ocean
known for creating different sorts of big seismic
events, such as major earthquakes and fiery
volcanoes.

7. HOW BIG IS THE RING OF FIRE?
The Pacific Ring of Fire is 25,000 miles long and
encompasses mountains, earthquake epicenters, and
volcanoes around much of the rim of the Pacific
Ocean, according to the National Oceanic and
Atmospheric Administration (NOAA). It accounts for a
large swath of the Earth’s total land and water
surfaces.

8. WHERE IS THE RING OF FIRE LOCATED?
The Ring of Fire is an arc of mountains, active
volcanoes, and oceanic trenches that stretch from
New Zealand northward along the eastern edge of
Asia, then east across the Aleutian Islands of Alaska,
and then south along the western coasts of North
America, including California, and South America.

9. How do Volcanoes
Form?

10. 1. SUBDUCTION
Volcanoes are formed in various size sand shapes
Cone-shaped volcanoes are the most common ones.
Some volcanoes are only a long crack in the crust,
while others resemble high mountains, which are
formed due to frequent volcanic eruptions. According to
the theory of plate tectonics, the crust has many rigid
plates on Earth's mantle that are floating on the Earth’s
mantle.

11. The pressure created by the convection currents in the mantle
causes the movement of these plates When pressure becomes
intense, the plates move horizontally either toward each other or
away from each other.

13. When two plates collide, one of the plates goes beneath other. This
process is called subduction. During the process, a subduction zone,
the boundary where two tectonic plates collide, is formed. Along the
Pacific Ring of Fire are several subduction zones. As a subducting plate
is forced deeper and deeper underground, it causes friction in the
Earth's crust. The pressure resulting from the friction causes the
underlying rocks to melt and makes the magma rise through gaps in the
Earth's crust. A gap is formed when two plates move away from each
other. The magma forces its way to the surface and then becomes a
hot, reddish- orange lava as it blasts out of the crack or hole on the
Earth's surface. This activity is not visible if it occurs in the seabed.If a
volcano in an ocean or sea erupts, the volcanic materials solidify and
may rise above the water surface, forming an island.

15. Examples of such
islands are the
Didicas volcanic
island in Cagayan,
Philippines and the
Kavachi submarine
island in Solomon
Islands

16. 1. HOT SPOTS
Hot spots are the center points of the plates. As already
mentioned, the plates float on the mantle, from which
magma originates. Magma, which rises through the gaps,
becomes lava when it shoots out of the Earth's crust. Lava
and other volcanic materials become hard when they cool
down and form a volcanic mountain. A volcano is a mountain
that has formed from lava and other materials.

18. PARTS OF VOLCANO
The major parts include the flanks, summit, crater vent, conduit, and
secondary or branch pipes, and the magma chamber or reservoir.

19. The flanks, which are the sides of a volcano, extend
to the summit.
The summit is the apex or the highest point of a
volcano. It usually contains the crater, which is the
mouth of a volcano. Sometimes, a crater is
confused with a caldera, which is a volcanic feature
that resembles a cooking pot or cauldron.

20. The summit also contains vent, which is an
opening that allows the lava to be ejected from
the volcano. The vent extends to the conduit, the
pipe or the channel that conveys the magma. The
secondary pipes or branch pipes originate from
the conduit. Magma comes from e large
underground pool of molten rocks called the
magma chamber or magma reservoir.

21. ● Active volcanoes are volcanoes that
● have erupted within the last 600 years.
● These types of volcanoes are expected to
● erupt in the future.
● SA categorized Lq the PHIVOLCS there
● are 23 active volcanoes in the country. Some
● volcanoes that erupt more frequently than
● others are Mayon Volcano, Taal Volcano,
● Kanlaon Volcano, and Bulusan Volcano.