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magma. These black to reddish-brown fragments are generally found in the size range
of lapilli and resemble cinders and clinkers produced by furnaces used to smelt iron.
When magmas with intermediate (andesitic) or felsic (rhyolitic) compositions erupt
explosively, they emit ash and the vesicular rock pumice. Pumice is usually lighter in
color and less dense than scoria.

Task 2. Look at Figures 7.2. Try to define the volcanic rocks A and B. What
do you know about them?

Task 3. Look at Figure 7.3. It shows pyroclastic materials. A. Volcanic ash
and small pumice fragments (lapilli) that erupted from Mount St. Helens in 1980.
Inset photo is an image obtained using a scanning electron microscope (SEM). This
vesicular ash particle exhibits a glassy texture and is roughly the diameter of a
human hair. B. Volcanic block. Volcanic blocks are solid fragments that were
ejected from a volcano during an explosive eruption. C. These basaltic bombs were
erupted by Hawaii’s Mauna Kea volcano. Volcanic bombs are blobs of lava that
are ejected while still molten and often acquire rounded, aerodynamic shapes as
they travel through the air. Describe pyroclastic materials shown in Figure 7.3.

Test yourself

Task 1. Tell whether the sentences are true or false. Correct the false ones.
1. A path of the gas-rich magma moving up through a fissure is usually localized into
a pipe.
2. A surface opening in the volcanic activity is called a vent.
3. A cone-shaped structure is usually called a crater.
4. Craters can also form when the summit area of a volcano collapses following an
eruption.
5. Cinder cones are produced by the accumulation of fluid basaltic lavas and exhibit
the shape of a broad, slightly domed structure that resembles a warrior’s shield.
6. Examples of the composite cones include the Canary Islands, the Hawaiian
Islands, the Galapagos, and Easter Island.
7. Cinder cones are composed mostly of loose pyroclastic material.
8. The Andes in South America and the Cascade Range of the western United States
and Canada are the examples of shield volcanoes.
9. Two of the most perfect cones—Mount Mayon in the Philippines and Fujiyama in
Japan—exhibit the classic form of a composite cone.
10. The composition of volcanic gases is not that important because they do not
contribute to our planet’s atmosphere.
11. Pyroclastic materials range in size from very fine dust and sand-sized volcanic
ash to pieces that weigh several tons.
12. When the hot ash falls, the glassy shards often fuse to form a rock called lapilli.
13. Scoria is the name of vesicular ejecta - a product of basaltic magma.
14. When magmas with andesitic or felsic compositions erupt explosively, they emit
ash and pumice.

Task 2. Fill in the gaps with the suitable words and word-combinations.

pyroclastic material, pahoehoe, gases, lapilli, aa
The materials associated with a volcanic eruption include (1) lava flows ( …
flows, which resemble twisted braids; and … flows, consisting of rough, jagged blocks;
both form from basaltic lavas); (2) … (primarily water vapor); and (3) … (pulverized

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