ESS 101 B Lab 4 Quiz Volcanoes Plutons Igneous Rocks
Actual Exam 2026/2027 – Complete Solved with Detailed
Rationales | 100% Verified | Pass Guaranteed – A+ Graded
Section A: Igneous Rock Formation & Magma vs. Lava (10 Questions)
Q1: A geology student observes molten rock flowing from a volcanic vent on the surface
of Hawaii. This material is correctly classified as:
A. Magma
B. Lava [CORRECT]
C. Pyroclastic debris
D. Plutonic rock
Correct Answer: B
Rationale: Lava is defined as magma that has reached Earth's surface. Magma remains
underground. Pyroclastic debris refers to fragmented volcanic material ejected during
explosive eruptions, and plutonic rocks form from magma that cools and solidifies
beneath the surface.
Q2: Approximately what fraction of Earth's crust is composed of igneous rocks?
A. 1/5
B. 2/5
,C. 4/5 [CORRECT]
D. 3/4
Correct Answer: C
Rationale: Approximately 4/5 (80%) of Earth's crust is composed of igneous rocks,
making them the most abundant rock type in the crust by volume. Sedimentary and
metamorphic rocks compose the remaining fraction.
Q3: The first rocks to form on Earth approximately 4 billion years ago were:
A. Sedimentary rocks formed from ancient oceans
B. Metamorphic rocks from early tectonic activity
C. Igneous rocks from cooling magma and lava [CORRECT]
D. Chemical precipitates from the primordial atmosphere
Correct Answer: C
Rationale: The first rocks to form on Earth were igneous rocks, created from the cooling
and solidification of the planet's initial molten magma and lava. Sedimentary and
metamorphic rocks require pre-existing rocks and specific processes that developed
later in Earth's history.
Q4: A geologist discovers a rock body that formed from magma cooling slowly beneath
an ancient mountain range. This rock body is classified as:
A. Extrusive igneous rock
,B. Intrusive (plutonic) igneous rock [CORRECT]
C. Volcanic glass
D. Pyroclastic deposit
Correct Answer: B
Rationale: Intrusive (plutonic) igneous rocks form when magma cools and solidifies
beneath Earth's surface. Extrusive igneous rocks form from lava at the surface. Volcanic
glass and pyroclastic deposits are specific types of extrusive materials.
Q5: During a field expedition, a student collects a sample from a lava flow that cooled
rapidly in contact with air. This sample most likely represents:
A. A plutonic intrusion
B. An extrusive igneous rock [CORRECT]
C. A metamorphic aureole
D. A sedimentary bed
Correct Answer: B
Rationale: A lava flow that cooled at Earth's surface produces an extrusive igneous rock.
The rapid cooling at the surface is characteristic of extrusive environments. Plutonic
intrusions cool slowly underground, metamorphic aureoles form from contact
metamorphism, and sedimentary beds form from deposition and lithification.
Q6: Which of the following best describes the process by which all igneous rocks form?
, A. Compaction and cementation of sediments
B. Cooling and solidification of magma or lava [CORRECT]
C. Heat and pressure applied to existing rocks
D. Chemical precipitation from hydrothermal fluids
Correct Answer: B
Rationale: All igneous rocks form through the cooling and solidification of magma
(underground) or lava (at the surface). Compaction and cementation form sedimentary
rocks; heat and pressure form metamorphic rocks; chemical precipitation can form
some sedimentary or hydrothermal deposits but not igneous rocks.
Q7: A volcanic eruption produces fluid basaltic material that flows across the landscape
and eventually hardens. The resulting rock is:
A. Granite
B. Rhyolite
C. Basalt [CORRECT]
D. Gabbro
Correct Answer: C
Rationale: Basalt is the fine-grained (aphanitic) extrusive equivalent of gabbro. It forms
from mafic lava that cools rapidly at the surface. Granite and gabbro are intrusive rocks,
and rhyolite is the extrusive equivalent of granite (felsic, not mafic).
Actual Exam 2026/2027 – Complete Solved with Detailed
Rationales | 100% Verified | Pass Guaranteed – A+ Graded
Section A: Igneous Rock Formation & Magma vs. Lava (10 Questions)
Q1: A geology student observes molten rock flowing from a volcanic vent on the surface
of Hawaii. This material is correctly classified as:
A. Magma
B. Lava [CORRECT]
C. Pyroclastic debris
D. Plutonic rock
Correct Answer: B
Rationale: Lava is defined as magma that has reached Earth's surface. Magma remains
underground. Pyroclastic debris refers to fragmented volcanic material ejected during
explosive eruptions, and plutonic rocks form from magma that cools and solidifies
beneath the surface.
Q2: Approximately what fraction of Earth's crust is composed of igneous rocks?
A. 1/5
B. 2/5
,C. 4/5 [CORRECT]
D. 3/4
Correct Answer: C
Rationale: Approximately 4/5 (80%) of Earth's crust is composed of igneous rocks,
making them the most abundant rock type in the crust by volume. Sedimentary and
metamorphic rocks compose the remaining fraction.
Q3: The first rocks to form on Earth approximately 4 billion years ago were:
A. Sedimentary rocks formed from ancient oceans
B. Metamorphic rocks from early tectonic activity
C. Igneous rocks from cooling magma and lava [CORRECT]
D. Chemical precipitates from the primordial atmosphere
Correct Answer: C
Rationale: The first rocks to form on Earth were igneous rocks, created from the cooling
and solidification of the planet's initial molten magma and lava. Sedimentary and
metamorphic rocks require pre-existing rocks and specific processes that developed
later in Earth's history.
Q4: A geologist discovers a rock body that formed from magma cooling slowly beneath
an ancient mountain range. This rock body is classified as:
A. Extrusive igneous rock
,B. Intrusive (plutonic) igneous rock [CORRECT]
C. Volcanic glass
D. Pyroclastic deposit
Correct Answer: B
Rationale: Intrusive (plutonic) igneous rocks form when magma cools and solidifies
beneath Earth's surface. Extrusive igneous rocks form from lava at the surface. Volcanic
glass and pyroclastic deposits are specific types of extrusive materials.
Q5: During a field expedition, a student collects a sample from a lava flow that cooled
rapidly in contact with air. This sample most likely represents:
A. A plutonic intrusion
B. An extrusive igneous rock [CORRECT]
C. A metamorphic aureole
D. A sedimentary bed
Correct Answer: B
Rationale: A lava flow that cooled at Earth's surface produces an extrusive igneous rock.
The rapid cooling at the surface is characteristic of extrusive environments. Plutonic
intrusions cool slowly underground, metamorphic aureoles form from contact
metamorphism, and sedimentary beds form from deposition and lithification.
Q6: Which of the following best describes the process by which all igneous rocks form?
, A. Compaction and cementation of sediments
B. Cooling and solidification of magma or lava [CORRECT]
C. Heat and pressure applied to existing rocks
D. Chemical precipitation from hydrothermal fluids
Correct Answer: B
Rationale: All igneous rocks form through the cooling and solidification of magma
(underground) or lava (at the surface). Compaction and cementation form sedimentary
rocks; heat and pressure form metamorphic rocks; chemical precipitation can form
some sedimentary or hydrothermal deposits but not igneous rocks.
Q7: A volcanic eruption produces fluid basaltic material that flows across the landscape
and eventually hardens. The resulting rock is:
A. Granite
B. Rhyolite
C. Basalt [CORRECT]
D. Gabbro
Correct Answer: C
Rationale: Basalt is the fine-grained (aphanitic) extrusive equivalent of gabbro. It forms
from mafic lava that cools rapidly at the surface. Granite and gabbro are intrusive rocks,
and rhyolite is the extrusive equivalent of granite (felsic, not mafic).
