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Unit 2: Geotectonics - Practice Quiz

GEO101 — Geomorphology 60 Questions
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1 What does the term isostasy describe?

isostasy Easy
A. The heating of rocks by sunlight
B. The rotation of Earth around the Sun
C. The balance between Earth's crust and mantle
D. The movement of ocean currents

2 Which material generally forms the buoyant crustal block in the concept of isostasy?

isostasy Easy
A. Molten outer-core metal
B. Solid inner-core iron
C. Less-dense continental crust
D. Dense oceanic water

3 What usually happens to land when a large ice sheet melts?

isostasy Easy
A. The land rises upward
B. The land sinks downward
C. The land becomes volcanic
D. The land moves eastward

4 Which feature commonly has a deep crustal root because of isostasy?

isostasy Easy
A. A shallow ocean beach
B. A high mountain range
C. A flat desert plain
D. A narrow river channel

5 Isostatic adjustment mainly results from changes in:

isostasy Easy
A. The speed of sunlight
B. The color of minerals
C. The salinity of rivers
D. The weight of the crust

6 Which process can cause the crust to sink because of added surface weight?

isostasy Easy
A. Mountain erosion
B. Sediment accumulation
C. Sea-level evaporation
D. Ice-sheet melting

7 Who is most closely associated with the continental drift hypothesis?

continental drift Easy
A. Isaac Newton
B. Alfred Wegener
C. James Hutton
D. Charles Darwin

8 What was Pangaea?

continental drift Easy
A. A volcanic island
B. A supercontinent
C. A type of mineral
D. A deep ocean trench

9 Which observation supports the idea of continental drift?

continental drift Easy
A. Different lengths of day
B. Daily movement of ocean waves
C. Changing phases of the Moon
D. Matching coastlines across oceans

10 Which fossil was found on continents now separated by oceans and helped support continental drift?

continental drift Easy
A. Mesosaurus
B. Ammonite
C. Trilobite
D. Tyrannosaurus

11 What does continental drift refer to?

continental drift Easy
A. The daily shifting of coastlines
B. The sinking of all continents yearly
C. The growth of continents from clouds
D. The movement of continents over time

12 Why was Wegener's original continental drift hypothesis initially criticized?

continental drift Easy
A. It used no fossil evidence
B. It denied that continents existed
C. It lacked a convincing mechanism
D. It claimed oceans never changed

13 Which evidence shows that matching rock types occur on continents now far apart?

continental drift Easy
A. Oceanic evaporation
B. Geological continuity
C. Atmospheric pressure
D. Solar radiation

14 What is a tectonic plate?

plate tectonics Easy
A. A narrow belt of river sediment
B. A rigid piece of Earth's lithosphere
C. A layer of liquid ocean water
D. A cloud of volcanic gases

15 The lithosphere includes the crust and the:

plate tectonics Easy
A. Uppermost mantle
B. Liquid outer core
C. Lowest ocean water
D. Entire inner core

16 What is a divergent plate boundary?

plate tectonics Easy
A. A boundary where plates always collide
B. A boundary where plates stop moving
C. A boundary where plates move apart
D. A boundary where plates become continents

17 What is a convergent plate boundary?

plate tectonics Easy
A. A boundary where plates move apart
B. A boundary formed by river erosion
C. A boundary where plates move together
D. A boundary without crustal movement

18 What type of plate boundary is associated with plates sliding horizontally past one another?

plate tectonics Easy
A. Subduction boundary
B. Divergent boundary
C. Convergent boundary
D. Transform boundary

19 What is subduction?

plate tectonics Easy
A. The breaking of a continent into islands
B. The rising of magma at a ridge
C. The widening of a river valley
D. The sinking of one plate beneath another

20 New oceanic crust is commonly formed at:

plate tectonics Easy
A. Continental shields
B. Mid-ocean ridges
C. Transform faults
D. Deep ocean trenches

21 According to the Airy model of isostasy, why do high mountain ranges generally have deep crustal roots?

isostasy Medium
A. Their crust is thicker but has nearly uniform density
B. Their surface rocks exert no gravitational force
C. Their crust is thinner but has much greater density
D. Their mantle is cooler and completely rigid

22 A large ice sheet melts rapidly from a continental region. What long-term crustal response is most likely?

isostasy Medium
A. The crust moves horizontally toward the former ice center
B. The crust rises as mantle material flows beneath it
C. The crust sinks as mantle material moves away
D. The crust remains fixed because unloading is temporary

23 Under the Pratt model, two neighboring crustal columns reach different elevations but extend to the same compensation depth. The higher column should have:

isostasy Medium
A. Lower average density than the lower column
B. A thinner crust than the lower column
C. Greater average density than the lower column
D. A deeper root than the lower column

24 If erosion removes a large mass of rock from a mountain range, which combination of responses is most consistent with isostatic adjustment?

isostasy Medium
A. Horizontal drift of the range and crustal thinning
B. Uplift of the range and downward erosion of its root
C. Subsidence of the range and growth of its root
D. Volcanic burial of the range and mantle cooling

25 A broad river delta receives a thick accumulation of sediment over thousands of years. What is the most likely isostatic effect?

isostasy Medium
A. The crust rises because sediment is less dense than mantle
B. The crust remains level because deposition occurs gradually
C. The crust subsides beneath the added sediment load
D. The crust spreads apart to eliminate the added mass

26 A mountain range shows a negative Bouguer gravity anomaly. Which interpretation is most consistent with Airy isostasy?

isostasy Medium
A. The mountains lack any subsurface compensation
B. A shallow oceanic slab underlies the mountains
C. A dense mantle intrusion lies beneath the mountains
D. A low-density crustal root lies beneath the mountains

27 Identical fossils of a freshwater reptile are found in eastern South America and western Africa. Why does this support continental drift?

continental drift Medium
A. The fossils formed independently in identical environments
B. The continents were once connected across the present ocean
C. The Atlantic Ocean was once entirely freshwater
D. The reptile regularly migrated across the deep Atlantic

28 Glacial deposits of similar age occur in India, southern Africa, Australia, and Antarctica. How are they best explained by continental drift?

continental drift Medium
A. The landmasses were grouped near the South Pole
B. Global sea level froze at the same latitude
C. The equator shifted across all four landmasses
D. Each landmass experienced unrelated alpine glaciation

29 Which observation provides stronger evidence for continental drift than the visual fit of modern coastlines alone?

continental drift Medium
A. Equal river lengths on neighboring continents
B. Comparable population densities in coastal regions
C. Similar present-day rainfall on opposite ocean shores
D. Matching rock belts and fossils across continental margins

30 Coal beds are discovered in Antarctica. What paleogeographic conclusion is most consistent with continental drift?

continental drift Medium
A. Ocean currents transported the coal from Australia
B. Antarctica has always remained at the South Pole
C. Coal commonly forms beneath permanent ice sheets
D. Antarctica once occupied a warmer climatic zone

31 Why did many geologists initially reject Alfred Wegener's continental drift hypothesis despite its supporting evidence?

continental drift Medium
A. He lacked a convincing mechanism for continental motion
B. He denied that continents contained sedimentary rocks
C. He proposed that Earth had no ocean basins
D. He rejected fossil evidence from southern continents

32 When South America and Africa are reconstructed before the opening of the Atlantic, which boundaries produce the best geological fit?

continental drift Medium
A. The edges of their continental shelves
B. The outer limits of their ocean trenches
C. Their present-day river drainage divides
D. Their modern political coastlines

33 Ocean-floor rocks become progressively older with increasing distance from a mid-ocean ridge. Which process best explains this pattern?

plate tectonics Medium
A. New oceanic crust forms at the ridge and spreads outward
B. Sediments push the seafloor away from continental margins
C. Oceanic crust forms at trenches and spreads toward ridges
D. Old continental crust melts at the ridge and moves inward

34 Oceanic crust located from a mid-ocean ridge is old. Assuming a constant rate, what is the half-spreading rate?

plate tectonics Medium
A.
B.
C.
D.

35 Earthquake foci become progressively deeper inland from an ocean trench. What tectonic setting does this pattern indicate?

plate tectonics Medium
A. Two continental plates are separating at a rift
B. A mantle plume is lifting the center of a plate
C. Two plates are sliding along a vertical transform fault
D. An oceanic plate is descending beneath another plate

36 A linear volcanic island chain becomes progressively older toward the northwest, while the southeastern end is volcanically active. What does this suggest?

plate tectonics Medium
A. The plate is moving northwest over a hotspot
B. The hotspot is moving northwest faster than the plate
C. The plate is moving southeast toward a trench
D. The islands formed simultaneously along a transform fault

37 GPS stations on opposite sides of a fault move horizontally past one another, and neither side shows significant crustal creation or destruction. Which boundary is indicated?

plate tectonics Medium
A. A convergent plate boundary
B. A continental collision zone
C. A transform plate boundary
D. A divergent plate boundary

38 Why is oceanic lithosphere generally subducted beneath continental lithosphere at an ocean-continent convergent boundary?

plate tectonics Medium
A. Oceanic lithosphere is thicker than continental lithosphere
B. Continental lithosphere moves faster than oceanic lithosphere
C. Oceanic lithosphere is denser than continental lithosphere
D. Continental lithosphere contains more mantle material

39 Which tectonic development is most likely when two buoyant continental plates converge after an intervening ocean closes?

plate tectonics Medium
A. Rapid seafloor spreading and formation of an ocean ridge
B. Lateral sliding and formation of a transform valley
C. Crustal thickening and formation of a high mountain belt
D. Deep-ocean trench formation without major crustal uplift

40 Symmetrical bands of normal and reversed magnetic polarity occur on both sides of a mid-ocean ridge. What combination of processes produced this pattern?

plate tectonics Medium
A. Continental collision and repeated folding of ocean sediments
B. Seafloor spreading and periodic reversals of Earth's magnetic field
C. Transform motion and periodic shifts of the geographic poles
D. Subduction and periodic changes in ocean-water temperature

41 A crustal column is in Airy isostatic equilibrium. Relative to normal crust, a mountain range has an additional topographic elevation of . If crustal density is and mantle density is , what root thickness is required, neglecting the density of air?

isostasy Hard
A.
B.
C.
D.

42 Under Pratt isostasy, two columns have equal compensation-depth pressure. Column A consists of crust with density and surface elevation ; Column B has density . If mantle density is , what is the elevation of Column B?

isostasy Hard
A.
B.
C.
D.

43 A formerly glaciated region is rebounding, while its foreland is subsiding. Which observation most strongly indicates that the response is still approaching, rather than maintaining, isostatic equilibrium?

isostasy Hard
A. Raised shorelines become progressively younger inland
B. Present uplift exceeds the long-term erosion rate
C. Gravity anomalies remain exactly zero everywhere
D. Uplift rates decrease outward from the ice center

44 A region experiences rapid erosion that removes of rock with density . Assuming local Airy compensation and mantle density , what is the approximate surface uplift after complete flexural adjustment?

isostasy Hard
A.
B.
C.
D.

45 A broad mountain belt has little Bouguer gravity anomaly despite its high elevation. Which interpretation is most consistent with Airy isostasy?

isostasy Hard
A. The mountains are entirely uncompensated topography
B. The mountains are supported mainly by dense mantle
C. The mountains formed only through horizontal shearing
D. The mountains possess thick, relatively low-density roots

46 A crustal block is initially in local isostatic equilibrium. Sediment of density accumulates at the surface, and the block subsides without flexural rigidity. Which result is expected after equilibrium is restored?

isostasy Hard
A. Subsidence exceeds the sediment thickness
B. Subsidence equals the sediment thickness
C. Subsidence occurs only after tectonic shortening
D. Subsidence is less than the sediment thickness

47 Which combination would provide the strongest pre-plate-tectonic evidence for continental drift?

continental drift Hard
A. Cross-continental fossils, structures, and paleoclimates
B. Matching coastlines and similar modern climates
C. Symmetric seafloor anomalies and transform offsets
D. Deep trenches and active volcanic island arcs

48 Glossopteris occurs in Permian rocks of South America, Africa, India, Australia, and Antarctica. Why is this distribution more informative than a simple fit of continental shorelines?

continental drift Hard
A. It indicates the continents once shared connected terrestrial environments
B. It proves all continents had identical present-day climates
C. It demonstrates that oceanic crust is older than continental crust
D. It directly measures the speed of continental motion

49 A paleomagnetic study finds that two continents preserve remanence directions implying different apparent polar-wander paths for the same time interval. What is the most defensible interpretation?

continental drift Hard
A. The rocks must all have formed at divergent boundaries
B. Only one continent experienced magnetic reversal
C. The geomagnetic field moved independently over each continent
D. The continents changed relative positions through time

50 Why did the original continental-drift hypothesis fail to gain immediate acceptance despite strong paleontological evidence?

continental drift Hard
A. It assumed oceanic crust was composed of granite
B. It required continents to remain permanently stationary
C. It contradicted the existence of continental fossils
D. It lacked a physically credible driving mechanism

51 Permian glacial deposits occur across parts of Gondwana, yet their striation directions differ between present-day continents. Which reconstruction best resolves this pattern?

continental drift Hard
A. The deposits formed from separate equatorial ice caps
B. The striations were produced entirely by marine currents
C. The continents remained fixed while glaciers reversed flow
D. The continents joined near a common southern polar region

52 A continental reconstruction matches fossil belts but produces severe inconsistencies in paleomagnetic latitudes. Which conclusion is most appropriate?

continental drift Hard
A. The fossil data must automatically be discarded
B. The reconstruction needs testing against rock-age and remanence reliability
C. Paleomagnetism cannot constrain continental positions
D. The continents must have moved only vertically

53 A mid-ocean ridge exhibits symmetrical magnetic stripes, but the youngest crust is offset across a fracture zone. Which interpretation is correct?

plate tectonics Hard
A. Only the ridge-axis portions between offsets are active transforms
B. The ridge segments spread at different rates but have identical ages
C. The magnetic symmetry results from alternating mantle convection cells
D. The fracture zone is an active transform fault along its entire length

54 At a subduction zone, the Wadati–Benioff zone dips beneath a continent, and volcanic centers lie inland from the trench. Which process best explains the volcanic belt?

plate tectonics Hard
A. Flux melting of the mantle wedge above the slab
B. Direct eruption of unmelted oceanic lithosphere
C. Frictional melting throughout the entire crust
D. Decompression melting of the descending slab

55 A hotspot track bends sharply, while ages increase away from the active volcano. Which inference is most justified?

plate tectonics Hard
A. The volcanic chain formed entirely at a convergent boundary
B. The ridge axis instantly reversed its spreading direction
C. The hotspot necessarily migrated at the same rate
D. The plate changed motion direction or speed

56 GPS measurements show two plates moving apart, but no oceanic crust is forming between them. Which setting could explain this observation?

plate tectonics Hard
A. A locked transform boundary
B. A mature mid-ocean ridge
C. A stable intraplate craton
D. A continental rift in its early stage

57 A mountain belt contains thickened continental crust, widespread thrust faults, and little volcanic-arc activity. Which tectonic setting is most likely?

plate tectonics Hard
A. Ocean–ocean subduction
B. Continent–continent collision
C. Mid-ocean-ridge spreading
D. Intraplate hotspot volcanism

58 A trench has a negative free-air gravity anomaly, while the adjacent volcanic arc has a positive anomaly. What does this pattern most directly indicate?

plate tectonics Hard
A. A deep mass deficit at the trench and excess beneath the arc
B. A purely erosional origin for the trench and volcanic arc
C. No relationship between gravity and lithospheric structure
D. Uniformly thick continental crust beneath both features

59 A subducting oceanic plate becomes older and colder before entering a trench. Which change is most likely?

plate tectonics Hard
A. Greater slab density and stronger negative buoyancy
B. Reduced lithospheric thickness and increased buoyancy
C. Higher ridge elevation and faster crust production
D. Lower slab density and weaker sinking forces

60 Which observation would most clearly distinguish a transform plate boundary from a strike-slip fault within a plate?

plate tectonics Hard
A. The fault produces shallow earthquakes
B. The fault offsets a linear geomorphic feature
C. The fault accommodates relative motion between separate plates
D. The fault has predominantly horizontal displacement
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