Island Builders & Hotspots
This process adds new land to certain ocean islands as molten rock reaches the surface.
Answer: What is volcanic activity?
This property of magma determines how easily it flows.
What is viscosity?
This layer is the densest part of Earth.
What is the inner core?
These waves travel fastest and can move through solids, liquids, and gases.
What are P-waves?
This type of boundary forms new oceanic crust.
What is a divergent boundary?
This explains why islands farther from a hotspot tend to be older.
What is plate movement over a stationary hotspot?
Runny, low‑viscosity lava behaves most like this everyday liquid.
What is water?
Scientists study the speed of earthquake waves to infer this about Earth’s interior.
What is the composition and state of each layer?
These waves cannot travel through liquids.
What are S-waves?
This type of crust sinks when it meets continental crust because it is denser.
What is oceanic crust?
Name the major force to cause older volcanic islands to shrink over time.
Erosion
Thick, sticky magma traps gases, leading to this type of eruption.
What is an explosive eruption?
This slow-moving process in the mantle drives plate motion.
What are convection currents?
A sudden release of energy in Earth’s crust produces these waves.
What are seismic waves?
This type of boundary produces major earthquakes but little to no volcanism.
What is a transform boundary?
This type of volcano forms when runny lava spreads out in wide layers over long periods.
What is a shield volcano?
This force causes magma to rise through the crust.
What is buoyancy due to lower density?
These two sources provide most of Earth’s internal heat.
What are radioactive decay and leftover heat from formation?
A sudden drop in S-wave velocity at a certain depth indicates this type of layer.
What is a liquid layer?
This feature forms when two continental plates collide.
What are large mountain ranges?
This rock type, rich in iron and magnesium, explains why many hotspot‑formed islands have dark-colored rocks.
What is basalt?
This combination of magma characteristics creates the most dangerous volcanic hazards.
What are high viscosity and high gas content?
This rigid layer includes both the crust and the uppermost mantle.
What is the lithosphere?
The absence of S-waves on the opposite side of Earth from an earthquake helped scientists discover this.
What is the liquid outer core?
Only boundaries involving this type of crust recycle material back into the mantle.
What is oceanic crust?