Holes and Highways: The Porosity Permeability Quiz

If a rock is not a solid block but is made of grains or contains cracks, then empty spaces exist between those solids. If we calculate the ratio of those empty spaces to the total volume of the rock, then we have determined the rock's porosity.

If a material has many pores, it has high porosity, but if those pores are not connected, the water cannot travel. If the pores are interconnected so that water can flow from one to another, then the material has permeability.

If a rock has many tiny holes, then it has high porosity. If those holes are isolated and not connected to each other (like in pumice or bubble wrap), then water cannot flow through it. If water cannot flow, then the permeability is low despite the high porosity.

If permeability depends on the size of the pathways between particles, then larger particles create larger pathways. If gravel consists of large pieces with large gaps between them, then water flows through it much faster than through the tiny, tight spaces in clay or solid rock.

If a sediment is poorly sorted, then smaller grains fill the gaps between the larger grains. If those gaps are filled with smaller solids, then there is less empty space (porosity) remaining. Therefore, well-sorted sediment with consistent gaps remains more porous.

If a geological unit has high enough porosity to store water and high enough permeability to allow that water to be pumped out, then it serves as a functional water source. In earth science, such a productive water-bearing layer is defined as an aquifer.

If clay is made of extremely small, flat particles, then the pores between them are microscopic. If the pores are microscopic, then the surface tension and electrical attraction between water and clay keep the water trapped. If the water is trapped and cannot flow, the permeability is low.

If water moves through pores, then the size of the "tunnel" affects the friction the water encounters. If the pores become smaller, then the friction increases and the flow path becomes more restricted. If the flow is restricted, then the permeability is lower.

If sediment is buried under more layers, then the weight of the overlying material increases. If the weight increases, then the grains are squeezed closer together and the air/water is pushed out. If the grains are squeezed together, then the total volume of open space (porosity) is reduced.

If a layer of material has very low permeability (like thick clay or solid rock), then it acts as a barrier to water movement. If it significantly slows down or prevents the passage of water into an aquifer, then it is classified as an aquitard.

If porosity is the percentage of pore space in a total volume, then the formula is (porevolume/totalvolume)×100. If we plug in the numbers (10025​)×100, then the resulting percentage is 25%.

If an aquitard must stop water flow, then it needs the lowest permeability possible. If compacted clay has the smallest, most disconnected pores of the choices provided, then it will hinder water flow the most effectively.

If a well is drilled, it needs to be refilled by the surrounding groundwater as water is pumped out. If the rock has high permeability, then water can flow quickly into the well pipe. If the permeability is too low, the well will run dry almost immediately because water cannot move through the rock to refill it.

If water needs to travel from point A to point B through a rock, then it must have a continuous path of openings. If the pores are "interconnected," then such a path exists. If such a path exists, then the rock is permeable; otherwise, the water remains trapped in individual bubbles.

If we want to model the rate of groundwater flow based on permeability and pressure, then we use a specific mathematical relationship. If this relationship was discovered by Henry Darcy in 1856, then it is known as Darcy's Law.

If particles are the same shape (spheres) and are sorted perfectly, then the ratio of empty space to solid stays the same regardless of the size of the spheres. If the geometry remains constant, then the percentage of "hole" space remains roughly equal (usually around 35-45%).

If basalt has gas bubbles (vesicles), then it has high porosity. However, if those bubbles formed as the lava cooled and did not pop or connect, then they are "closed-cell" spaces. If the spaces are closed, then water cannot flow between them, meaning the permeability is low.

If a solid rock is broken or cracked (fractured), then new, wide pathways are created for water to travel. If these paths are much wider and more connected than the original pores, then the ability of water to flow (permeability) increases significantly.

If water infiltrates the ground, it eventually reaches a depth where gravity has pulled enough water to fill every available gap. If no air is left in the pores and only water remains, then the material has reached its limit and is called the saturated zone.

If grain shape and size determine the size of the gaps, then they influence flow. If pore connectivity determines the path of the water, then it also influences flow. If color and the Sun do not affect the physical path through the rock, then only A, B, and D are correct.