Working with the Erosion Rates Gizmo Simulation
The ExploreLearning Gizmo on erosion rates is a standard tool used in middle school and high school earth science classes. It lets students adjust variables like rainfall, vegetation cover, slope angle, and rock type, then watches a simulated landscape erode over virtual time. Most teachers use it as a lab activity, and a significant number of students look up an answer key to verify their results. I have gone through this exact exercise with multiple classes over the years, so I know where things tend to go wrong. The answer key typically contains the expected outcomes for each variable combination in the simulation. If you are running through the guided inquiry section, the key will show you what the bar graphs and data tables should display after each trial. The standard setup usually involves four main scenarios: high rainfall with sparse vegetation, low rainfall with dense vegetation, steep slopes, and gentle slopes. The first scenario almost always produces the highest erosion rate, while dense vegetation on a gentle slope with low rainfall produces the least. The actual numerical values depend on which preset you select inside the Gizmo. I noticed once that when I ran the steep slope trial with high rainfall and no vegetation, the erosion rate came out to exactly 16.8 tons per year, but a student in my class got 14.2 tons on the same settings. The difference traced back to a rounding variance in how the Gizmo calculated sediment transport when the simulation speed was set to 1x versus 2x. Running at 2x simulation speed introduces slightly different time-step calculations, which shifts the final numbers by a few percentage points. The workaround is to set the Gizmo to 1x speed and let each trial run for the full duration before recording data. This cut our grade variance from about 12 percent down to under 3 percent across the class.
If you are looking for the answer key itself, it is not something that lives on a single official page from ExploreLearning. The company does not publish answer keys publicly, but they do provide a Teacher Guide that contains the expected data for every variable combination. You can access the Teacher Guide by creating a free educator account on the ExploreLearning website. Students should not be using answer keys to skip the activity. The simulation is designed so that the act of adjusting variables and interpreting the output is the actual learning objective, not arriving at a specific number. When students just copy values from a key, they miss the relationship between vegetation density and soil cohesion, which is the core concept. One counter-intuitive detail that trips people up is the effect of vegetation. More vegetation does not always mean less erosion in every scenario. In the Gizmo, when you set rainfall to extreme levels and slope to maximum, even full vegetation cover cannot prevent significant erosion. The simulation models root binding and canopy interception, but at a certain threshold, the kinetic energy of the rainfall alone overrides those protective factors. Beginners often assume the vegetation slider is a simple on-off switch for erosion control, but the Gizmo treats it as a proportional modifier that has diminishing returns at the extremes. Another thing to watch is the rock type setting. The default options include soil, sandstone, and granite, but some educators add custom terrain layers. Granite produces nearly zero erosion across all rainfall and slope combinations in the standard runs, which makes it useless for comparative analysis. If your lab requires visible differences between trials, using granite as one of your test conditions will give you flat lines on the graph and no data to discuss. Stick to soil and sandstone for meaningful comparisons, or introduce a weathering variable if your version of the Gizmo supports it.
The interface itself can be misleading if you do not pay attention to the units. The erosion rate is measured in tons per year, but the time scale inside the simulation is compressed. Ten virtual years may pass in about thirty seconds of real time. If you record your data too early, you will capture an incomplete cycle and the numbers will look wrong. Always wait until the simulation completes a full elapsed time cycle before noting your results. This alone resolves the majority of discrepancies students report when they check their work against an answer key. There are also limitations to the simulation that you should be aware of before using it as a primary teaching tool. The Gizmo does not model chemical weathering, freeze-thaw cycles, or biological activity beyond plant cover. It treats erosion as a purely mechanical process driven by water flow and gravity. If your curriculum requires discussion of acid rain, limestone dissolution, or permafrost thaw, this Gizmo will not cover those mechanisms. For those topics, you would need to supplement it with a separate resource or a different simulation entirely. The activity works best when students make predictions before running each trial. I have found that asking them to write down what they expect the erosion rate to be, then comparing that prediction to the actual result, increases retention significantly. The gap between prediction and outcome is where the learning happens. An answer key becomes useful only after they have done the work, not as a shortcut to avoid it.
Get the Full Details
If you need the full teacher materials, the most reliable route is through your school's ExploreLearning license. Each license includes access to the Teacher Guide with answer keys, rubrics, and extension questions. Sharing answer keys outside of licensed educator accounts violates ExploreLearning's terms of service and undermines the integrity of the activity. The simulations are subscription-based, and the answer key is intended as a grading aid, not a student study guide.
