SCIENCE · INVESTIGATE AND EXPLAIN

Distinguish weathering from movement

Compare fictional fragmentation, alteration, transport and ambiguous-color evidence.

Learning outcome: Justify a process interpretation from supplied observations rather than appearance alone.

Starting recap

Physical weathering fragments material; chemical weathering changes minerals; transport moves material.

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Try

Feldspar alteration with clay and dissolved products supplies different evidence from fragments alone.

Open the experiment

Predict

Does a brown appearance uniquely identify chemical alteration?

Your prediction and reason

Experiment

Sort the four fictional cards into observations and interpretations; retain alternatives for the brown surface and propose a discriminator.

Compare storm timing and initial water storage

Original sealed-store experiment · separate weathering evidence practice · Original synthetic plot with 40 mm storage capacity and maximum entry 15 mm/hour. Rain is piecewise constant by hour. Infiltration is limited by rain supply, entry limit and remaining storage; unentered rain leaves immediately as runoff. No drainage, evapotranspiration, surface ponding, routing or empirical soil forecast. Entry stops at a full store only because this store has no drainage; real saturated soil can transmit water. Exact rate segments split at filling time; stored water is not runoff.

Initial water in teaching store: 0 mm Six-hour rain profile: Uniform: 60 mm over six hours

Reset keeps your prediction, captures and practice history.

Weathering changes material; erosion moves it

Original fictional observation cards. The rain controls do not change these cards or simulate weathering. Before revealing an interpretation, identify whether the evidence supports physical fragmentation, chemical alteration, transport, or an unresolved mechanism. Real exposures may show several processes together.

Supplied qualitative evidence, not measurements from a field site
Case	Evidence to explain	Prediction task
A: broken sample	A rock breaks along cracks into smaller pieces. Mineral tests before and after show the same mineral constituents.	What changed, and what was conserved?
B: altered minerals	Mineral tests show loss of some original feldspar and formation of clay minerals; dissolved constituents occur in water leaving the sample.	Does fragmentation alone explain all observations?
C: relocated grains	Marked grains leave one patch during flowing water and accumulate downstream; their tested mineral constituents remain unchanged.	Separate removal, transport and deposition.
D: a brown surface	A photograph shows a brown coating. No mineral or chemical analysis is supplied.	What additional evidence distinguishes oxidation, staining or another coating?

Compare the weathering interpretations

A supports mechanical fragmentation; the stated evidence does not establish chemical alteration. B supports chemical weathering, including mineral transformation and dissolved export; real reactions require appropriate conditions and cannot be identified from color alone. C supplies erosion, transport and deposition evidence, not proof of new chemical weathering. D remains ambiguous: obtain compositional evidence and compare coated material with the underlying rock.

Water entering cracks, crystal growth and roots can contribute to physical breakdown under suitable conditions. Chemical weathering includes dissolution and reactions involving water, oxygen or acids. These processes can interact: new cracks expose surfaces, while alteration can weaken rock. A crack or weather event by itself does not establish an exact weathering rate.

Fragmentation exposes more surface

Original geometry: begin with a cube 2 cm on each edge. Cut every edge into equal divisions and separate all pieces so every face is accessible. Predict the total exposed area before opening the table. Cutting changes shape and exposure; it does not itself change mineral identity or create material.

Reveal area and volume calculations

All faces exposed; no material lost and no chemical reaction modeled
Divisions per original edge n	Pieces n³	Piece edge cm	Total volume cm³	Total area cm²
1	1	2	8	24
2	8	1	8	48
4	64	0.5	8	96

Each of n³ pieces has edge 2/n cm and six faces. Total area = n³ × 6 × (2/n)² = 24n cm². Total volume = n³ × (2/n)³ = 8 cm³. The area grows in proportion to n, while volume stays fixed. More available surface can change reaction opportunities, but temperature, composition, water supply, chemistry and accessible contact also matter. Twice the area does not guarantee twice the observed weathering rate.

Transfer: use a 3 cm starting cube divided into three pieces per edge. Calculate piece count, total volume and area, then identify why tightly packed pieces might not expose every face to moving water.

Background: National Park Service weathering mechanisms and USGS explanation of clay formation and weathering. These sources explain real processes; the cards and cubes here are teaching constructions.

Original storm experiment: entry and storage are different limits

Uniform: 60 mm over six hours. The receiving store holds at most 40 mm of water equivalent and admits at most 15 mm/hour while space remains. Rain that does not enter leaves the plot immediately. This is an intentionally sealed teaching store: no drainage, evapotranspiration, surface ponding or travel time is included. Real saturated soil can transmit water; these parameters are not measured soil properties.

Conservation: initial storage + rain = final storage + runoff. For this case, 0 + 60.0 = 40.0 + 20.0 mm. Newly infiltrated water equals the storage increase only because this model has no store outflow. Initial water is not counted again as new infiltration.

Read rates and accumulated water separately

The model store first fills at hour 4.0000. A full store and an exceeded entry-rate limit are distinct reasons why rain may leave as runoff.

One-hour totals; quantities are mm of water equivalent
Hour interval	Rain	Initial store	Infiltration	Runoff	Final store
0–1	10.0	0.0	10.0	0.0	10.0
1–2	10.0	10.0	10.0	0.0	20.0
2–3	10.0	20.0	10.0	0.0	30.0
3–4	10.0	30.0	10.0	0.0	40.0
4–5	10.0	40.0	0.0	10.0	40.0
5–6	10.0	40.0	0.0	10.0	40.0

Inspect exact rate intervals and the filling event

Within-hour rate changes occur at calculated filling times
Start–end hours	Rain mm/hour	Infiltration mm/hour	Runoff mm/hour	Store start–end mm
0.0000–1.0000	10	10	0	0.00–10.00
1.0000–2.0000	10	10	0	10.00–20.00
2.0000–3.0000	10	10	0	20.00–30.00
3.0000–4.0000	10	10	0	30.00–40.00
4.0000–5.0000	10	0	10	40.00–40.00
5.0000–6.0000	10	0	10	40.00–40.00

For a one-hour bin, entry depth is the minimum of rain depth, 15 mm and remaining storage. Before filling, entry rate is the smaller of rain rate and 15 mm/hour. Time to fill is remaining storage divided by that rate. If the rate is zero, no filling time is calculated from division by zero. At filling, entry stops and the rest of the rain leaves; the plot is not drawn as though the average hourly entry occurred uniformly.

Choose a fair comparison and explain its limits

Compare uniform and concentrated storms from the same initial storage: both supply 60 mm, isolating timing in this model. Light rain supplies 20 mm and the dry case supplies zero, so those comparisons also change total input. With initial storage zero, uniform rain admits 40 mm and exports 20 mm; the concentrated storm admits 30 mm and exports 30 mm. With 20 mm initially stored, both export 40 mm, but the time patterns differ.

Real runoff depends on drainage, surface storage, soil structure, vegetation, slope and spatial connections omitted here. This plot's immediate export is not a catchment outlet hydrograph. Runoff depth alone does not determine sediment mass; that requires concentration or sediment-process evidence. Background: USGS surface runoff and USACE infiltration and runoff-volume concepts.

Rain 60.0 mm = runoff 20.0 mm + storage increase 40.0 mm.

Initial store 0 mm; final store 40.0 mm. Store first full at hour 4.000. Full means the sealed teaching store is full, not a diagnosis of real soil saturation; real saturated soil can transmit water. Synthetic bounded accounting, not a catchment forecast.

Observation to attach to a capture

Captures preserve initial water storage and the synthetic storm profile. Replay recalculates the sealed-store comparison; it does not measure real runoff, simulate weathering or establish an independent field result.

Understand

Describe a change before naming its cause

A rock has become smaller, browner or surrounded by fragments. Those observations can suggest questions, but they do not all establish the same process. Start with the four fictional evidence cards. For each, make two columns: what the card supplies and what you infer from it. These are authored teaching records, not measurements collected from an actual outcrop.

Weathering breaks material down or chemically alters it where it is. Erosion removes material, transport moves it, and deposition leaves it in a new location. Several processes can occur in one history. The National Park Service weathering explanation distinguishes physical fragmentation from changes in mineral chemistry. The distinction concerns evidence of the process, not just the appearance of its final product.

Compare fragmentation with chemical alteration

Card A supplies fragmentation. Smaller pieces form while the supplied mineral evidence does not indicate a change in their chemical composition. That supports physical weathering in this fictional case. Draw the original outline and its separated fragments. Label the break surfaces; do not add a chemical product merely because the pieces are smaller.

Card B supplies feldspar alteration associated with clay and dissolved material. Those observations support chemical weathering rather than fragmentation alone. Put the original mineral, changed solid products and dissolved material in separate boxes. Matter entering solution has not disappeared from a conservation account even if less solid material remains visible.

A chemical-weathering interpretation needs mineral or chemical evidence, not merely a claim that water was nearby. Water can also transport particles or participate in mechanical changes. Conversely, physical fragmentation can expose additional surfaces where later chemical reactions occur. The categories distinguish mechanisms without insisting that they never interact.

Water freezing in suitable cracks and roots widening openings are two possible physical mechanisms. Dissolution transfers mineral constituents into solution; oxidation involves chemical reaction with oxygen. Each requires appropriate conditions and evidence. Neither a crack nor a brown surface alone establishes which process occurred, its rate or the amount altered.

Keep transport separate

Card C supplies movement of material. That supports transport, not a complete explanation of how the particles originally formed. Sketch an arrow from the original location to the new one and write “weathering history unresolved” beside it unless the card supplies further evidence.

Connect this with the earlier sediment investigation: material crossing a gauge may have been detached earlier and stored upstream. A transport total is not automatically new chemical weathering, new physical fragmentation or gross erosion across a whole watershed. An accurate movement observation can be useful while its source history remains uncertain.

Retain an ambiguous color change

Card D supplies a brown appearance without enough supporting evidence to establish its cause. Keep more than one candidate rather than forcing a weathering label. Mineral alteration, a coating, staining or lighting could require different observations to distinguish. Color alone does not tell you which reaction occurred or how fast it proceeded.

Write a discriminating observation for D: for example, comparing mineral composition or examining whether the color belongs to a surface coating. State what finding would support your proposed explanation and what would weaken it. The browser does not perform that analysis, so record it as a next investigation rather than an obtained result.

Use geometry without inventing a reaction rate

A separate original cube example cuts a 2 cm cube into eight 1 cm cubes and separates them. Volume remains eight cubic centimeters, while total exposed surface grows from 24 to 48 square centimeters. This arithmetic shows a possible change in contact area. It neither proves chemical alteration occurred nor calculates a weathering rate.

Predict which card could involve such fragmentation and which needs composition evidence. Keep the fictional rock cards and cube geometry separate from the storm model: changing rainfall controls does not numerically weather a rock or manufacture sediment.

Transfer: repair an overconfident field note

An unfamiliar note says, “The rock is brown and smaller, so chemical weathering dissolved half its mass.” It contains no before-and-after mass, mineral analysis or dissolved-water measurements. Identify two missing links and write a bounded replacement.

Check the weathering-evidence transfer

Color and apparent size do not establish a specific chemical reaction or a quantified dissolved mass. Fragmentation, coatings and transport remain possible. A defensible note records the visible appearance and requests comparison of mineral composition, material inventory and relevant dissolved constituents before claiming a mechanism or mass loss.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Separate material change, transport and an unmeasured reaction history.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Defend a bounded geological interpretation Next: Compare exposed area after fragmentation

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