ENV 100 Chap.6 Asteroids, Glaciations, and Surface Change
Asteroids, Glaciations, and Surface Change
This chapter treats impacts and glaciations as different triggers for a common resurfacing chain: weathering, erosion, transport, deposition, compaction, cementation, and lithification. It uses deposit sorting, graded bedding, moraines, outwash, diamictites, crustal loading, rebound, and sea-level change as evidence of process.
What this chapter covers
- 01
Resurfacing process chain
- 02
Impact disturbance and traces
- 03
Clastic sedimentary rocks
- 04
Graded bedding
- 05
Ice-sheet erosion and deposition
- 06
Isostatic loading and rebound
Worked example · free
Distinguish moraine from outwash
- +1Identify poor sorting in the ridge.
- +1Link the ridge with direct ice deposition.
- +1Identify layering and sorting on the plain.
- +1Link the plain with meltwater transport.
Key terms
- Weathering
- Weathering is physical, chemical, or biological breakdown of material in place.
- Erosion
- Erosion is the removal of weathered or exposed material by a moving agent.
- Lithification
- Lithification is compaction and cementation that turn sediment into rock.
- Moraine
- A moraine is a ridge or accumulation of sediment deposited directly by glacier ice.
- Outwash
- Outwash is sediment transported and sorted by meltwater beyond an ice margin.
Asteroids, Glaciations, and Surface Change FAQ
What evidence can indicate an impact?
Crater form, shocked or melted material, unusual density contrasts, ejecta, and correlated sediment layers can converge on an impact interpretation. A single unusual layer is not sufficient by itself.
How does ice deform Earth's crust?
Growing ice loads depress the crust and mantle beneath it. When ice melts, removal of the load allows gradual rebound, changing land elevation and local relative sea level.
Where does graded bedding form?
It forms when a sediment-laden flow loses energy and grain sizes settle in a systematic sequence. The structure records changing transport conditions rather than merely a list of particle sizes.
How do weathering and erosion differ?
Weathering breaks material down in place through physical, chemical, or biological processes. Erosion removes material and begins transport by water, ice, wind, or gravity. Keeping location and movement explicit prevents the two stages from being collapsed into one vague surface process.
What makes a glacial interpretation stronger?
Combine landform position with sediment texture, sorting, internal structure, and relation to former ice or meltwater pathways. A ridge shape may suggest a moraine, but direct ice deposition is more convincing when the material and regional pattern fit the same reconstruction.
Assessment move
Organise the chapter around a resurfacing sequence: weathering breaks material down in place, erosion removes it, transport moves it, deposition stores it, and compaction plus cementation can preserve it as rock. Write each process on a separate card and arrange the cards for different agents such as ice, meltwater, gravity, wind, and impact disturbance.
This reveals where the common sequence remains useful and where a trigger changes the route. Build one event-to-deposit chain for an asteroid impact and another for glaciation. For the impact, begin with energy release and excavation, then add crater geometry, fractured or melted material, ejecta, and possible sedimentary traces.
For glaciation, begin with accumulation and ice movement, then add erosion, loading, direct deposition, meltwater sorting, and rebound after unloading. Compare moraine and outwash using agent, sorting, structure, and position rather than relying on landform shape alone. Draw a simple sedimentary log and practise reading vertical order as time at one location.
Then draw a map and practise reading horizontal distribution as space. For graded bedding, explain how changing flow energy produces a sequence instead of merely naming coarse and fine layers. Add isostatic loading and rebound to the sea-level discussion by distinguishing land movement from water-volume change. Retrieval practice should ask for evidence before labels.
Given an unsorted ridge, list at least two observations needed to support direct ice deposition. Given a circular structure, identify the shocked, melted, geophysical, or regional evidence that would strengthen an impact interpretation. Use conditional language when one trace has several possible origins.
Once a week, write a comparison paragraph with matched criteria and a final sentence describing what observation would overturn the preferred explanation. For test preparation, sketch an agent, pathway, deposit, and preserved structure in four minutes. Audit the result for agent, energy, texture, geometry, and scale.
The final check is chronological: make sure the proposed cause occurs before the deposit and that later erosion or lithification has not been mistaken for the original event.
