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Chapter 8: Problem 27

Explain the criteria you would apply to images (assume adequate resolution) in order to distinguish between a crater formed by an impact and one formed by a volcanic eruption.

Short Answer

Expert verified
Examine shape, ejecta patterns, presence of lava, crater wall structure, and surrounding geological features.

Step by step solution

01

Determine Shape and Structure

Examine the overall shape of the crater. Impact craters are usually circular with a raised rim and a central peak caused by the rebound of the ground. Volcanic craters may have an irregular shape and lack a central peak.
02

Check for Ejecta Patterns

Look for patterns of ejecta around the crater. Impact craters often have well-defined ejecta blankets surrounding them. These blankets are made from materials that were excavated and thrown out during impact. Volcanic craters typically have pyroclastic flows and lava deposits rather than ejecta blankets.
03

Identify the Presence of Lava

Observe if there are signs of lava flows inside or around the crater. Lava is an indication of volcanic activity. Impact craters will not have these lava formations within or near the crater.
04

Analyze the Crater Walls

Study the walls of the crater. Impact craters usually have steep walls with terracing due to the collapse of the crater's sides. Volcanic crater walls are generally less steep and exhibit signs of layering from successive lava flows.
05

Consider the Surrounding Geological Features

Examine the area surrounding the crater for related geological features. Volcanic craters are often found in regions with other volcanic formations such as volcanic cones or calderas. Impact craters may be isolated and show shock metamorphism in surrounding rocks.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

impact craters
Impact craters are formed when a meteoroid, asteroid, or comet strikes a planet or moon at high velocity. These craters are usually circular due to the explosive nature of the impact. The force of the impact compresses the ground, creating a raised rim and sometimes a central peak. This central peak is a result of the ground rebounding after the impact.
**Characteristics of Impact Craters**:
  • Circular Shape: Generally very circular with a raised rim.
  • Ejecta Patterns: Surrounding the crater, you'll find ejecta blankets made of material excavated during the impact.
  • Steep Walls: The walls are often steep and exhibit terracing due to the collapse of the crater walls.
  • Central Peak: Some larger impact craters display a central peak caused by ground rebound.
  • Shock Metamorphism: Rocks around the crater show signs of high-pressure deformation.
These distinguishing features help in identifying impact craters when examining images. By looking at the shape, walls, and surrounding ejecta, one can conclude the crater's origins.
volcanic craters
Volcanic craters are formed by volcanic activity, usually at the summit of a volcano. Unlike impact craters, they are less circular and may have an irregular shape. These craters form when the top of a volcano collapses into an empty magma chamber below.
**Characteristics of Volcanic Craters**:
  • Irregular Shape: The shape can vary and is not as uniformly circular as impact craters.
  • Lava Deposits: You'll often find lava flows inside or around the crater.
  • Less Steep Walls: The walls are generally less steep and show layering due to successive lava flows.
  • Pyroclastic Flows: Instead of an ejecta blanket, volcanic craters feature pyroclastic deposits.
  • Geological Context: These craters are usually located in volcanic regions with other related formations.
Recognizing volcanic craters involves examining their shape, wall structure, and the presence of lava flows. The geological context plays a crucial role as these craters are often part of larger volcanic systems.
ejecta patterns
Ejecta patterns are crucial in distinguishing between impact and volcanic craters. Ejecta refers to the material thrown out of a crater during its formation.
**Impact Craters:**
  • Ejecta Blankets: Look for well-defined layers of debris spreading out from the crater. This material is excavated and flung outward during the impact.
  • Radial Patterns: The distribution often follows radial patterns as material is ejected in all directions.

**Volcanic Craters:**
  • Pyroclastic Flows: Instead of ejecta blankets, volcanic craters feature flows of ash, rock fragments, and volcanic glass.
  • Less Uniform Distribution: The material is spread differently, not in uniform radial patterns.
By observing the surrounding area for these patterns, one can infer the type of crater. Impact craters show distinct, uniform ejecta patterns, whereas volcanic craters exhibit more varied deposits.
lava flows
Lava flows are essential indicators of volcanic activity and play a significant role in identifying volcanic craters. Lava is molten rock that erupts from a volcano and solidifies upon cooling.
**Location and Formation:**
Lava flows are typically found within or around volcanic craters. They form as lava pours out during an eruption and spreads across the landscape.
**Characteristics of Lava Flows:**
  • Texture and Composition: Lava solidifies to form rugged or smooth surfaces, depending on its viscosity and the speed of flow.
  • Layering: Successive lava flows can create layered structures, particularly within the walls of volcanic craters.
Lava flows are not found in impact craters, making their presence a definitive indicator of volcanic origins. Observing these formations helps in accurately identifying volcanic craters.
crater walls
The structure and composition of crater walls provide significant clues about the crater's formation. By carefully analyzing the walls, one can distinguish between impact and volcanic craters.
**Impact Craters:**
  • Steep Walls: The walls are often very steep and may show terracing from the collapse of the crater's sides.
  • Central Uplift: Larger impact craters can have a central peak caused by the rebound of the ground.

**Volcanic Craters:**
  • Layered Walls: Volcanic craters have walls that show clear layering from successive lava flows.
  • Less Steep Walls: Generally, these walls are less steep compared to impact craters.
Analyzing the crater walls helps in determining the crater's origin. The difference in wall structure and composition is a key factor in this identification process.

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Most popular questions from this chapter

Suppose you find a piece of ancient pottery and find that the glaze contains radium, a radioactive element that decays to radon and has a half-life of 1,620 years. There could not have been any radon in the glaze when the pottery was being fired, but now it contains three atoms of radon for each atom of radium. How old is the pottery?

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