Sedimentary

Question 1

Why is there a difference between the minimum erosion velocity and the maximum deposition velocity of a particle

Answer 1

-greater velocity is required to overcome inertia of the grain
-once moving it has momentum so less velocity required to keep it moving
-more energy needed to pick up than deposit

Question 2

Why does the critical erosion velocity on a hjulstrom graph increases for particles smaller than 1mm

Answer 2

• higher velocity to produce the energy required to separate the clay particles
• which have flocculated
• because of a small charge
• cohesion
• stick together

Question 3

Why are grains well sorted in a fluvioglacial deposit

Answer 3

• Because stream velocity would have been fairly constant
• transporting finer material downstream

Question 4

How do we know that a sediment is fluvioglacial rather than glacial origin

Answer 4

Fluvioglacial sediments are
- rounded
- because of attrition
- sorted
- imbricated (overlap)
- indicate a unidirectional flow

Question 5

What are physical characteristics of sediment particles that could influence the pick up, transport and deposition

Answer 5

• particle size
• particle density
• particle shape

Question 6

Why are high stream velocities required to pick up particles smaller than 0.1mm

Answer 6

• smaller particles have higher cohesion
• greater charge per unit area
• water can’t get between/beneath grains
• smaller particles do not stick up so far in flow
• present a smooth surface which is more resistant

Question 7

Once very fine grained particles (clay) are picked up how are they deposited on reaching the sea

Answer 7

• low energy/stagnant water - mud flats of estuary
• flocculation of particles when they reach the sea
• sea is an ionic solution which reduces the charge in the particles which prevent particle collision
• therefore clay particles collide and fall out of suspension

Question 8

What are possible causes of a turbidity flow

Answer 8

• earthquake
• storm
• slump