stress and strain

Question 1

stress

Answer 1

the force applied to rocks

Question 2

strain

Answer 2

a change in the shape or volume of a body as a result of applied stress

Question 3

competent

Answer 3

rocks are strong and brittle and tend to join and fault

Question 4

incompetent

Answer 4

rocks are weak and plastic and tend to fold and develop cleavage

Question 5

tension

Answer 5

the force trying to pull rocks apart, the Earth’s crust will be lengthened

Question 6

compression

Answer 6

the force trying to push rocks together, the earth’s crust will be shortened

Question 7

shear

Answer 7

forces are those which act along a plane in the rock and promote sliding along that plane

Question 8

joint

Answer 8

a fracture in competent rocks along which no observable movement has occurred

Question 9

name 2 competent rocks

Answer 9

sandstone

limestone

Question 10

name 2 incompetent rocks

Answer 10

clay

shale

Question 11

how do joints form?

Answer 11

they’re produced by tensional forces. these forces may result due to folding, cooling or unloading of rocks.

Question 12

what type of rock do joint form in?

Answer 12

competent

Question 13

how are joint in sedimentary rocks usually found?

Answer 13

perpendicular to beds

Question 14

how are tectonic joints produced?

Answer 14

The tension created in rocks when they are folded by earth movement. The rocks fracture because the outer surface of the bed is stretched more than the inner surface.

Question 15

what are the 2 types of tectonic joints?

Answer 15

tension joints- parallel to the axial plane trace

cross joints- at an angle to the axial plane trace of the fold

Question 16

how do cooling joints forms?

Answer 16

they’re caused by tensional forces set up in igneous rocks as it cools steadily and contracts, forming polygonal columnar jointing perpendicular to the cooling surface.

Question 17

how do unloading joints form?

Answer 17

Form in igneous rocks which cooled deep below surface where pressure is high. Mass of overlying rocks compressed the rock. Rock is exposed at surface (uplift and erosion), lack of load pressure allows them to expand. Joints form roughly parallel to earths surface