Prelim 1

Question 1

When were most of the world’s natural lakes formed?

Answer 1

from 6000-15,000 years ago

Question 2

Kettle or Pothole lakes

Answer 2

Retreating glaciers leave glacial till covering large blocks of ice. Ice melts –> Lake forms. Small

Question 3

Ice-Scour Lakes

Answer 3

bedrock fractured, flat topography, often shallow, typically low nutrient

Question 4

Terminal Moraines

Answer 4

Sediments from retreating glaciers dam valleys and prevent outflow, narrow lakes, can be deep

Question 5

Cirque Lakes

Answer 5

formed at upper end of glacier by freeze-thaw cycles. Typically small, round, and often >50 m deep

Question 6

Glacial Activity Lakes

Answer 6

Kettle/pothole, ice-scour, terminal morraine, Cirque Lakes

Question 7

Graben Lakes

Answer 7

2 faults –> land drops between them, forming a lake

Question 8

Tilted Fault Block

Answer 8

One plate moves downwards relative to other, resulting in a fault or rift, Steep side and Shallow Side

Question 9

Oxbow Lake

Answer 9

River cuts a channel through bend –> erosion deposits

Question 10

Floodplain Lakes

Answer 10

Formed through erosion and/or deposition of sediments adjacent to river

Question 11

Caldera Lake

Answer 11

After eruption, lava cool and plugs and water fills

Question 12

Maar Lake

Answer 12

Volcanic explosion where magma is ejected and heats up ground water, forming steam that blasts a hole in the earth that fills with water

Question 13

What temperature is water most dense

Answer 13

3.98 Degrees Celcius

Question 14

As salinity increases density…

Answer 14

Increases

Question 15

As temperature increases density…

Answer 15

decreases

Question 16

Light Attenuation

Answer 16

The disappearance of light energy in the water column due to absorption and scattering

Question 17

Epilimnion

Answer 17

Well mixed surface waters, warm. Primary production is greater than respiration

Question 18

Metalimnion

Answer 18

Region of thermal transition; steep gradient change (usually&raquo_space;>1 degree Celsius per meter)

Question 19

Thermocline

Answer 19

Plane of steepest decline in temperature over 1 m interval

Question 20

Dimictic Mixing

Answer 20

mix twice per year

Question 21

Amictic Mixing

Answer 21

permanently ice covered, some mixing may occur under ice

Question 22

Monomictic mixing

Answer 22

mix once a year

Question 23

Oligomictic

Answer 23

stratified for much of the year, rare + irregular circulation events, no ice

Question 24

Laminar Flow

Answer 24

parcels of water move smoothly along in the same direction

Question 25

Turbulent flow

Answer 25

• while bulk flow may be unidirectional, individual particles move irregularly, more chaotic
• Causes similar mixing of heat and particles
• Responsible for mixing heat, gases, nutrients, particles

Question 26

Reynolds Number

Answer 26

Ratio of inertial forces (laminar to shear stress from turbulence
Used to predict laminar vs turbulent flow
r<500= flow is laminar
R>2000 flow is turbulent

Question 27

Meromictic Mixing

Answer 27

Chemical Stratification –> lake never mixes