Weathering and Erosion

Question 1

When and where did the Cherry Hills landslide event happened?

Answer 1

August 1-3, 1999 (Cherry Hills Subdivision, Antipolo, Rizal).

Question 2

In continuation of the previous question, the complex slide started out as a ______ and developed into a _____ near the base.

Answer 2

Slump – Debris Flow

Question 3

The steepest angle (typically less than 35 degrees) at which a sloping surface of unconsolidated sediments is stable.

Answer 3

Angle of Repose

Question 4

Provide the formula for plasticity index.

Answer 4

LIQUID LIMIT - PLASTIC LIMIT

Question 5

High Plasticity Index indicates that ________.

Answer 5

Soil can hold large amount of water.

Question 6

When did the landslide in Masara, Maco, Davao de Oro happened?

Answer 6

February 6, 2024

Question 7

What type of landform is the Marikina Valley in the Philippines?

Answer 7

Graben

Question 8

Refers to the liquid limit and plastic limit of soil.

Answer 8

Attenberg Limit

Question 9

It is the process involving varying weathering rates that influence the morphology of resulting hillslopes.

Answer 9

Differential Weathering

Question 10

The average density of Earth.

Answer 10

7 kg/cu.m

Question 11

If alluvium is for streams, _____ is for hillslopes.

Answer 11

Colluvium

Question 12

When did the Guinsaugon landslide happened and what type of mass wasting occurence happened in the area?

Answer 12

February 17, 2006 – Complex Slide (rockslide - debris avalanche)

Question 13

Define Cuesta.

Answer 13

Formed by eroding the upper edge of a gentle slope that is composed of alternating layers of hard and soft rocks.

Question 14

Mass Movements can be classified according to:

Answer 14

1. Type of movement: flow, slide, slump, etc. 2. Type of material involved: rock, debris, earth, and mud 3. Relative proportions of material and water 4. Velocity of movement: slow<>rapid 5. Thickness: shallow or deep seated 6. Type of triggering factor: rain-induced, earthquake-induced

Question 15

Define Toppling/Topple.

Answer 15

Toppling constitutes a failure in the support conditions of bedrock. A topple is a forward rotation out of the slope of a mass of soil or rock about a point below the center of gravity of the displaced mass. The process is, identically to fall, associated with very steep slopes. Topples may lead to the sliding of the displaced mass, but toppling is mostly occurring in combination with fall.

Question 16

What do you mean by denudation?

Answer 16

It is a collective term referring to the conjoint action of the physical disintegration and chemical breakdown of rocks and subsequent transportation of these rocks.

Question 17

Enumerate and define the two types of slides.

Answer 17

1. Rotational slides, which have a more or less circular failure surface. Rotational slides show in general a steep, almost vertical headscarp (crown), with the slided mass in front of it. 2. Translational slides where the sliding mass moves along a pre-existing failure plane (e.g. bedding, schistosity, joint, discontinuity between slope debris and the underlying rock).

Question 18

What is bathymetry?

Answer 18

Bathymetry is the study of the “beds” or “floors” of water bodies, including the ocean, rivers, streams, and lakes.

Question 19

Define a main scarp.

Answer 19

A steep surface on the undisturbed ground at the upper edge of the landslide, caused by movement of the displaced material away from the undisturbed ground. It is the visible part of the surface of rupture.

Question 20

Enumerate the slope classification

Answer 20

0-3 : Level to Nearly Level, 3-8 : Gently Sloping to Undulating, 8-18 : Undulating to Rolling, 18-30 : Rolling to Moderately Steep, 30-50 : Steep, >50 : Very Steep

Question 21

What is the difference between uvala and polje?

Answer 21

Uvala - A large elongate sinkhole resulting from enlargement and coalescence of a linear group of small sinkholes. Poljes - are broad, flat alluvial floor fromed from coalescence of uvalas.

Question 22

What do you mean by the surface of rupture on a landslide?

Answer 22

The surface that forms (or has formed) the lower boundary of the displaced material below the original ground surface.

Question 23

Define exfoliation.

Answer 23

Process in which layers of rock gradually break off as pressure is released from the rock.

Question 24

Factors that affect rate of chemical weathering.

Answer 24

surface area of rock exposed, rock composition, and climate

Question 25

Define moraine.

Answer 25

A deposit of sediment left behind a retreating glacier.

Question 26

Define loess.

Answer 26

deposits of wind-blown sediment

Question 27

What is a landslide flank?

Answer 27

The undisplaced material adjacent to the sides of the rupture surface. Compass directions are preferable in describing the flanks but if left and right are used, they refer to the flanks as viewed from the crown.

Question 28

What is a kettle lake?

Answer 28

bowl-shaped depression that was formed by a block of ice from a glacier and then filled with water

Question 29

How does MGB conduct geohazard mapping?

Answer 29

Interpretation and analysis of Remote Sensing Data (aerial photographs & satellite images) and other thematic maps such as geologic map, drainage map, slope map, vegetation map

Question 30

Explain how the rate of glacial erosion is controlled by four factors.

Answer 30

(1) speed of glacier movement; (2) ice thickness; (3) shape, abundance, and hardness of the rock fragments in the ice at the base of the glacier; and (4) erodibility of the surface beneath the glacier. These factors can all vary from place to place and from one time to another, with resulting variation in the degree of landscape modification.

Question 31

Narrate how the process of plucking erodes a glacier?

Answer 31

As a glacier flows over a fractured bedrock surface, it loosens and lifts blocks of rock and incorporates them into the ice. This process, known as plucking, occurs when meltwater penetrates the cracks and joints of bedrock beneath a glacier and freezes. Because water expands when it freezes, it exerts tremendous leverage that pries the rock loose. In this manner, sediment of all sizes becomes part of the glacier’s load.

Question 32

How does abrasion in glaciers occur?

Answer 32

Abrasion is the second major erosional process in glaciers after plucking. As the ice and its load of rock fragments slide over bedrock, they function like sandpaper, smoothing and polishing the surface below. The pulverized rock produced by the glacial “grist mill” is appropriately called rock flour. So much rock flour may be produced that meltwater streams flowing out of a glacier often have the cloudy appearance of skim milk and offer visible evidence of the grinding power of ice. Lakes fed by such streams frequently have a distinctive turquoise color.

Question 33

The erosional effects of valley glaciers and ice sheets are quite different. Why?

Answer 33

A visitor to a glaciated mountain region is likely to see sharp and angular topography. This is because alpine glaciers tend to accentuate the irregularities of the mountain landscape by creating steeper canyon walls and making bold peaks even more jagged. By contrast, continental ice sheets generally override the terrain and hence subdue rather than accentuate the irregularities they encounter. Although the erosional potential of ice sheets is enormous, landforms carved by these huge ice masses usually do not inspire the same awe as do the erosional features created by valley glaciers.

Question 34

How does glacial striations provide clues to the direction of ice flow?

Answer 34

The moving ice leaves the rock grains aligned with the direction of movement, so when the striation feels smooth, your finger is moving in the direction of ice flow and when it feels rough, you are moving against the ice flow.

Question 35

Explain how Cirque forms on a glacier environment.

Answer 35

The cirque is the focal point of the glacier’s growth because it is the area of snow accumulation and ice formation. Cirques begin as irregularities in the mountainside that are subsequently enlarged by frost wedging and plucking along the sides and bottom of the glacier. The glacier in turn acts as a conveyor belt that carries away the debris. After the glacier has melted away, the cirque basin is sometimes occupied by a small lake called a tarn.

Question 36

Explain the process of how sinuous, knife-edged ridges called arêtes and sharp, pyramid-like peaks termed horns are formed.

Answer 36

Both features can originate from the same basic process: the enlargement of cirques produced by plucking and frost action. Several cirques around a single high mountain create the spires of rock called horns. As the cirques enlarge and converge, an isolated horn is produced. Arêtes can form in a similar manner except that the cirques are not clustered around a point but rather exist on opposite sides of a divide. As the cirques grow, the divide separating them is reduced to a very narrow, knifelike partition. An arête can also be created when glaciers that flow in parallel valleys narrow the intervening ridge as they scour and widen their valley

Question 37

How are roche moutonnée formed?

Answer 37

They are formed when glacial abrasion smooths the gentle slope facing the oncoming ice and plucking steepens the opposite side as the ice rides over the knob.

Question 38

How are Froids formed?

Answer 38

Fiords are deep, often spectacular steep-sided inlets of the sea that are present at high latitudes where mountains are adjacent to the ocean They are drowned glacial troughs that became submerged as the ice left the valleys and sea level rose following the Ice Age. The depths of fiords may exceed 1000 meters (3300 feet).

Question 39

Why doesn't sea level work as a base level for glaciers?

Answer 39

Unlike the situation governing the downward erosional work of rivers, sea level does not act as base level for glaciers. As a consequence, glaciers are capable of eroding their beds far below the surface of the sea. For example, a 300-meter- (1000-foot-) thick glacier can carve its valley floor more than 250 meters (820 feet) below sea level before downward erosion ceases and the ice begins to float.

Question 40

How do glaciers acquire their load of sediment?

Answer 40

Glaciers acquire their load of sediment due to the movement of the ice, which scours the bedrock and accumulates sediment. Glaciers are very large and very heavy, so they exert a lot of pressure. As they flow, this pressure pulls boulders out of the ground and grinds them underneath the glaciers.