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LAB 10: Arid Features, Climates & Landforms

Drylands Nearly 30% of the Earth's land surface is desert, arid land with minimal rainfall that supports only sparse vegetation and a limited population of people and animals. Deserts have been portrayed as fascinating environments of adventure and exploration from narratives such as that of Lawrence of Arabia to movies such as Star Wars. They may be hot, they may be cold. They may be regions of sand or vast areas of rocks and gravel peppered with occasional plants. But deserts are always dry (USGS). There are almost as many definitions of deserts and classification systems as there are deserts in the world. Most classifications rely on some combination of the number of days of rainfall, the total amount of annual rainfall, temperature, humidity, or other factors. In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall, arid lands have less than 250 millimeters of annual rainfall, and semiarid lands have a mean annual precipitation of between 250 and 500 millimeters. 1. What are the names and details of the three widely used classifications of deserts? Below is a diagram of the large deserts found on our planet, as well as their aridity as pictured in the legend. 2: What does this map say about the western United States? 3: What other places on earth match the same level of aridity as the western United States?

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Climagraphs A quick way to get an idea of the climate of a particular place is to look at a "climate-graph," or "climograph." A climograph is what scientists create to show a particular location's average temperature and precipitation during the year. Below is a climagraph from Death Valley, California. 4. Based on the provided precipitation values found on this climagraph, what type of ‘desert’ is Death Valley—and why?

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Köppen’s Climate Classification Vladimir Köppen was a German climatologist who came up with a simple climate classification system based on a place’s temperature and precipitation. While not perfect, it can provide a quick idea as to what weather a place experiences throughout the year. Every location in the world can be given a three letter classification based on annual weather data. Sacramento, California is a Csa climate. Bishop, California is a BWk climate. World climates are placed into one of six major classifications:

A = Tropical climates C = Mesothermal(mild mid-latitude) climates D = Microthermal(cold mid-latitude) climates E = Polar climates B = Dry climates H = Highland climates

5. Based on what you know about California geography and descriptions (and from the options above), which major climate classifications will you not see in California? Why not? As an example: Every location that falls into one of the first four climate classifications (A, C, D, and E) also has two lowercase letters following the main classification. The second letter in these climates refers to when precipitation occurs.

f = precipitation falls all year w = winter dry, summer wet s = summer dry, winter wet

The third letter tells you about the average monthly temperature extremes.

a = hot summers, warmest month above 72° F b = warmest month below 72° and four months or more above 50° c = warmest month below 72° and three months above 50° d = coldest month below -35° e = warmest month below 50°

As mentioned above, Sacramento, California is a Csa climate. The “C” means it is a Mesothermal climate. The “s” means rain falls during the winter and not the summer and the “a” means that it has hot summers. Climates that fall into the “B” classification are treated differently. A climate that falls into this category is either an arid or semiarid climate. Arid means that the annual precipitation is less than ½ of the annual evapotranspiration. These climates are given a “W” after the B. Semiarid climates have annual precipitation greater than ½ but still less than the annual evapotranspiration. They are given an “S”. The third letter for these climates refers to annual average temperatures. A lowercase “h” means the mean annual temperature is above 65° F and a lowercase “k” means the mean annual temperature is below 65° F. As mentioned above, Bishop, California is a BWk climate, meaning it is an arid desert with cold winters.

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Applying Köppen’s System

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Alluvial Fans & Mudflows Although deserts are dry—they do receive some precipitation, it just happens to be all at once, this is why flash floods are very common in desert regions. Because of this infrequent and intermittent rainfall, the desert is home to many unique and huge features. The drawing to the right depicts alluvial fans and a fan with an active mudflow. Alluvial fans can also be either identified as individual or collective features. When more than one alluvial fan touches, (coalesces) we call the new feature a Bajada. Please label the alluvial fan, bajada and mudflow on the diagram to the right. Other Features Found in Arid Environments Please match each vocabulary word with the best definition.

A flat-topped hill of resistant rock with very steep sides. Wider than it is High A thin, surface layer of closely packed pebbles. Rocks with flat, abraded surfaces caused by wind-blown sand. A bizarre-shaped column or pillar caused by differential erosion on rocks of different hardness. A dry desert gully, usually a small, narrow canyon with steep walls and flat, gravel strewn floor An isolated hill or mountain- paleo landform. A large, broad uplift with a flat top, several square miles to several 1,000 square miles in area. The flat, mud cracked bottom of the playa lake after it has dried up. A reddish-brown to white layer found in many desert soils: made mostly of calcium carbonate A flat-topped hill bounded by cliffs and capped with a resistant rock layer. Higher than it is Wide

Caliche Arroyo Plateau Inselberg Mesa Desert Pavement Hoodoo Playa Desert Ventifact Butte

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Dunes A dune is a hill of sand built by either wind or water flow. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind. The valley or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes. Large dune fields are known as ergs. The most common way that sediment is transported is by saltation. Please define the three possible ways that sediment is transported (use the diagram below for reference). 6. Saltation:

7. Suspension:

8. Creep: Please label and identify each dune: A: B: C: D: E: F:

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Feature Identification Please label and define clearly all eight features marked by the grey boxes in the provided diagram below. All of these features are either found within the lab or textbook, but do not hesitate to use your smart device for verification.