Outline for class: Thursday, 25 February
Topic: Surf's Up
Annoucement:
Exam I: Thursday, 4 March, including material through Tuesday,
2 March. Bring to class an 882 scantron form and a #2 pencil.
Study questions and terms in the course reader (through waves)
and the TopClass exercise questions and quizzes.
In Class Activities:
- Beach sand is made of: quartz, feldspar and other minerals,
many different types of rock pieces (for example, basaltic lava
rock, granite, chert), and shells of organisms (usually calcium
carbonate minerals)
- Beach sand arrives at the beach primarily from: rivers, cliffs,
offshore (inner part of continental shelf), and longshore currents
- Beach parts: (1) backshore: with berms, sand dunes, cliffs,
sea walls, (2) foreshore: the intertidal zone, including the
beach face, (3) offshore: breakers and beyond.
- Berms: the winter berm tends to be further landward because
large storm waves remove sand from the beach; the summer berm
tends to be further seaward because small waves pile sand back
onto the beach. When sand is removed from the beach during winter,
that sand is carried offshore where it forms longshore bars (ridges
of sand the are underwater and parallel to the beach).
- Beach face: coarse-grained sand and gravel tend to produce
a steeply-sloping beach face, whereas fine-grained sand tends
to produce a gently-sloping beach face.
- Currents: (1) rip currents carry water (and sand) offshore
after breaking waves place water onto the beach; (2) longshore
currents carry water and sand parallel to the beach and result
from waves approaching the beach at an angle.
- Parts of a wave: crest, trough, wavelength (length between
successive crests); period is the time between successive crests;
ocean waves transmit energy through an orbital motion.
- Waves in shallow water: the wave's orbital motion extends
to a depth of about one-half the wavelength; when waves enter
shallow water (D< L/2), they begin to slow down, the wavelength
decreases, the height increases, and the wave breaks.
- Exercise 4: how are waves changed when they enter shallow
water.