6.3 Internal waves and tsunamis

Internal waves and tsunamis are powerful forces shaping our oceans. These hidden phenomena occur beneath the surface, influencing everything from nutrient distribution to coastal safety. Understanding their formation and impacts is crucial for oceanographers and coastal communities alike.

Internal waves mix deep ocean waters, while tsunamis pose significant risks to coastal areas. Both types of waves transfer energy and momentum, affecting marine ecosystems and human activities. Detecting and predicting these waves is an ongoing challenge for scientists and disaster preparedness experts.

Internal Waves

Formation of internal ocean waves

Top images from around the web for Formation of internal ocean waves

• 

  18.1 The Topography of the Sea Floor – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  9.6 El Niño and La Niña – Introduction to Oceanography View original

  Is this image relevant?

• 

  9.8 Thermohaline Circulation – Introduction to Oceanography View original

  Is this image relevant?

• 

  18.1 The Topography of the Sea Floor – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  9.6 El Niño and La Niña – Introduction to Oceanography View original

  Is this image relevant?

1 of 3

Top images from around the web for Formation of internal ocean waves

• 

  18.1 The Topography of the Sea Floor – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  9.6 El Niño and La Niña – Introduction to Oceanography View original

  Is this image relevant?

• 

  9.8 Thermohaline Circulation – Introduction to Oceanography View original

  Is this image relevant?

• 

  18.1 The Topography of the Sea Floor – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  9.6 El Niño and La Niña – Introduction to Oceanography View original

  Is this image relevant?

1 of 3

• Disturbances at density interfaces within the ocean generate internal waves
• Interaction of tides with underwater topography (seamounts, continental shelves) creates oscillations
• Wind-driven surface disturbances propagate energy downward, initiating internal waves
• Seasonal changes in thermocline depth contribute to wave formation

Density stratification in wave generation

• Layers of water with different densities form due to variations in temperature and salinity
• Stronger stratification leads to more pronounced internal waves (thermocline, halocline)
• Buoyancy acts as primary restoring force, causing oscillations around equilibrium depth
• Pycnocline strength influences wave amplitude and frequency

Characteristics of internal waves

• Occur along density boundaries (pycnoclines) in ocean interior
• Travel horizontally and vertically, often at angles to the surface
• Move slower than surface waves (typical speeds 2-3 m/s)
• Wavelengths range from meters to kilometers
• Periods vary from minutes to hours, sometimes matching tidal cycles

Energy and momentum transfer

• Transport energy and momentum through ocean interior
• Contribute to mixing in deep ocean, affecting nutrient distribution
• Influence ocean circulation patterns and heat transport
• Interact with marine ecosystems, impacting plankton distribution

Observation and measurement techniques

• Satellite altimetry detects surface manifestations
• Acoustic Doppler Current Profilers (ADCPs) measure water column velocities
• Thermistor chains record temperature fluctuations at various depths
• Seismic oceanography uses low-frequency sound waves to image internal wave structures

Tsunamis

Tsunami causes and mechanisms

• Sudden displacement of large water volumes triggers series of waves
• Earthquakes with vertical seafloor displacement commonly cause tsunamis (subduction zones)
• Landslides (submarine or coastal) displace water, often earthquake-triggered
• Volcanic events (eruptions, flank collapses) generate waves through water displacement
• Rare events like meteorite impacts can also initiate tsunamis

Characteristics of tsunamis

• Extremely long wavelengths exceeding 100 km allow shallow water wave behavior
• Speed depends on ocean depth, calculated by $c = \sqrt{gh}$ (g = gravity, h = water depth)
• Deep ocean speeds reach over 800 km/h, slowing in shallow water
• Wave shoaling amplifies height as tsunami approaches shore
• Energy conservation enables transoceanic propagation with minimal loss

Coastal impacts and hazards

• Widespread inundation possible, extending kilometers inland in flat areas
• Destructive power from water mass and entrained debris
• Multiple waves arrive over hours, with first not always largest
• Rapid water level changes create strong currents, damaging structures
• Secondary hazards include contamination, fires, and infrastructure damage

Tsunami detection and mitigation

• Deep-ocean tsunami detection (DART) buoys measure pressure changes
• Seismic monitoring networks provide initial earthquake data
• Tide gauges and coastal stations monitor local sea level variations
• Warning centers analyze data, run models, issue alerts through various channels
• Hazard mapping and zoning regulations guide coastal development
• Public education and evacuation planning crucial for community preparedness

Challenges in tsunami preparedness

• Limited time for evacuation in near-field events (minutes to hours)
• Balancing false alarms with public safety in warning issuance
• Educating coastal populations about proper response actions
• Developing resilient infrastructure in tsunami-prone areas
• International cooperation needed for effective warning systems