6.3 Internal waves and tsunamis
3 min read•july 24, 2024
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 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 (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 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
Key Terms to Review (17)
Buoy data: Buoy data refers to the information collected by floating devices known as buoys, which are deployed in oceans and other bodies of water to monitor various environmental parameters. These buoys can provide valuable insights into ocean conditions, including temperature, wave heights, currents, and atmospheric pressure, playing a crucial role in understanding phenomena like internal waves and tsunamis.
Dispersion: Dispersion is the process by which waves or particles spread out from a central point, often influenced by various environmental factors. In the context of oceanography, dispersion refers to how internal waves and tsunamis propagate through water, affecting their speed and energy distribution. This spreading can significantly impact coastal areas and marine ecosystems, highlighting the importance of understanding these dynamics.
Ecosystem disruption: Ecosystem disruption refers to significant disturbances that alter the structure and function of an ecosystem, often leading to changes in species composition, habitat loss, and ecological balance. Such disruptions can be triggered by natural events or human activities, resulting in immediate and long-lasting effects on marine environments, including alterations in food webs and biodiversity.
Inundation: Inundation refers to the flooding or submergence of land due to the rising of water levels, often associated with natural disasters like tsunamis and internal waves. This phenomenon can lead to significant environmental changes, impacting ecosystems, human settlements, and coastal infrastructures. Understanding inundation is essential when studying the dynamics of oceanic waves and their potential effects on coastal areas.
Non-linear wave theory: Non-linear wave theory is a framework used to describe wave behavior in which the amplitude of the waves affects their speed and shape. This theory recognizes that in certain conditions, waves can interact in complex ways, leading to phenomena such as wave steepening, breaking, and the formation of solitons. These characteristics are especially relevant when studying internal waves and tsunamis, where the dynamics can deviate significantly from linear models.
Reflection: Reflection is the bouncing back of a wave when it encounters a boundary or obstacle. In the context of internal waves and tsunamis, reflection plays a critical role in how these waves interact with different layers of water and the ocean floor, affecting their behavior, energy distribution, and potential impacts on coastal areas.
Sediment resuspension: Sediment resuspension is the process by which sediments that have settled on the seafloor are disturbed and lifted back into the water column. This phenomenon can be caused by various factors, including waves, currents, and other hydrodynamic forces. When internal waves or tsunamis occur, they can generate powerful flows that stir up sediments, impacting water clarity and nutrient distribution in marine ecosystems.
Shoreline erosion: Shoreline erosion refers to the process in which coastal land is gradually worn away by the action of waves, currents, tides, and human activities. This natural phenomenon can reshape coastlines, leading to loss of land and changes in coastal ecosystems. Factors such as storm events, rising sea levels, and human interference can significantly accelerate erosion, posing risks to coastal communities and infrastructure.
Solitons: Solitons are stable, solitary wave packets that maintain their shape while traveling at constant speed, arising in nonlinear systems. These waves are significant in the study of various ocean phenomena, especially internal waves and tsunamis, as they can convey energy across long distances without dissipating.
Subduction Zone: A subduction zone is a geologic feature where one tectonic plate moves under another plate and sinks into the mantle, leading to significant geological activity. These zones are often associated with the formation of deep ocean trenches, volcanic arcs, and intense seismic activity, which play crucial roles in shaping ocean basins and the overall bathymetry of the seafloor. Subduction zones are also vital in understanding the generation of internal waves and tsunamis, as they are common locations for underwater earthquakes.
Thermohaline waves: Thermohaline waves are internal waves that occur in the ocean due to variations in temperature and salinity, which affect water density. These waves play a significant role in ocean dynamics, particularly in how they influence mixing and the movement of water masses at different depths. By interacting with various factors like tides and currents, thermohaline waves can create complex flow patterns and contribute to larger oceanic processes such as the thermohaline circulation.
Tremendous Wave Theory: Tremendous wave theory refers to the scientific understanding of the formation and behavior of extremely large ocean waves, such as tsunamis and rogue waves, emphasizing their significant energy and impact on coastal areas. This theory helps explain how these waves are generated, their propagation across the ocean, and the complex interactions with underwater topography that influence their height and energy when they reach shore.
Tsunami gauge: A tsunami gauge is a specialized instrument used to detect and measure the height and speed of tsunami waves in order to provide timely data for early warning systems. These gauges are critical for monitoring ocean conditions, particularly in areas prone to tsunamis, as they help forecast potential impacts and protect coastal communities. They play an essential role in enhancing our understanding of tsunami dynamics and the potential risks associated with these powerful waves.
Tsunami propagation: Tsunami propagation refers to the movement and travel of tsunami waves across the ocean after being generated by disturbances such as underwater earthquakes, volcanic eruptions, or landslides. These waves can travel across vast distances, sometimes reaching speeds of up to 500-800 km/h in deep water and are capable of impacting coastal areas far from their source. Understanding tsunami propagation is crucial for predicting wave behavior and assessing potential risks to coastal communities.
Underwater landslide: An underwater landslide is a sudden and rapid movement of sediment and rock down the continental slope or shelf into the ocean. These slides can be triggered by various factors, including earthquakes, volcanic activity, or heavy rainfall, and can lead to significant geological and oceanographic consequences, including the generation of tsunamis and internal waves.
Wave amplitude: Wave amplitude refers to the maximum distance that points on a wave, such as a water wave, move from their rest position. It is an important measure in understanding the energy and strength of a wave, as higher amplitudes typically indicate more energy. In the context of waves like internal waves and tsunamis, amplitude plays a crucial role in determining their potential impact on marine environments and coastal regions.
Wave run-up: Wave run-up is the maximum vertical distance that a wave ascends above the still water level when it reaches the shore. This phenomenon is crucial in understanding how waves interact with coastal environments, as it affects coastal erosion, sediment transport, and habitat dynamics.