⚙️ How-To Tsunamis Natural hazards & risk Notebook By

How to Count Tsunamis by Cause: Earthquakes, Landslides and Volcanoes

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Problem statement

Most tsunamis are raised by earthquakes under the sea, but the tallest waves in the record come from elsewhere: a rockslide into an Alaskan fjord, a volcano collapsing into the sea, a meteorological pressure jump that sends a wave along a coast. NOAA's database codes each event's cause, so tsunamis can be counted by cause and their heights and death tolls compared. The comparison holds a trap of its own: the maximum water height of a landslide tsunami is often measured on the slope of a narrow bay, a few hundred metres from where the rock fell, and is not comparable with an ocean-wide wave. This page counts causes and compares their heights, reach and deaths.

Quick answer

Name the cause codes and count events of validity 3 or 4:

CAUSE = {0: "unknown", 1: "earthquake", 2: "questionable earthquake", 3: "earthquake and landslide", 4: "volcano and earthquake",
         5: "volcano, earthquake and landslide", 6: "volcano", 7: "volcano and landslide", 8: "landslide", 9: "meteorological",
         10: "explosion", 11: "astronomical tide"}
sure = ev[ev.eventValidity >= 3].assign(cause=lambda d: d.causeCode.map(CAUSE))
print(sure.cause.value_counts().to_string())
cause
earthquake                           1219
landslide                             131
earthquake and landslide              115
meteorological                         76
volcano                                74
unknown                                48
volcano and landslide                  19
volcano and earthquake                  8
questionable earthquake                 5
volcano, earthquake and landslide       2
explosion                               2

Of 1,699 probable or definite tsunamis, 1,219 were raised by earthquakes, 72%. Landslides alone caused 131 and landslides set off by earthquakes another 115. 76 were meteorological, 74 volcanic and 19 caused by volcanic landslides. Two were explosions. The codes 2, 4 and 5 cover a few uncertain and mixed cases.

Horizontal bars on a log scale of probable and definite tsunamis by cause: 1,219 earthquake, 131 landslide, 115 earthquake and landslide, 76 meteorological, 74 volcano. Horizontal bars on a log scale of probable and definite tsunamis by cause: 1,219 earthquake, 131 landslide, 115 earthquake and landslide, 76 meteorological, 74 volcano.
What raised the tsunamis.

Height, reach and deaths

1. Maximum water height

print(sure.groupby("cause").maxWaterHeight.agg(["count", "median", "max"]).dropna().sort_values("count", ascending=False).round(1).head(7).to_string())
                          count  median    max
cause                                         
earthquake                  857     0.6   88.0
landslide                   102     7.0  481.0
earthquake and landslide     75     3.0  524.6
meteorological               66     0.7    7.0
volcano                      44     1.0   90.0
unknown                      29     2.2   30.0
volcano and landslide        17    10.0  250.0

The median earthquake tsunami reached 0.6 m at its highest point, and the median landslide tsunami 7.0 m, more than ten times as high. The maxima are further apart still: 88 m for an earthquake tsunami, 481 and 524.6 m for landslides. A landslide wave is tall near where it starts and dies away quickly.

2. How far they reach

far = ru[ru.runupHt > 0].groupby("tsunamiEventId").distFromSource.max().rename("reach_km")
r = sure.merge(far, left_on="id", right_index=True)
print(r.groupby("cause").reach_km.median().sort_values(ascending=False).round(0).head(6).to_string())
cause
earthquake                  359.0
earthquake and landslide    273.0
volcano and earthquake      101.0
meteorological               96.0
unknown                      83.0
volcano and landslide        80.0

Earthquake tsunamis reach furthest, a median of 359 km to the furthest run-up with a height, and earthquakes with landslides 273 km. Volcanic landslides, meteotsunamis and unknown causes reach about 80 to 100 km. The earthquake waves are the ones that cross oceans, because a fault rupture lifts the sea over hundreds of kilometres.

Box plots of maximum water height by cause on a log axis: earthquake tsunamis lowest, landslide and volcanic-landslide tsunamis highest. Box plots of maximum water height by cause on a log axis: earthquake tsunamis lowest, landslide and volcanic-landslide tsunamis highest.
Maximum water height by cause.

3. The tallest waves

print(sure.nlargest(6, "maxWaterHeight")[["year", "locationName", "cause", "maxWaterHeight", "numRunups"]].to_string(index=False))
 year             locationName                    cause  maxWaterHeight  numRunups
 1958           SE. ALASKA, AK earthquake and landslide           524.6         17
 2025            TRACY ARM, AK                landslide           481.0        178
 1980               WASHINGTON    volcano and landslide           250.0          2
 1963 VAJONT DAM, VAJONT RIVER                landslide           235.0          6
 2023 DICKSON FJORD, GREENLAND                landslide           200.0          5
 2015           TAAN FJORD, AK                landslide           193.0        316

The six tallest waves in the record are all landslides into narrow water: Lituya Bay in Alaska in 1958 at 524.6 m, Tracy Arm in Alaska in 2025 at 481 m, the 1980 eruption of Mount St Helens, which dropped its north flank into Spirit Lake, the Vajont reservoir in Italy in 1963, Dickson Fjord in Greenland in 2023 and Taan Fjord in Alaska in 2015. These heights are the water's reach up a slope opposite the slide. Rank them separately from ocean tsunamis, or leave them out of a ranking of wave heights.

Causes over time

The data used on this page

NOAA's Global Historical Tsunami Database from the National Centers for Environmental Information (doi:10.7289/V5PN93H7), public domain: every event and run-up from its HazEL API, downloaded on 19 October 2026 and saved on this site, because records are added and revised. Heights are in metres and distances in kilometres.

from pathlib import Path
import json
import zipfile

import geopandas as gpd
import numpy as np
import pandas as pd
import requests

Path("data").mkdir(exist_ok=True)
# NOAA NCEI Global Historical Tsunami Database (doi:10.7289/V5PN93H7): every event and every run-up from the HazEL API,
# with Natural Earth's 1:50m land and 1:110m countries. Saved 19 October 2026: events and run-ups are added and revised.
# Live: https://www.ngdc.noaa.gov/hazel/hazard-service/api/v1/tsunamis/events?page=1 (and .../runups), 200 a page
ARCHIVE = "ncei-tsunami-2026-10-19.zip"
if not Path(f"data/{ARCHIVE}").exists():
    Path(f"data/{ARCHIVE}").write_bytes(requests.get(f"https://data.spatialworkflow.io/{ARCHIVE}", timeout=600).content)
Z = zipfile.ZipFile(f"data/{ARCHIVE}")
ev = pd.DataFrame(json.loads(Z.read("tsunami-events.json")))
ru = pd.DataFrame(json.loads(Z.read("tsunami-runups.json")))
print(f"NCEI tsunami database: {len(ev):,} events, {len(ru):,} run-ups")
NCEI tsunami database: 3,138 events, 35,129 run-ups

Example 1: share of each cause since 1900

s = sure[sure.year >= 1900]
print(s.cause.value_counts(normalize=True).head(6).round(3).to_string())
cause
earthquake                  0.710
landslide                   0.096
meteorological              0.064
earthquake and landslide    0.057
volcano                     0.041
volcano and landslide       0.012

Since 1900, earthquakes caused 71.0% of probable and definite tsunamis, landslides 9.6% and meteorological events 6.4%. The meteotsunami share has grown as tide gauges began recording the small, weather-driven waves that rarely made the news before.

Horizontal bars of the ten tallest tsunamis, all involving landslides: Lituya Bay 1958 at 524.6 m, Tracy Arm 2025 at 481 m, Mount St Helens 1980 at 250 m. Horizontal bars of the ten tallest tsunamis, all involving landslides: Lituya Bay 1958 at 524.6 m, Tracy Arm 2025 at 481 m, Mount St Helens 1980 at 250 m.
The tallest tsunamis.

Example 2: earthquake depth

q = sure[(sure.causeCode == 1) & sure.eqDepth.notna()]
print(q.groupby(pd.cut(q.eqDepth, [0, 20, 40, 70, 300, 700])).maxWaterHeight.agg(["size", "median"]).round(2).to_string())
            size  median
eqDepth                 
(0, 20]      296    0.30
(20, 40]     365    0.50
(40, 70]     111    0.38
(70, 300]     32    0.17
(300, 700]     1     NaN

Among earthquake tsunamis, depth matters less than you might expect: the median maximum height is 0.3 m for earthquakes up to 20 km deep, 0.5 m for 20 to 40 km and 0.38 m for 40 to 70 km. Deeper earthquakes, below 70 km, raise smaller waves, a median of 0.17 m, because they move the sea floor less. Magnitude, on the validity page, makes far more difference.